[PATCH 6.1.y] erofs: Fix detection of atomic context

[Artem Dinaburg <artem@trailofbits.com>]

From: Sandeep Dhavale <dhavale@google.com>

[ Upstream commit 12d0a24afd9ea58e581ea64d64e066f2027b28d9 ]

Current check for atomic context is not sufficient as
z_erofs_decompressqueue_endio can be called under rcu lock
from blk_mq_flush_plug_list(). See the stacktrace [1]

In such case we should hand off the decompression work for async
processing rather than trying to do sync decompression in current
context. Patch fixes the detection by checking for
rcu_read_lock_any_held() and while at it use more appropriate
!in_task() check than in_atomic().

Background: Historically erofs would always schedule a kworker for
decompression which would incur the scheduling cost regardless of
the context. But z_erofs_decompressqueue_endio() may not always
be in atomic context and we could actually benefit from doing the
decompression in z_erofs_decompressqueue_endio() if we are in
thread context, for example when running with dm-verity.
This optimization was later added in patch [2] which has shown
improvement in performance benchmarks.

==============================================
[1] Problem stacktrace
[name:core&]BUG: sleeping function called from invalid context at kernel/locking/mutex.c:291
[name:core&]in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 1615, name: CpuMonitorServi
[name:core&]preempt_count: 0, expected: 0
[name:core&]RCU nest depth: 1, expected: 0
CPU: 7 PID: 1615 Comm: CpuMonitorServi Tainted: G S      W  OE      6.1.25-android14-5-maybe-dirty-mainline #1
Hardware name: MT6897 (DT)
Call trace:
 dump_backtrace+0x108/0x15c
 show_stack+0x20/0x30
 dump_stack_lvl+0x6c/0x8c
 dump_stack+0x20/0x48
 __might_resched+0x1fc/0x308
 __might_sleep+0x50/0x88
 mutex_lock+0x2c/0x110
 z_erofs_decompress_queue+0x11c/0xc10
 z_erofs_decompress_kickoff+0x110/0x1a4
 z_erofs_decompressqueue_endio+0x154/0x180
 bio_endio+0x1b0/0x1d8
 __dm_io_complete+0x22c/0x280
 clone_endio+0xe4/0x280
 bio_endio+0x1b0/0x1d8
 blk_update_request+0x138/0x3a4
 blk_mq_plug_issue_direct+0xd4/0x19c
 blk_mq_flush_plug_list+0x2b0/0x354
 __blk_flush_plug+0x110/0x160
 blk_finish_plug+0x30/0x4c
 read_pages+0x2fc/0x370
 page_cache_ra_unbounded+0xa4/0x23c
 page_cache_ra_order+0x290/0x320
 do_sync_mmap_readahead+0x108/0x2c0
 filemap_fault+0x19c/0x52c
 __do_fault+0xc4/0x114
 handle_mm_fault+0x5b4/0x1168
 do_page_fault+0x338/0x4b4
 do_translation_fault+0x40/0x60
 do_mem_abort+0x60/0xc8
 el0_da+0x4c/0xe0
 el0t_64_sync_handler+0xd4/0xfc
 el0t_64_sync+0x1a0/0x1a4

[2] Link: https://lore.kernel.org/all/20210317035448.13921-1-huangjianan@oppo.com/

Reported-by: Will Shiu <Will.Shiu@mediatek.com>
Suggested-by: Gao Xiang <xiang@kernel.org>
Signed-off-by: Sandeep Dhavale <dhavale@google.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Link: https://lore.kernel.org/r/20230621220848.3379029-1-dhavale@google.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

[ Backport to 6.1.y: the source change is unchanged; only its location
  in z_erofs_decompress_kickoff() differs. ]
Assisted-by: LLM
Signed-off-by: Artem Dinaburg <artem@trailofbits.com>
---
Hi Greg, Sasha, and EROFS maintainers,

I am continuing backporting CVE fixes still missing from 6.1.y.
This fix is inherited by v6.6 and every later mainline release, but 6.1.y
still has the affected code. The target-specific adjustment is described
in the bracketed note above.

Could you please queue it for 6.1.y?

Thanks,
Artem Dinaburg

CVE: CVE-2023-53231

Build: This patch was included in an x86_64 allmodconfig and
CONFIG_WERROR=y build.
It produced vmlinux and modules with no new warnings or errors.

AI assistance: An LLM helped find, adapt, and validate this
backport; I reviewed the patch and test output.

 fs/erofs/zdata.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 66c323cbdd73e1..49b7c77488415a 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1271,7 +1271,7 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
 	if (atomic_add_return(bios, &io->pending_bios))
 		return;
 	/* Use workqueue and sync decompression for atomic contexts only */
-	if (in_atomic() || irqs_disabled()) {
+	if (!in_task() || irqs_disabled() || rcu_read_lock_any_held()) {
 		queue_work(z_erofs_workqueue, &io->u.work);
 		/* enable sync decompression for readahead */
 		if (sbi->opt.sync_decompress == EROFS_SYNC_DECOMPRESS_AUTO)
-- 
2.39.5