[syzbot] [mm?] [hfs?] KASAN: slab-out-of-bounds Read in generic_perform_write

[syzbot] [mm?] [hfs?] KASAN: slab-out-of-bounds Read in generic_perform_write

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    2cf0f7156238 Merge tag 'nfs-for-6.6-2' of git://git.linux-..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=153cd286680000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e4ca82a1bedd37e4
dashboard link: https://syzkaller.appspot.com/bug?extid=4a2376bc62e59406c414
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11e88918680000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10aea78c680000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/eac482f1f6bc/disk-2cf0f715.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7a69dad9f1ff/vmlinux-2cf0f715.xz
kernel image: https://storage.googleapis.com/syzbot-assets/16676b650375/bzImage-2cf0f715.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/c040f8fc7107/mount_0.gz

Bisection is inconclusive: the issue happens on the oldest tested release.

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10e0a282680000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=12e0a282680000
console output: https://syzkaller.appspot.com/x/log.txt?x=14e0a282680000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4a2376bc62e59406c414@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in memcpy_from_iter lib/iov_iter.c:380 [inline]
BUG: KASAN: slab-out-of-bounds in copy_page_from_iter_atomic+0x908/0x12f0 lib/iov_iter.c:590
Read of size 1024 at addr ffff888020b4ec00 by task kworker/u4:7/1273

CPU: 0 PID: 1273 Comm: kworker/u4:7 Not tainted 6.6.0-rc2-syzkaller-00018-g2cf0f7156238 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/04/2023
Workqueue: loop0 loop_rootcg_workfn
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:364 [inline]
 print_report+0x163/0x540 mm/kasan/report.c:475
 kasan_report+0x175/0x1b0 mm/kasan/report.c:588
 kasan_check_range+0x27e/0x290 mm/kasan/generic.c:187
 __asan_memcpy+0x29/0x70 mm/kasan/shadow.c:105
 memcpy_from_iter lib/iov_iter.c:380 [inline]
 copy_page_from_iter_atomic+0x908/0x12f0 lib/iov_iter.c:590
 generic_perform_write+0x392/0x630 mm/filemap.c:3950
 shmem_file_write_iter+0xfc/0x120 mm/shmem.c:2865
 do_iter_write+0x84f/0xde0 fs/read_write.c:860
 lo_write_bvec drivers/block/loop.c:249 [inline]
 lo_write_simple drivers/block/loop.c:271 [inline]
 do_req_filebacked drivers/block/loop.c:495 [inline]
 loop_handle_cmd drivers/block/loop.c:1915 [inline]
 loop_process_work+0x14c3/0x22a0 drivers/block/loop.c:1950
 process_one_work kernel/workqueue.c:2630 [inline]
 process_scheduled_works+0x90f/0x1400 kernel/workqueue.c:2703
 worker_thread+0xa5f/0xff0 kernel/workqueue.c:2784
 kthread+0x2d3/0x370 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304
 </TASK>

Allocated by task 5038:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4f/0x70 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:374 [inline]
 __kasan_kmalloc+0x98/0xb0 mm/kasan/common.c:383
 kasan_kmalloc include/linux/kasan.h:198 [inline]
 __do_kmalloc_node mm/slab_common.c:1023 [inline]
 __kmalloc+0xb9/0x230 mm/slab_common.c:1036
 kmalloc include/linux/slab.h:603 [inline]
 hfsplus_read_wrapper+0x545/0x1330 fs/hfsplus/wrapper.c:178
 hfsplus_fill_super+0x38e/0x1c90 fs/hfsplus/super.c:413
 mount_bdev+0x237/0x300 fs/super.c:1629
 legacy_get_tree+0xef/0x190 fs/fs_context.c:638
 vfs_get_tree+0x8c/0x280 fs/super.c:1750
 do_new_mount+0x28f/0xae0 fs/namespace.c:3335
 do_mount fs/namespace.c:3675 [inline]
 __do_sys_mount fs/namespace.c:3884 [inline]
 __se_sys_mount+0x2d9/0x3c0 fs/namespace.c:3861
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

The buggy address belongs to the object at ffff888020b4ec00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 allocated 512-byte region [ffff888020b4ec00, ffff888020b4ee00)

The buggy address belongs to the physical page:
page:ffffea000082d300 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x20b4c
head:ffffea000082d300 order:2 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888012841c80 ffffea000085e900 dead000000000002
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 12443144717, free_ts 0
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1e6/0x210 mm/page_alloc.c:1536
 prep_new_page mm/page_alloc.c:1543 [inline]
 get_page_from_freelist+0x31db/0x3360 mm/page_alloc.c:3170
 __alloc_pages+0x255/0x670 mm/page_alloc.c:4426
 alloc_page_interleave+0x22/0x1d0 mm/mempolicy.c:2131
 alloc_slab_page+0x6a/0x160 mm/slub.c:1870
 allocate_slab mm/slub.c:2017 [inline]
 new_slab+0x84/0x2f0 mm/slub.c:2070
 ___slab_alloc+0xc85/0x1310 mm/slub.c:3223
 __slab_alloc mm/slub.c:3322 [inline]
 __slab_alloc_node mm/slub.c:3375 [inline]
 slab_alloc_node mm/slub.c:3468 [inline]
 __kmem_cache_alloc_node+0x1af/0x270 mm/slub.c:3517
 kmalloc_trace+0x2a/0xe0 mm/slab_common.c:1114
 kmalloc include/linux/slab.h:599 [inline]
 kzalloc include/linux/slab.h:720 [inline]
 dev_pm_qos_constraints_allocate+0x8f/0x400 drivers/base/power/qos.c:204
 __dev_pm_qos_add_request+0x121/0x4a0 drivers/base/power/qos.c:344
 dev_pm_qos_add_request+0x3a/0x60 drivers/base/power/qos.c:394
 usb_hub_create_port_device+0x4c6/0xc40 drivers/usb/core/port.c:727
 hub_configure drivers/usb/core/hub.c:1685 [inline]
 hub_probe+0x2469/0x3570 drivers/usb/core/hub.c:1922
 usb_probe_interface+0x5c4/0xb00 drivers/usb/core/driver.c:396
 really_probe+0x294/0xc30 drivers/base/dd.c:658
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888020b4ed00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888020b4ed80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888020b4ee00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                   ^
 ffff888020b4ee80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888020b4ef00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the bug is already fixed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite bug's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the bug is a duplicate of another bug, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[PATCH] fs/hfsplus: expand s_vhdr_buf size to avoid slab oob

[Edward AD]

The memory allocated to s_vhdr_buf in the function hfsplus-read_wrapper is 
too small, resulting in a slab out of bounds issue when copying data with 
copy_page_from_iter_atomic.

When allocating memory to s_vhdr_buf, take the maximum value between 
hfsplus_min_io_size(sb) and PAGE_SIZE to avoid similar issues.

Reported-and-tested-by: syzbot+4a2376bc62e59406c414@syzkaller.appspotmail.com
Signed-off-by: Edward AD <twuufnxlz@gmail.com>
---
 fs/hfsplus/wrapper.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/hfsplus/wrapper.c b/fs/hfsplus/wrapper.c
index 0b791adf02e5..56bee8dbe532 100644
--- a/fs/hfsplus/wrapper.c
+++ b/fs/hfsplus/wrapper.c
@@ -163,7 +163,7 @@ int hfsplus_read_wrapper(struct super_block *sb)
 	struct hfsplus_sb_info *sbi = HFSPLUS_SB(sb);
 	struct hfsplus_wd wd;
 	sector_t part_start, part_size;
-	u32 blocksize;
+	u32 blocksize, bufsize;
 	int error = 0;
 
 	error = -EINVAL;
@@ -175,10 +175,11 @@ int hfsplus_read_wrapper(struct super_block *sb)
 		goto out;
 
 	error = -ENOMEM;
-	sbi->s_vhdr_buf = kmalloc(hfsplus_min_io_size(sb), GFP_KERNEL);
+	bufsize = max_t(u32, hfsplus_min_io_size(sb), PAGE_SIZE);
+	sbi->s_vhdr_buf = kmalloc(bufsize, GFP_KERNEL);
 	if (!sbi->s_vhdr_buf)
 		goto out;
-	sbi->s_backup_vhdr_buf = kmalloc(hfsplus_min_io_size(sb), GFP_KERNEL);
+	sbi->s_backup_vhdr_buf = kmalloc(bufsize, GFP_KERNEL);
 	if (!sbi->s_backup_vhdr_buf)
 		goto out_free_vhdr;
 
-- 
2.25.1

Re: [syzbot] Test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: Test
Author: tintinm2017@gmail.com

#syz test:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Re: [PATCH] fs/hfsplus: expand s_vhdr_buf size to avoid slab oob

[Dmitry Vyukov]

Hi Edward,

Was this patch lost? I don't see it merged anywhere.
This bug is still present in most kernels out there.

Re: [syzbot] [hfs?] [mm?] KASAN: slab-out-of-bounds Read in generic_perform_write

[syzbot]

syzbot suspects this issue was fixed by commit:

commit b432163ebd15a0fb74051949cb61456d6c55ccbd
Author: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
Date:   Thu Jan 30 14:03:41 2025 +0000

    fs/ntfs3: Update inode->i_mapping->a_ops on compression state

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=115c5b68580000
start commit:   fc033cf25e61 Linux 6.13-rc5
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=ba7cde9482d6bb6
dashboard link: https://syzkaller.appspot.com/bug?extid=4a2376bc62e59406c414
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1654aac4580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13ff26df980000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: fs/ntfs3: Update inode->i_mapping->a_ops on compression state

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: [syzbot] test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: test
Author: danielyangkang@gmail.com

#syz test

Re: [syzbot] test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: test
Author: danielyangkang@gmail.com

#syz test

Re: [syzbot] Test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test 

---
 include/linux/sched.h |  7 +++++++
 kernel/sched/core.c   |  1 +
 kernel/sched/rt.c     | 26 +++++++++++++++++++++++---
 kernel/signal.c       |  9 +++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 17cb0761ff65..123bc16ad3d0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1121,6 +1121,13 @@ struct task_struct {
 	size_t				sas_ss_size;
 	unsigned int			sas_ss_flags;
 
+	/*
+	 * Number of signals received by an RT task between scheduling ticks.
+	 * This counter is used to throttle RT tasks when too many signals
+	 * (e.g., POSIX timers) are sent to the task, which can cause an RCU stall.
+	 */
+	atomic_t rt_signals_recv_count; /* used outside of the rq lock */
+
 	struct callback_head		*task_works;
 
 #ifdef CONFIG_AUDIT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d44efa0d0611..9def826bd35f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4779,6 +4779,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 			p->policy = SCHED_NORMAL;
 			p->static_prio = NICE_TO_PRIO(0);
 			p->rt_priority = 0;
+			atomic_set(&p->rt_signals_recv_count, 0);
 		} else if (PRIO_TO_NICE(p->static_prio) < 0)
 			p->static_prio = NICE_TO_PRIO(0);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..9b22d67d1746 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -24,6 +24,15 @@ int sysctl_sched_rt_period = 1000000;
  */
 int sysctl_sched_rt_runtime = 950000;
 
+/*
+ * To avoid an RCU stall due to a large number of signals received by RT tasks
+ * (e.g., POSIX timers), the RT task needs to be throttled.
+ * When the number of signals received by an RT task during a scheduling
+ * tick period exceeds the threshold, the RT task will be throttled.
+ * The value of 100 has not been thoroughly tested and may need adjustment.
+ */
+#define RT_RECV_SGINAL_THROTTLE_THRESHOLD 100
+
 #ifdef CONFIG_SYSCTL
 static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC * RR_TIMESLICE) / HZ;
 static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
@@ -951,7 +960,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
-static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, int rt_signal_recv)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
 
@@ -966,7 +975,15 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 	if (runtime == RUNTIME_INF)
 		return 0;
 
-	if (rt_rq->rt_time > runtime) {
+	/*
+	 * When a large number of signals are sent to this task (e.g., POSIX timers)
+	 * the delta time deviates significantly from real time due to the overhead
+	 * of handling signals. For RT tasks, this can cause an RCU stall.
+	 * To avoid this, throttle the task when the number of signals received
+	 * exceeds a certain threshold.
+	 */
+	if (rt_rq->rt_time > runtime ||
+		rt_signal_recv >= RT_RECV_SGINAL_THROTTLE_THRESHOLD) {
 		struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
 
 		/*
@@ -1021,7 +1038,9 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			exceeded = sched_rt_runtime_exceeded(rt_rq);
+			exceeded = sched_rt_runtime_exceeded(
+						rt_rq,
+						atomic_read(&curr->rt_signals_recv_count));
 			if (exceeded)
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
@@ -1029,6 +1048,7 @@ static void update_curr_rt(struct rq *rq)
 				do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
 		}
 	}
+	atomic_set(&curr->rt_signals_recv_count, 0);
 }
 
 static void
diff --git a/kernel/signal.c b/kernel/signal.c
index bdca529f0f7b..d58e0ba9336c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -629,6 +629,15 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
 	bool resched_timer = false;
 	int signr;
 
+	/*
+	 * To prevent an RCU stall due to receiving too many signals by RT tasks,
+	 * count all signals regardless of their type.
+	 * Based on this counter, the RT scheduler will decide whether the task
+	 * should be throttled or not.
+	 */
+	if (tsk->policy == SCHED_FIFO || tsk->policy == SCHED_RR)
+		atomic_inc(&tsk->rt_signals_recv_count);
+
 	/* We only dequeue private signals from ourselves, we don't let
 	 * signalfd steal them
 	 */
-- 
2.43.0

Re: [syzbot] Test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git dccb07f2914cdab2ac3a5b6c98406f765acab803

---
 include/linux/sched.h |  7 +++++++
 kernel/sched/core.c   |  1 +
 kernel/sched/rt.c     | 26 +++++++++++++++++++++++---
 kernel/signal.c       |  9 +++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 17cb0761ff65..123bc16ad3d0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1121,6 +1121,13 @@ struct task_struct {
 	size_t				sas_ss_size;
 	unsigned int			sas_ss_flags;
 
+	/*
+	 * Number of signals received by an RT task between scheduling ticks.
+	 * This counter is used to throttle RT tasks when too many signals
+	 * (e.g., POSIX timers) are sent to the task, which can cause an RCU stall.
+	 */
+	atomic_t rt_signals_recv_count; /* used outside of the rq lock */
+
 	struct callback_head		*task_works;
 
 #ifdef CONFIG_AUDIT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d44efa0d0611..9def826bd35f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4779,6 +4779,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 			p->policy = SCHED_NORMAL;
 			p->static_prio = NICE_TO_PRIO(0);
 			p->rt_priority = 0;
+			atomic_set(&p->rt_signals_recv_count, 0);
 		} else if (PRIO_TO_NICE(p->static_prio) < 0)
 			p->static_prio = NICE_TO_PRIO(0);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..9b22d67d1746 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -24,6 +24,15 @@ int sysctl_sched_rt_period = 1000000;
  */
 int sysctl_sched_rt_runtime = 950000;
 
+/*
+ * To avoid an RCU stall due to a large number of signals received by RT tasks
+ * (e.g., POSIX timers), the RT task needs to be throttled.
+ * When the number of signals received by an RT task during a scheduling
+ * tick period exceeds the threshold, the RT task will be throttled.
+ * The value of 100 has not been thoroughly tested and may need adjustment.
+ */
+#define RT_RECV_SGINAL_THROTTLE_THRESHOLD 100
+
 #ifdef CONFIG_SYSCTL
 static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC * RR_TIMESLICE) / HZ;
 static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
@@ -951,7 +960,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
-static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, int rt_signal_recv)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
 
@@ -966,7 +975,15 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 	if (runtime == RUNTIME_INF)
 		return 0;
 
-	if (rt_rq->rt_time > runtime) {
+	/*
+	 * When a large number of signals are sent to this task (e.g., POSIX timers)
+	 * the delta time deviates significantly from real time due to the overhead
+	 * of handling signals. For RT tasks, this can cause an RCU stall.
+	 * To avoid this, throttle the task when the number of signals received
+	 * exceeds a certain threshold.
+	 */
+	if (rt_rq->rt_time > runtime ||
+		rt_signal_recv >= RT_RECV_SGINAL_THROTTLE_THRESHOLD) {
 		struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
 
 		/*
@@ -1021,7 +1038,9 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			exceeded = sched_rt_runtime_exceeded(rt_rq);
+			exceeded = sched_rt_runtime_exceeded(
+						rt_rq,
+						atomic_read(&curr->rt_signals_recv_count));
 			if (exceeded)
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
@@ -1029,6 +1048,7 @@ static void update_curr_rt(struct rq *rq)
 				do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
 		}
 	}
+	atomic_set(&curr->rt_signals_recv_count, 0);
 }
 
 static void
diff --git a/kernel/signal.c b/kernel/signal.c
index bdca529f0f7b..d58e0ba9336c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -629,6 +629,15 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
 	bool resched_timer = false;
 	int signr;
 
+	/*
+	 * To prevent an RCU stall due to receiving too many signals by RT tasks,
+	 * count all signals regardless of their type.
+	 * Based on this counter, the RT scheduler will decide whether the task
+	 * should be throttled or not.
+	 */
+	if (tsk->policy == SCHED_FIFO || tsk->policy == SCHED_RR)
+		atomic_inc(&tsk->rt_signals_recv_count);
+
 	/* We only dequeue private signals from ourselves, we don't let
 	 * signalfd steal them
 	 */
-- 
2.43.0

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Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git fe46a7dd189e25604716c03576d05ac8a5209743

---
 include/linux/sched.h |  7 +++++++
 kernel/sched/core.c   |  1 +
 kernel/sched/rt.c     | 26 +++++++++++++++++++++++---
 kernel/signal.c       |  9 +++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 17cb0761ff65..123bc16ad3d0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1121,6 +1121,13 @@ struct task_struct {
 	size_t				sas_ss_size;
 	unsigned int			sas_ss_flags;
 
+	/*
+	 * Number of signals received by an RT task between scheduling ticks.
+	 * This counter is used to throttle RT tasks when too many signals
+	 * (e.g., POSIX timers) are sent to the task, which can cause an RCU stall.
+	 */
+	atomic_t rt_signals_recv_count; /* used outside of the rq lock */
+
 	struct callback_head		*task_works;
 
 #ifdef CONFIG_AUDIT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d44efa0d0611..9def826bd35f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4779,6 +4779,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 			p->policy = SCHED_NORMAL;
 			p->static_prio = NICE_TO_PRIO(0);
 			p->rt_priority = 0;
+			atomic_set(&p->rt_signals_recv_count, 0);
 		} else if (PRIO_TO_NICE(p->static_prio) < 0)
 			p->static_prio = NICE_TO_PRIO(0);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..9b22d67d1746 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -24,6 +24,15 @@ int sysctl_sched_rt_period = 1000000;
  */
 int sysctl_sched_rt_runtime = 950000;
 
+/*
+ * To avoid an RCU stall due to a large number of signals received by RT tasks
+ * (e.g., POSIX timers), the RT task needs to be throttled.
+ * When the number of signals received by an RT task during a scheduling
+ * tick period exceeds the threshold, the RT task will be throttled.
+ * The value of 100 has not been thoroughly tested and may need adjustment.
+ */
+#define RT_RECV_SGINAL_THROTTLE_THRESHOLD 100
+
 #ifdef CONFIG_SYSCTL
 static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC * RR_TIMESLICE) / HZ;
 static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
@@ -951,7 +960,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
-static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, int rt_signal_recv)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
 
@@ -966,7 +975,15 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 	if (runtime == RUNTIME_INF)
 		return 0;
 
-	if (rt_rq->rt_time > runtime) {
+	/*
+	 * When a large number of signals are sent to this task (e.g., POSIX timers)
+	 * the delta time deviates significantly from real time due to the overhead
+	 * of handling signals. For RT tasks, this can cause an RCU stall.
+	 * To avoid this, throttle the task when the number of signals received
+	 * exceeds a certain threshold.
+	 */
+	if (rt_rq->rt_time > runtime ||
+		rt_signal_recv >= RT_RECV_SGINAL_THROTTLE_THRESHOLD) {
 		struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
 
 		/*
@@ -1021,7 +1038,9 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			exceeded = sched_rt_runtime_exceeded(rt_rq);
+			exceeded = sched_rt_runtime_exceeded(
+						rt_rq,
+						atomic_read(&curr->rt_signals_recv_count));
 			if (exceeded)
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
@@ -1029,6 +1048,7 @@ static void update_curr_rt(struct rq *rq)
 				do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
 		}
 	}
+	atomic_set(&curr->rt_signals_recv_count, 0);
 }
 
 static void
diff --git a/kernel/signal.c b/kernel/signal.c
index bdca529f0f7b..d58e0ba9336c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -629,6 +629,15 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
 	bool resched_timer = false;
 	int signr;
 
+	/*
+	 * To prevent an RCU stall due to receiving too many signals by RT tasks,
+	 * count all signals regardless of their type.
+	 * Based on this counter, the RT scheduler will decide whether the task
+	 * should be throttled or not.
+	 */
+	if (tsk->policy == SCHED_FIFO || tsk->policy == SCHED_RR)
+		atomic_inc(&tsk->rt_signals_recv_count);
+
 	/* We only dequeue private signals from ourselves, we don't let
 	 * signalfd steal them
 	 */
-- 
2.43.0

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#syz test:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

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Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 71b1543c83d65af8215d7558d70fc2ecbee77dcf

---
 net/sched/sch_taprio.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index a0d54b422186..41add4a1d407 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -44,6 +44,8 @@ static struct static_key_false taprio_have_working_mqprio;
 	(TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST | TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD)
 #define TAPRIO_FLAGS_INVALID U32_MAX
 
+#define TAPRIO_MAX_NUM_SCHEDULES_BEFORE_NOW 10
+
 struct sched_entry {
 	/* Durations between this GCL entry and the GCL entry where the
 	 * respective traffic class gate closes
@@ -62,6 +64,8 @@ struct sched_entry {
 	u32 gate_mask;
 	u32 interval;
 	u8 command;
+	/* Used to skip some cycles to prevent other tasks from starving */
+	u8 num_schedules_before_now;
 };
 
 struct sched_gate_list {
@@ -111,6 +115,9 @@ struct __tc_taprio_qopt_offload {
 	struct tc_taprio_qopt_offload offload;
 };
 
+static void setup_txtime(struct taprio_sched *q,
+			 struct sched_gate_list *sched, ktime_t base);
+
 static void taprio_calculate_gate_durations(struct taprio_sched *q,
 					    struct sched_gate_list *sched)
 {
@@ -919,6 +926,7 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
 	struct sched_entry *entry, *next;
 	struct Qdisc *sch = q->root;
 	ktime_t end_time;
+	ktime_t basenow;
 	int tc;
 
 	spin_lock(&q->current_entry_lock);
@@ -977,6 +985,23 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
 	taprio_set_budgets(q, oper, next);
 
 first_run:
+	basenow = ktime_get();
+	if (ktime_before(end_time, basenow))
+	{
+		next->num_schedules_before_now++;
+		if (next->num_schedules_before_now >= TAPRIO_MAX_NUM_SCHEDULES_BEFORE_NOW)
+		{
+			end_time = ktime_add_ns(basenow, oper->cycle_time);
+			next->end_time = end_time;
+			next->num_schedules_before_now = 0;
+			setup_txtime(q, oper, basenow);
+		}
+	}
+	else
+	{
+		next->num_schedules_before_now = 0;
+	}
+
 	rcu_assign_pointer(q->current_entry, next);
 	spin_unlock(&q->current_entry_lock);
 
@@ -1074,6 +1099,7 @@ static int parse_sched_entry(struct taprio_sched *q, struct nlattr *n,
 	}
 
 	entry->index = index;
+	entry->num_schedules_before_now = 0;
 
 	return fill_sched_entry(q, tb, entry, extack);
 }
-- 
2.43.0

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