* Re: [PATCH] cxl/hdm: fix a warning in devm_remove_action()
2026-03-09 0:08 [PATCH] cxl/hdm: fix a warning in devm_remove_action() Sungwoo Kim
@ 2026-03-09 19:31 ` Ira Weiny
2026-03-09 20:21 ` Dave Jiang
` (2 subsequent siblings)
3 siblings, 0 replies; 8+ messages in thread
From: Ira Weiny @ 2026-03-09 19:31 UTC (permalink / raw)
To: Sungwoo Kim, Davidlohr Bueso, Jonathan Cameron, Dave Jiang,
Alison Schofield, Vishal Verma, Ira Weiny, Dan Williams,
Ben Widawsky
Cc: Dave Tian, Sungwoo Kim, Jonathan Cameron, linux-cxl, linux-kernel
Sungwoo Kim wrote:
> In the following race scenario, devm_remove_action() can be called
> before devm_add_action(), triggering a warning because there is no
> action to remove.
>
> To fix this, extend a critical section to embrace both
> __cxl_dpa_reserve() and devm_add_action().
>
> task 1:
> cxl_dpa_alloc()
> __cxl_dpa_reserve() ...(1)
> devm_add_action() ...(4)
>
> task 2:
> cxl_dpa_free()
> guard()
> if (!cxled->dpa_res) ...(2) pass, due to (1)
> return 0;
> devm_cxl_dpa_release()
> devm_remove_action() ...(3) warning, no action is added yet
>
> Warning log:
>
[snip]
>
> Fixes: cf880423b6a0 ("cxl/hdm: Add support for allocating DPA to an endpoint decoder")
> Fixes: 9c57cde0dcbd ("cxl/hdm: Enumerate allocated DPA")
> Signed-off-by: Sungwoo Kim <iam@sung-woo.kim>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
[snip]
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH] cxl/hdm: fix a warning in devm_remove_action()
2026-03-09 0:08 [PATCH] cxl/hdm: fix a warning in devm_remove_action() Sungwoo Kim
2026-03-09 19:31 ` Ira Weiny
@ 2026-03-09 20:21 ` Dave Jiang
2026-03-24 4:06 ` Sungwoo Kim
2026-03-25 0:46 ` Alison Schofield
2026-03-25 1:34 ` Dan Williams
3 siblings, 1 reply; 8+ messages in thread
From: Dave Jiang @ 2026-03-09 20:21 UTC (permalink / raw)
To: Sungwoo Kim, Davidlohr Bueso, Jonathan Cameron, Alison Schofield,
Vishal Verma, Ira Weiny, Dan Williams, Ben Widawsky
Cc: Dave Tian, linux-cxl, linux-kernel
On 3/8/26 5:08 PM, Sungwoo Kim wrote:
> In the following race scenario, devm_remove_action() can be called
> before devm_add_action(), triggering a warning because there is no
> action to remove.
>
> To fix this, extend a critical section to embrace both
> __cxl_dpa_reserve() and devm_add_action().
>
> task 1:
> cxl_dpa_alloc()
> __cxl_dpa_reserve() ...(1)
> devm_add_action() ...(4)
>
> task 2:
> cxl_dpa_free()
> guard()
> if (!cxled->dpa_res) ...(2) pass, due to (1)
> return 0;
> devm_cxl_dpa_release()
> devm_remove_action() ...(3) warning, no action is added yet
>
> Warning log:
>
> WARNING: ./include/linux/device/devres.h:160 at devm_remove_action include/linux/device/devres.h:160 [inline], CPU#0: syz.1.6464/25993
> WARNING: ./include/linux/device/devres.h:160 at devm_cxl_dpa_release drivers/cxl/core/hdm.c:290 [inline], CPU#0: syz.1.6464/25993
> WARNING: ./include/linux/device/devres.h:160 at cxl_dpa_free+0x2a4/0x320 drivers/cxl/core/hdm.c:572, CPU#0: syz.1.6464/25993
> Modules linked in:
> CPU: 0 UID: 0 PID: 25993 Comm: syz.1.6464 Not tainted 6.19.0-g15a37b05f387 #10 PREEMPT(lazy)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014
> RIP: 0010:devm_remove_action include/linux/device/devres.h:160 [inline]
> RIP: 0010:devm_cxl_dpa_release drivers/cxl/core/hdm.c:290 [inline]
> RIP: 0010:cxl_dpa_free+0x2a4/0x320 drivers/cxl/core/hdm.c:572
> Code: 01 31 ff 41 89 c4 89 c6 e8 a9 91 1d fe 45 85 e4 0f 85 55 ff ff ff e8 4b 96 1d fe 90 0f 0b 90 e9 47 ff ff ff e8 3d 96 1d fe 90 <0f> 0b 90 e9 63 ff ff ff bb f0 ff ff ff e9 68 ff ff ff 48 c7 c7 f4
> RSP: 0018:ffff888129f77bb8 EFLAGS: 00010282
> RAX: 00000000000000f3 RBX: ffff888102f64000 RCX: ffffffff837301d3
> RDX: 0000000000080000 RSI: ffffc90001c5a000 RDI: 0000000000000005
> RBP: 00000000fffffffe R08: 0000000000000001 R09: ffff888123f98000
> R10: 00000000fffffffe R11: 0000000000000000 R12: 0000000000000001
> R13: ffff888102f64040 R14: dffffc0000000000 R15: ffff888102f64000
> FS: 00007fae0488d6c0(0000) GS:ffff88827086d000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000000 CR3: 000000012f7d6003 CR4: 0000000000770ef0
> PKRU: 80000000
> Call Trace:
> <TASK>
> dpa_size_store+0xfb/0x230 drivers/cxl/core/port.c:269
> dev_attr_store+0x58/0x80 drivers/base/core.c:2437
> sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
> kernfs_fop_write_iter+0x3d6/0x5d0 fs/kernfs/file.c:352
> new_sync_write fs/read_write.c:595 [inline]
> vfs_write+0x68e/0x1050 fs/read_write.c:688
> ksys_write+0x12a/0x250 fs/read_write.c:740
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xfc/0x670 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fae0399c669
> Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fae0488d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 00007fae03c15fa0 RCX: 00007fae0399c669
> RDX: 000000000000000a RSI: 00002000000001c0 RDI: 0000000000000009
> RBP: 00007fae03a32c71 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fae03c16038 R14: 00007fae03c15fa0 R15: 00007ffe53519fb8
> </TASK>
> irq event stamp: 1021
> hardirqs last enabled at (1029): [<ffffffffb7d04c4b>] __up_console_sem+0x7b/0x90 kernel/printk/printk.c:347
> hardirqs last disabled at (1038): [<ffffffffb7d04c30>] __up_console_sem+0x60/0x90 kernel/printk/printk.c:345
> softirqs last enabled at (1016): [<ffffffffb7b73b93>] __do_softirq kernel/softirq.c:656 [inline]
> softirqs last enabled at (1016): [<ffffffffb7b73b93>] invoke_softirq kernel/softirq.c:496 [inline]
> softirqs last enabled at (1016): [<ffffffffb7b73b93>] __irq_exit_rcu+0xb3/0xe0 kernel/softirq.c:723
> softirqs last disabled at (1005): [<ffffffffb7b73b93>] __do_softirq kernel/softirq.c:656 [inline]
> softirqs last disabled at (1005): [<ffffffffb7b73b93>] invoke_softirq kernel/softirq.c:496 [inline]
> softirqs last disabled at (1005): [<ffffffffb7b73b93>] __irq_exit_rcu+0xb3/0xe0 kernel/softirq.c:723
>
> Fixes: cf880423b6a0 ("cxl/hdm: Add support for allocating DPA to an endpoint decoder")
> Fixes: 9c57cde0dcbd ("cxl/hdm: Enumerate allocated DPA")
> Signed-off-by: Sungwoo Kim <iam@sung-woo.kim>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> ---
> drivers/cxl/core/hdm.c | 34 +++++++++++++++++++++++++++++-----
> 1 file changed, 29 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index e3f0c39e68124..86239b1790a31 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -509,13 +509,20 @@ int devm_cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
> struct cxl_port *port = cxled_to_port(cxled);
> int rc;
>
> - scoped_guard(rwsem_write, &cxl_rwsem.dpa)
> - rc = __cxl_dpa_reserve(cxled, base, len, skipped);
> + guard(rwsem_write)(&cxl_rwsem.dpa);
> + rc = __cxl_dpa_reserve(cxled, base, len, skipped);
>
> if (rc)
> return rc;
>
> - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
> + /* See comments in cxl_dpa_alloc()*/
> + rc = devm_add_action(&port->dev, cxl_dpa_release, cxled);
> + if (rc) {
> + __cxl_dpa_release(cxled);
> + return rc;
> + }
> +
> + return 0;
> }
> EXPORT_SYMBOL_NS_GPL(devm_cxl_dpa_reserve, "CXL");
>
> @@ -613,7 +620,7 @@ static int __cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size)
> struct resource *p, *last;
> int part;
>
> - guard(rwsem_write)(&cxl_rwsem.dpa);
> + lockdep_assert_held_write(&cxl_rwsem.dpa);
> if (cxled->cxld.region) {
> dev_dbg(dev, "decoder attached to %s\n",
> dev_name(&cxled->cxld.region->dev));
> @@ -679,11 +686,28 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size)
> struct cxl_port *port = cxled_to_port(cxled);
> int rc;
>
> + guard(rwsem_write)(&cxl_rwsem.dpa);
> rc = __cxl_dpa_alloc(cxled, size);
> if (rc)
> return rc;
>
> - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
> + /*
> + * Add the devres action while still holding cxl_rwsem.dpa to prevent
> + * a race with cxl_dpa_free(). Without this, a concurrent cxl_dpa_free()
> + * can observe dpa_res set (by __cxl_dpa_reserve()) and attempt
> + * devm_remove_action() before devm_add_action() has been called,
> + * triggering a WARN_ON in devm_remove_action().
> + * Also, devm_add_action_or_reset() cannot be used here because
> + * cxl_dpa_release() tries to hold the dpa lock that is already held,
> + * causing a self deadlock.
> + */
> + rc = devm_add_action(&port->dev, cxl_dpa_release, cxled);
> + if (rc) {
> + __cxl_dpa_release(cxled);
> + return rc;
> + }
> +
> + return 0;
> }
>
> static void cxld_set_interleave(struct cxl_decoder *cxld, u32 *ctrl)
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH] cxl/hdm: fix a warning in devm_remove_action()
2026-03-09 20:21 ` Dave Jiang
@ 2026-03-24 4:06 ` Sungwoo Kim
0 siblings, 0 replies; 8+ messages in thread
From: Sungwoo Kim @ 2026-03-24 4:06 UTC (permalink / raw)
To: Dave Jiang
Cc: Davidlohr Bueso, Jonathan Cameron, Alison Schofield,
Vishal Verma, Ira Weiny, Dan Williams, Ben Widawsky, Dave Tian,
linux-cxl, linux-kernel
Hello,
I'd like to gently follow up on this patch.
Are there any concerns or issues about the patch that I should address
before it can be merged?
Best,
Sungwoo.
On Mon, Mar 9, 2026 at 4:21 PM Dave Jiang <dave.jiang@intel.com> wrote:
>
>
>
> On 3/8/26 5:08 PM, Sungwoo Kim wrote:
> > In the following race scenario, devm_remove_action() can be called
> > before devm_add_action(), triggering a warning because there is no
> > action to remove.
> >
> > To fix this, extend a critical section to embrace both
> > __cxl_dpa_reserve() and devm_add_action().
> >
> > task 1:
> > cxl_dpa_alloc()
> > __cxl_dpa_reserve() ...(1)
> > devm_add_action() ...(4)
> >
> > task 2:
> > cxl_dpa_free()
> > guard()
> > if (!cxled->dpa_res) ...(2) pass, due to (1)
> > return 0;
> > devm_cxl_dpa_release()
> > devm_remove_action() ...(3) warning, no action is added yet
> >
> > Warning log:
> >
> > WARNING: ./include/linux/device/devres.h:160 at devm_remove_action include/linux/device/devres.h:160 [inline], CPU#0: syz.1.6464/25993
> > WARNING: ./include/linux/device/devres.h:160 at devm_cxl_dpa_release drivers/cxl/core/hdm.c:290 [inline], CPU#0: syz.1.6464/25993
> > WARNING: ./include/linux/device/devres.h:160 at cxl_dpa_free+0x2a4/0x320 drivers/cxl/core/hdm.c:572, CPU#0: syz.1.6464/25993
> > Modules linked in:
> > CPU: 0 UID: 0 PID: 25993 Comm: syz.1.6464 Not tainted 6.19.0-g15a37b05f387 #10 PREEMPT(lazy)
> > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014
> > RIP: 0010:devm_remove_action include/linux/device/devres.h:160 [inline]
> > RIP: 0010:devm_cxl_dpa_release drivers/cxl/core/hdm.c:290 [inline]
> > RIP: 0010:cxl_dpa_free+0x2a4/0x320 drivers/cxl/core/hdm.c:572
> > Code: 01 31 ff 41 89 c4 89 c6 e8 a9 91 1d fe 45 85 e4 0f 85 55 ff ff ff e8 4b 96 1d fe 90 0f 0b 90 e9 47 ff ff ff e8 3d 96 1d fe 90 <0f> 0b 90 e9 63 ff ff ff bb f0 ff ff ff e9 68 ff ff ff 48 c7 c7 f4
> > RSP: 0018:ffff888129f77bb8 EFLAGS: 00010282
> > RAX: 00000000000000f3 RBX: ffff888102f64000 RCX: ffffffff837301d3
> > RDX: 0000000000080000 RSI: ffffc90001c5a000 RDI: 0000000000000005
> > RBP: 00000000fffffffe R08: 0000000000000001 R09: ffff888123f98000
> > R10: 00000000fffffffe R11: 0000000000000000 R12: 0000000000000001
> > R13: ffff888102f64040 R14: dffffc0000000000 R15: ffff888102f64000
> > FS: 00007fae0488d6c0(0000) GS:ffff88827086d000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000000000000000 CR3: 000000012f7d6003 CR4: 0000000000770ef0
> > PKRU: 80000000
> > Call Trace:
> > <TASK>
> > dpa_size_store+0xfb/0x230 drivers/cxl/core/port.c:269
> > dev_attr_store+0x58/0x80 drivers/base/core.c:2437
> > sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
> > kernfs_fop_write_iter+0x3d6/0x5d0 fs/kernfs/file.c:352
> > new_sync_write fs/read_write.c:595 [inline]
> > vfs_write+0x68e/0x1050 fs/read_write.c:688
> > ksys_write+0x12a/0x250 fs/read_write.c:740
> > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> > do_syscall_64+0xfc/0x670 arch/x86/entry/syscall_64.c:94
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > RIP: 0033:0x7fae0399c669
> > Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007fae0488d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> > RAX: ffffffffffffffda RBX: 00007fae03c15fa0 RCX: 00007fae0399c669
> > RDX: 000000000000000a RSI: 00002000000001c0 RDI: 0000000000000009
> > RBP: 00007fae03a32c71 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> > R13: 00007fae03c16038 R14: 00007fae03c15fa0 R15: 00007ffe53519fb8
> > </TASK>
> > irq event stamp: 1021
> > hardirqs last enabled at (1029): [<ffffffffb7d04c4b>] __up_console_sem+0x7b/0x90 kernel/printk/printk.c:347
> > hardirqs last disabled at (1038): [<ffffffffb7d04c30>] __up_console_sem+0x60/0x90 kernel/printk/printk.c:345
> > softirqs last enabled at (1016): [<ffffffffb7b73b93>] __do_softirq kernel/softirq.c:656 [inline]
> > softirqs last enabled at (1016): [<ffffffffb7b73b93>] invoke_softirq kernel/softirq.c:496 [inline]
> > softirqs last enabled at (1016): [<ffffffffb7b73b93>] __irq_exit_rcu+0xb3/0xe0 kernel/softirq.c:723
> > softirqs last disabled at (1005): [<ffffffffb7b73b93>] __do_softirq kernel/softirq.c:656 [inline]
> > softirqs last disabled at (1005): [<ffffffffb7b73b93>] invoke_softirq kernel/softirq.c:496 [inline]
> > softirqs last disabled at (1005): [<ffffffffb7b73b93>] __irq_exit_rcu+0xb3/0xe0 kernel/softirq.c:723
> >
> > Fixes: cf880423b6a0 ("cxl/hdm: Add support for allocating DPA to an endpoint decoder")
> > Fixes: 9c57cde0dcbd ("cxl/hdm: Enumerate allocated DPA")
> > Signed-off-by: Sungwoo Kim <iam@sung-woo.kim>
>
> Reviewed-by: Dave Jiang <dave.jiang@intel.com>
>
>
> > ---
> > drivers/cxl/core/hdm.c | 34 +++++++++++++++++++++++++++++-----
> > 1 file changed, 29 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> > index e3f0c39e68124..86239b1790a31 100644
> > --- a/drivers/cxl/core/hdm.c
> > +++ b/drivers/cxl/core/hdm.c
> > @@ -509,13 +509,20 @@ int devm_cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
> > struct cxl_port *port = cxled_to_port(cxled);
> > int rc;
> >
> > - scoped_guard(rwsem_write, &cxl_rwsem.dpa)
> > - rc = __cxl_dpa_reserve(cxled, base, len, skipped);
> > + guard(rwsem_write)(&cxl_rwsem.dpa);
> > + rc = __cxl_dpa_reserve(cxled, base, len, skipped);
> >
> > if (rc)
> > return rc;
> >
> > - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
> > + /* See comments in cxl_dpa_alloc()*/
> > + rc = devm_add_action(&port->dev, cxl_dpa_release, cxled);
> > + if (rc) {
> > + __cxl_dpa_release(cxled);
> > + return rc;
> > + }
> > +
> > + return 0;
> > }
> > EXPORT_SYMBOL_NS_GPL(devm_cxl_dpa_reserve, "CXL");
> >
> > @@ -613,7 +620,7 @@ static int __cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size)
> > struct resource *p, *last;
> > int part;
> >
> > - guard(rwsem_write)(&cxl_rwsem.dpa);
> > + lockdep_assert_held_write(&cxl_rwsem.dpa);
> > if (cxled->cxld.region) {
> > dev_dbg(dev, "decoder attached to %s\n",
> > dev_name(&cxled->cxld.region->dev));
> > @@ -679,11 +686,28 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size)
> > struct cxl_port *port = cxled_to_port(cxled);
> > int rc;
> >
> > + guard(rwsem_write)(&cxl_rwsem.dpa);
> > rc = __cxl_dpa_alloc(cxled, size);
> > if (rc)
> > return rc;
> >
> > - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
> > + /*
> > + * Add the devres action while still holding cxl_rwsem.dpa to prevent
> > + * a race with cxl_dpa_free(). Without this, a concurrent cxl_dpa_free()
> > + * can observe dpa_res set (by __cxl_dpa_reserve()) and attempt
> > + * devm_remove_action() before devm_add_action() has been called,
> > + * triggering a WARN_ON in devm_remove_action().
> > + * Also, devm_add_action_or_reset() cannot be used here because
> > + * cxl_dpa_release() tries to hold the dpa lock that is already held,
> > + * causing a self deadlock.
> > + */
> > + rc = devm_add_action(&port->dev, cxl_dpa_release, cxled);
> > + if (rc) {
> > + __cxl_dpa_release(cxled);
> > + return rc;
> > + }
> > +
> > + return 0;
> > }
> >
> > static void cxld_set_interleave(struct cxl_decoder *cxld, u32 *ctrl)
>
>
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] cxl/hdm: fix a warning in devm_remove_action()
2026-03-09 0:08 [PATCH] cxl/hdm: fix a warning in devm_remove_action() Sungwoo Kim
2026-03-09 19:31 ` Ira Weiny
2026-03-09 20:21 ` Dave Jiang
@ 2026-03-25 0:46 ` Alison Schofield
2026-03-25 22:34 ` Sungwoo Kim
2026-03-25 1:34 ` Dan Williams
3 siblings, 1 reply; 8+ messages in thread
From: Alison Schofield @ 2026-03-25 0:46 UTC (permalink / raw)
To: Sungwoo Kim
Cc: Davidlohr Bueso, Jonathan Cameron, Dave Jiang, Vishal Verma,
Ira Weiny, Dan Williams, Ben Widawsky, Dave Tian, linux-cxl,
linux-kernel
On Sun, Mar 08, 2026 at 08:08:10PM -0400, Sungwoo Kim wrote:
> In the following race scenario, devm_remove_action() can be called
> before devm_add_action(), triggering a warning because there is no
> action to remove.
>
> To fix this, extend a critical section to embrace both
> __cxl_dpa_reserve() and devm_add_action().
The fix LGTM. I suggest tightening up the code comment. Now it
talks through the race in detail and also cross-ref another location.
Limit the comment to describing the ordering requirement we need to
preserve. The commit message already captures the full race and
rationale.
Comment update suggestion below-
snip
> +++ b/drivers/cxl/core/hdm.c
> @@ -509,13 +509,20 @@ int devm_cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
> struct cxl_port *port = cxled_to_port(cxled);
> int rc;
>
> - scoped_guard(rwsem_write, &cxl_rwsem.dpa)
> - rc = __cxl_dpa_reserve(cxled, base, len, skipped);
> + guard(rwsem_write)(&cxl_rwsem.dpa);
> + rc = __cxl_dpa_reserve(cxled, base, len, skipped);
>
> if (rc)
> return rc;
>
> - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
> + /* See comments in cxl_dpa_alloc()*/
Something like this:
/* Keep reservation and devres registration ordered under dpa lock */
snip
> @@ -613,7 +620,7 @@ static int __cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size)
> struct resource *p, *last;
> int part;
>
> - guard(rwsem_write)(&cxl_rwsem.dpa);
> + lockdep_assert_held_write(&cxl_rwsem.dpa);
> if (cxled->cxld.region) {
> dev_dbg(dev, "decoder attached to %s\n",
> dev_name(&cxled->cxld.region->dev));
> @@ -679,11 +686,28 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size)
> struct cxl_port *port = cxled_to_port(cxled);
> int rc;
>
> + guard(rwsem_write)(&cxl_rwsem.dpa);
> rc = __cxl_dpa_alloc(cxled, size);
> if (rc)
> return rc;
>
> - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
> + /*
> + * Add the devres action while still holding cxl_rwsem.dpa to prevent
> + * a race with cxl_dpa_free(). Without this, a concurrent cxl_dpa_free()
> + * can observe dpa_res set (by __cxl_dpa_reserve()) and attempt
> + * devm_remove_action() before devm_add_action() has been called,
> + * triggering a WARN_ON in devm_remove_action().
> + * Also, devm_add_action_or_reset() cannot be used here because
> + * cxl_dpa_release() tries to hold the dpa lock that is already held,
> + * causing a self deadlock.
> + */
and like this:
/*
* Hold cxl_rwsem.dpa across allocation and devres registration
* so cxl_dpa_free() cannot observe dpa_res without a matching
* devres action.
*/
snip
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH] cxl/hdm: fix a warning in devm_remove_action()
2026-03-25 0:46 ` Alison Schofield
@ 2026-03-25 22:34 ` Sungwoo Kim
0 siblings, 0 replies; 8+ messages in thread
From: Sungwoo Kim @ 2026-03-25 22:34 UTC (permalink / raw)
To: Alison Schofield
Cc: Davidlohr Bueso, Jonathan Cameron, Dave Jiang, Vishal Verma,
Ira Weiny, Dan Williams, Ben Widawsky, Dave Tian, linux-cxl,
linux-kernel
On Tue, Mar 24, 2026 at 8:46 PM Alison Schofield
<alison.schofield@intel.com> wrote:
>
> On Sun, Mar 08, 2026 at 08:08:10PM -0400, Sungwoo Kim wrote:
> > In the following race scenario, devm_remove_action() can be called
> > before devm_add_action(), triggering a warning because there is no
> > action to remove.
> >
> > To fix this, extend a critical section to embrace both
> > __cxl_dpa_reserve() and devm_add_action().
>
> The fix LGTM. I suggest tightening up the code comment. Now it
> talks through the race in detail and also cross-ref another location.
> Limit the comment to describing the ordering requirement we need to
> preserve. The commit message already captures the full race and
> rationale.
>
> Comment update suggestion below-
>
> snip
>
> > +++ b/drivers/cxl/core/hdm.c
> > @@ -509,13 +509,20 @@ int devm_cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
> > struct cxl_port *port = cxled_to_port(cxled);
> > int rc;
> >
> > - scoped_guard(rwsem_write, &cxl_rwsem.dpa)
> > - rc = __cxl_dpa_reserve(cxled, base, len, skipped);
> > + guard(rwsem_write)(&cxl_rwsem.dpa);
> > + rc = __cxl_dpa_reserve(cxled, base, len, skipped);
> >
> > if (rc)
> > return rc;
> >
> > - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
> > + /* See comments in cxl_dpa_alloc()*/
>
> Something like this:
> /* Keep reservation and devres registration ordered under dpa lock */
>
>
> snip
>
> > @@ -613,7 +620,7 @@ static int __cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size)
> > struct resource *p, *last;
> > int part;
> >
> > - guard(rwsem_write)(&cxl_rwsem.dpa);
> > + lockdep_assert_held_write(&cxl_rwsem.dpa);
> > if (cxled->cxld.region) {
> > dev_dbg(dev, "decoder attached to %s\n",
> > dev_name(&cxled->cxld.region->dev));
> > @@ -679,11 +686,28 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size)
> > struct cxl_port *port = cxled_to_port(cxled);
> > int rc;
> >
> > + guard(rwsem_write)(&cxl_rwsem.dpa);
> > rc = __cxl_dpa_alloc(cxled, size);
> > if (rc)
> > return rc;
> >
> > - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
> > + /*
> > + * Add the devres action while still holding cxl_rwsem.dpa to prevent
> > + * a race with cxl_dpa_free(). Without this, a concurrent cxl_dpa_free()
> > + * can observe dpa_res set (by __cxl_dpa_reserve()) and attempt
> > + * devm_remove_action() before devm_add_action() has been called,
> > + * triggering a WARN_ON in devm_remove_action().
> > + * Also, devm_add_action_or_reset() cannot be used here because
> > + * cxl_dpa_release() tries to hold the dpa lock that is already held,
> > + * causing a self deadlock.
> > + */
>
> and like this:
>
> /*
> * Hold cxl_rwsem.dpa across allocation and devres registration
> * so cxl_dpa_free() cannot observe dpa_res without a matching
> * devres action.
> */
>
> snip
>
Thank you for your review with a suggestion. Will do in V2.
Resending to the mailing list, I replied privately by mistake.
Sungwoo.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] cxl/hdm: fix a warning in devm_remove_action()
2026-03-09 0:08 [PATCH] cxl/hdm: fix a warning in devm_remove_action() Sungwoo Kim
` (2 preceding siblings ...)
2026-03-25 0:46 ` Alison Schofield
@ 2026-03-25 1:34 ` Dan Williams
2026-03-25 3:47 ` Sungwoo Kim
3 siblings, 1 reply; 8+ messages in thread
From: Dan Williams @ 2026-03-25 1:34 UTC (permalink / raw)
To: Sungwoo Kim, Davidlohr Bueso, Jonathan Cameron, Dave Jiang,
Alison Schofield, Vishal Verma, Ira Weiny, Dan Williams,
Ben Widawsky
Cc: Dave Tian, Sungwoo Kim, Jonathan Cameron, linux-cxl, linux-kernel
Sungwoo Kim wrote:
> In the following race scenario, devm_remove_action() can be called
> before devm_add_action(), triggering a warning because there is no
> action to remove.
>
> To fix this, extend a critical section to embrace both
> __cxl_dpa_reserve() and devm_add_action().
>
> task 1:
> cxl_dpa_alloc()
> __cxl_dpa_reserve() ...(1)
> devm_add_action() ...(4)
>
> task 2:
> cxl_dpa_free()
> guard()
> if (!cxled->dpa_res) ...(2) pass, due to (1)
> return 0;
> devm_cxl_dpa_release()
> devm_remove_action() ...(3) warning, no action is added yet
>
> Warning log:
>
> WARNING: ./include/linux/device/devres.h:160 at devm_remove_action include/linux/device/devres.h:160 [inline], CPU#0: syz.1.6464/25993
> WARNING: ./include/linux/device/devres.h:160 at devm_cxl_dpa_release drivers/cxl/core/hdm.c:290 [inline], CPU#0: syz.1.6464/25993
> WARNING: ./include/linux/device/devres.h:160 at cxl_dpa_free+0x2a4/0x320 drivers/cxl/core/hdm.c:572, CPU#0: syz.1.6464/25993
> Modules linked in:
> CPU: 0 UID: 0 PID: 25993 Comm: syz.1.6464 Not tainted 6.19.0-g15a37b05f387 #10 PREEMPT(lazy)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014
> RIP: 0010:devm_remove_action include/linux/device/devres.h:160 [inline]
> RIP: 0010:devm_cxl_dpa_release drivers/cxl/core/hdm.c:290 [inline]
> RIP: 0010:cxl_dpa_free+0x2a4/0x320 drivers/cxl/core/hdm.c:572
> Code: 01 31 ff 41 89 c4 89 c6 e8 a9 91 1d fe 45 85 e4 0f 85 55 ff ff ff e8 4b 96 1d fe 90 0f 0b 90 e9 47 ff ff ff e8 3d 96 1d fe 90 <0f> 0b 90 e9 63 ff ff ff bb f0 ff ff ff e9 68 ff ff ff 48 c7 c7 f4
> RSP: 0018:ffff888129f77bb8 EFLAGS: 00010282
> RAX: 00000000000000f3 RBX: ffff888102f64000 RCX: ffffffff837301d3
> RDX: 0000000000080000 RSI: ffffc90001c5a000 RDI: 0000000000000005
> RBP: 00000000fffffffe R08: 0000000000000001 R09: ffff888123f98000
> R10: 00000000fffffffe R11: 0000000000000000 R12: 0000000000000001
> R13: ffff888102f64040 R14: dffffc0000000000 R15: ffff888102f64000
> FS: 00007fae0488d6c0(0000) GS:ffff88827086d000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000000 CR3: 000000012f7d6003 CR4: 0000000000770ef0
> PKRU: 80000000
> Call Trace:
> <TASK>
> dpa_size_store+0xfb/0x230 drivers/cxl/core/port.c:269
> dev_attr_store+0x58/0x80 drivers/base/core.c:2437
> sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
> kernfs_fop_write_iter+0x3d6/0x5d0 fs/kernfs/file.c:352
> new_sync_write fs/read_write.c:595 [inline]
> vfs_write+0x68e/0x1050 fs/read_write.c:688
> ksys_write+0x12a/0x250 fs/read_write.c:740
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xfc/0x670 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fae0399c669
> Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fae0488d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 00007fae03c15fa0 RCX: 00007fae0399c669
> RDX: 000000000000000a RSI: 00002000000001c0 RDI: 0000000000000009
> RBP: 00007fae03a32c71 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fae03c16038 R14: 00007fae03c15fa0 R15: 00007ffe53519fb8
> </TASK>
> irq event stamp: 1021
> hardirqs last enabled at (1029): [<ffffffffb7d04c4b>] __up_console_sem+0x7b/0x90 kernel/printk/printk.c:347
> hardirqs last disabled at (1038): [<ffffffffb7d04c30>] __up_console_sem+0x60/0x90 kernel/printk/printk.c:345
> softirqs last enabled at (1016): [<ffffffffb7b73b93>] __do_softirq kernel/softirq.c:656 [inline]
> softirqs last enabled at (1016): [<ffffffffb7b73b93>] invoke_softirq kernel/softirq.c:496 [inline]
> softirqs last enabled at (1016): [<ffffffffb7b73b93>] __irq_exit_rcu+0xb3/0xe0 kernel/softirq.c:723
> softirqs last disabled at (1005): [<ffffffffb7b73b93>] __do_softirq kernel/softirq.c:656 [inline]
> softirqs last disabled at (1005): [<ffffffffb7b73b93>] invoke_softirq kernel/softirq.c:496 [inline]
> softirqs last disabled at (1005): [<ffffffffb7b73b93>] __irq_exit_rcu+0xb3/0xe0 kernel/softirq.c:723
>
> Fixes: cf880423b6a0 ("cxl/hdm: Add support for allocating DPA to an endpoint decoder")
> Fixes: 9c57cde0dcbd ("cxl/hdm: Enumerate allocated DPA")
> Signed-off-by: Sungwoo Kim <iam@sung-woo.kim>
Good find!
However I am not a fan of the fact that this duplicates this subtle
dance in multiple places. It looks like we can just make it by the case
that __cxl_dpa_reserve() establishes the remove action before returning.
> @@ -679,11 +686,28 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size)
> struct cxl_port *port = cxled_to_port(cxled);
> int rc;
>
> + guard(rwsem_write)(&cxl_rwsem.dpa);
> rc = __cxl_dpa_alloc(cxled, size);
> if (rc)
> return rc;
>
> - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
> + /*
> + * Add the devres action while still holding cxl_rwsem.dpa to prevent
> + * a race with cxl_dpa_free(). Without this, a concurrent cxl_dpa_free()
> + * can observe dpa_res set (by __cxl_dpa_reserve()) and attempt
> + * devm_remove_action() before devm_add_action() has been called,
> + * triggering a WARN_ON in devm_remove_action().
> + * Also, devm_add_action_or_reset() cannot be used here because
> + * cxl_dpa_release() tries to hold the dpa lock that is already held,
> + * causing a self deadlock.
> + */
Also, I agree with Alison, this is good detail, but way too much detail
to carry around permanently in the source directly.
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH] cxl/hdm: fix a warning in devm_remove_action()
2026-03-25 1:34 ` Dan Williams
@ 2026-03-25 3:47 ` Sungwoo Kim
0 siblings, 0 replies; 8+ messages in thread
From: Sungwoo Kim @ 2026-03-25 3:47 UTC (permalink / raw)
To: Dan Williams
Cc: Davidlohr Bueso, Jonathan Cameron, Dave Jiang, Alison Schofield,
Vishal Verma, Ira Weiny, Ben Widawsky, Dave Tian, linux-cxl,
linux-kernel
On Tue, Mar 24, 2026 at 9:35 PM Dan Williams <dan.j.williams@intel.com> wrote:
>
> Sungwoo Kim wrote:
> > In the following race scenario, devm_remove_action() can be called
> > before devm_add_action(), triggering a warning because there is no
> > action to remove.
> >
> > To fix this, extend a critical section to embrace both
> > __cxl_dpa_reserve() and devm_add_action().
> >
> > task 1:
> > cxl_dpa_alloc()
> > __cxl_dpa_reserve() ...(1)
> > devm_add_action() ...(4)
> >
> > task 2:
> > cxl_dpa_free()
> > guard()
> > if (!cxled->dpa_res) ...(2) pass, due to (1)
> > return 0;
> > devm_cxl_dpa_release()
> > devm_remove_action() ...(3) warning, no action is added yet
> >
> > Warning log:
> >
> > WARNING: ./include/linux/device/devres.h:160 at devm_remove_action include/linux/device/devres.h:160 [inline], CPU#0: syz.1.6464/25993
> > WARNING: ./include/linux/device/devres.h:160 at devm_cxl_dpa_release drivers/cxl/core/hdm.c:290 [inline], CPU#0: syz.1.6464/25993
> > WARNING: ./include/linux/device/devres.h:160 at cxl_dpa_free+0x2a4/0x320 drivers/cxl/core/hdm.c:572, CPU#0: syz.1.6464/25993
> > Modules linked in:
> > CPU: 0 UID: 0 PID: 25993 Comm: syz.1.6464 Not tainted 6.19.0-g15a37b05f387 #10 PREEMPT(lazy)
> > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014
> > RIP: 0010:devm_remove_action include/linux/device/devres.h:160 [inline]
> > RIP: 0010:devm_cxl_dpa_release drivers/cxl/core/hdm.c:290 [inline]
> > RIP: 0010:cxl_dpa_free+0x2a4/0x320 drivers/cxl/core/hdm.c:572
> > Code: 01 31 ff 41 89 c4 89 c6 e8 a9 91 1d fe 45 85 e4 0f 85 55 ff ff ff e8 4b 96 1d fe 90 0f 0b 90 e9 47 ff ff ff e8 3d 96 1d fe 90 <0f> 0b 90 e9 63 ff ff ff bb f0 ff ff ff e9 68 ff ff ff 48 c7 c7 f4
> > RSP: 0018:ffff888129f77bb8 EFLAGS: 00010282
> > RAX: 00000000000000f3 RBX: ffff888102f64000 RCX: ffffffff837301d3
> > RDX: 0000000000080000 RSI: ffffc90001c5a000 RDI: 0000000000000005
> > RBP: 00000000fffffffe R08: 0000000000000001 R09: ffff888123f98000
> > R10: 00000000fffffffe R11: 0000000000000000 R12: 0000000000000001
> > R13: ffff888102f64040 R14: dffffc0000000000 R15: ffff888102f64000
> > FS: 00007fae0488d6c0(0000) GS:ffff88827086d000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000000000000000 CR3: 000000012f7d6003 CR4: 0000000000770ef0
> > PKRU: 80000000
> > Call Trace:
> > <TASK>
> > dpa_size_store+0xfb/0x230 drivers/cxl/core/port.c:269
> > dev_attr_store+0x58/0x80 drivers/base/core.c:2437
> > sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
> > kernfs_fop_write_iter+0x3d6/0x5d0 fs/kernfs/file.c:352
> > new_sync_write fs/read_write.c:595 [inline]
> > vfs_write+0x68e/0x1050 fs/read_write.c:688
> > ksys_write+0x12a/0x250 fs/read_write.c:740
> > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> > do_syscall_64+0xfc/0x670 arch/x86/entry/syscall_64.c:94
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > RIP: 0033:0x7fae0399c669
> > Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007fae0488d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> > RAX: ffffffffffffffda RBX: 00007fae03c15fa0 RCX: 00007fae0399c669
> > RDX: 000000000000000a RSI: 00002000000001c0 RDI: 0000000000000009
> > RBP: 00007fae03a32c71 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> > R13: 00007fae03c16038 R14: 00007fae03c15fa0 R15: 00007ffe53519fb8
> > </TASK>
> > irq event stamp: 1021
> > hardirqs last enabled at (1029): [<ffffffffb7d04c4b>] __up_console_sem+0x7b/0x90 kernel/printk/printk.c:347
> > hardirqs last disabled at (1038): [<ffffffffb7d04c30>] __up_console_sem+0x60/0x90 kernel/printk/printk.c:345
> > softirqs last enabled at (1016): [<ffffffffb7b73b93>] __do_softirq kernel/softirq.c:656 [inline]
> > softirqs last enabled at (1016): [<ffffffffb7b73b93>] invoke_softirq kernel/softirq.c:496 [inline]
> > softirqs last enabled at (1016): [<ffffffffb7b73b93>] __irq_exit_rcu+0xb3/0xe0 kernel/softirq.c:723
> > softirqs last disabled at (1005): [<ffffffffb7b73b93>] __do_softirq kernel/softirq.c:656 [inline]
> > softirqs last disabled at (1005): [<ffffffffb7b73b93>] invoke_softirq kernel/softirq.c:496 [inline]
> > softirqs last disabled at (1005): [<ffffffffb7b73b93>] __irq_exit_rcu+0xb3/0xe0 kernel/softirq.c:723
> >
> > Fixes: cf880423b6a0 ("cxl/hdm: Add support for allocating DPA to an endpoint decoder")
> > Fixes: 9c57cde0dcbd ("cxl/hdm: Enumerate allocated DPA")
> > Signed-off-by: Sungwoo Kim <iam@sung-woo.kim>
>
> Good find!
>
> However I am not a fan of the fact that this duplicates this subtle
> dance in multiple places. It looks like we can just make it by the case
> that __cxl_dpa_reserve() establishes the remove action before returning.
This also makes sense to me. Then, we need to change __cxl_dpa_alloc()
in the same way. Will do in V2.
Other than those two, I can find other functions that likely have the
same bug, such as devm_cxl_add_dax_region(), which might race with
cxl_dax_region_release(). To confirm, I'll try to trigger bugs in
these suspicious functions and see if they are indeed buggy.
>
> > @@ -679,11 +686,28 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size)
> > struct cxl_port *port = cxled_to_port(cxled);
> > int rc;
> >
> > + guard(rwsem_write)(&cxl_rwsem.dpa);
> > rc = __cxl_dpa_alloc(cxled, size);
> > if (rc)
> > return rc;
> >
> > - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
> > + /*
> > + * Add the devres action while still holding cxl_rwsem.dpa to prevent
> > + * a race with cxl_dpa_free(). Without this, a concurrent cxl_dpa_free()
> > + * can observe dpa_res set (by __cxl_dpa_reserve()) and attempt
> > + * devm_remove_action() before devm_add_action() has been called,
> > + * triggering a WARN_ON in devm_remove_action().
> > + * Also, devm_add_action_or_reset() cannot be used here because
> > + * cxl_dpa_release() tries to hold the dpa lock that is already held,
> > + * causing a self deadlock.
> > + */
>
> Also, I agree with Alison, this is good detail, but way too much detail
> to carry around permanently in the source directly.
>
I will shrink it down. Thanks for the comments.
Sungwoo.
^ permalink raw reply [flat|nested] 8+ messages in thread