[PATCH] erofs: Fix detection of atomic context to prevent sleeping in invalid context

[Junli Liu]

From: Junli liu <liujunli at lixiang.com>

The current atomic context detection is insufficient and can lead to
sleeping function calls in invalid contexts, causing kernel warnings
and potential system instability. See the stacktrace [1]

The current implementation only checks rcu_read_lock_any_held(), which
behaves inconsistently across different kernel configurations:

- When CONFIG_DEBUG_LOCK_ALLOC is enabled: correctly detects RCU critical
  sections by checking rcu_lock_map
- When CONFIG_DEBUG_LOCK_ALLOC is disabled: compiles to "!preemptible()",
  which only checks preempt_count and misses RCU critical sections

This patch introduces z_erofs_in_atomic() to provide comprehensive atomic
context detection:

1. Check RCU preemption depth when CONFIG_PREEMPTION is enabled, as RCU
   critical sections may not affect preempt_count but still require
   atomic handling

2. Always use async processing when CONFIG_PREEMPT_COUNT is disabled,
   as preemption state cannot be reliably determined

3. Fall back to standard preemptible() check for remaining cases

The function replaces the previous complex condition check and ensures
that z_erofs always uses (kthread_)work in atomic contexts to minimize
scheduling overhead and prevent sleeping in invalid contexts.

==============================================
[1] Problem stacktrace
[ 61.266692] BUG: sleeping function called from invalid context at kernel/locking/rtmutex_api.c:510
[ 61.266702] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 107, name: irq/54-ufshcd
[ 61.266704] preempt_count: 0, expected: 0
[ 61.266705] RCU nest depth: 2, expected: 0
[ 61.266710] CPU: 0 UID: 0 PID: 107 Comm: irq/54-ufshcd Tainted: G W O 6.12.17 #1
[ 61.266714] Tainted: [W]=WARN, [O]=OOT_MODULE
[ 61.266715] Hardware name: schumacher (DT)
[ 61.266717] Call trace:
[ 61.266718] dump_backtrace+0x9c/0x100
[ 61.266727] show_stack+0x20/0x38
[ 61.266728] dump_stack_lvl+0x78/0x90
[ 61.266734] dump_stack+0x18/0x28
[ 61.266736] __might_resched+0x11c/0x180
[ 61.266743] __might_sleep+0x64/0xc8
[ 61.266745] mutex_lock+0x2c/0xc0
[ 61.266748] z_erofs_decompress_queue+0xe8/0x978
[ 61.266753] z_erofs_decompress_kickoff+0xa8/0x190
[ 61.266756] z_erofs_endio+0x168/0x288
[ 61.266758] bio_endio+0x160/0x218
[ 61.266762] blk_update_request+0x244/0x458
[ 61.266766] scsi_end_request+0x38/0x278
[ 61.266770] scsi_io_completion+0x4c/0x600
[ 61.266772] scsi_finish_command+0xc8/0xe8
[ 61.266775] scsi_complete+0x88/0x148
[ 61.266777] blk_mq_complete_request+0x3c/0x58
[ 61.266780] scsi_done_internal+0xcc/0x158
[ 61.266782] scsi_done+0x1c/0x30
[ 61.266783] ufshcd_compl_one_cqe+0x12c/0x438
[ 61.266786] __ufshcd_transfer_req_compl+0x2c/0x78
[ 61.266788] ufshcd_poll+0xf4/0x210
[ 61.266789] ufshcd_transfer_req_compl+0x50/0x88
[ 61.266791] ufshcd_intr+0x21c/0x7c8
[ 61.266792] irq_forced_thread_fn+0x44/0xd8
[ 61.266796] irq_thread+0x1a4/0x358
[ 61.266799] kthread+0x12c/0x138
[ 61.266802] ret_from_fork+0x10/0x20

Signed-off-by: Junli Liu <liujunli at lixiang.com>
---
 fs/erofs/zdata.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 792f20888..1883781c9 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1432,6 +1432,16 @@ static void z_erofs_decompressqueue_kthread_work(struct kthread_work *work)
 }
 #endif
 
+/* Use (kthread_)work in atomic contexts to minimize scheduling overhead */
+static inline bool z_erofs_in_atomic(void)
+{
+	if (IS_ENABLED(CONFIG_PREEMPTION) && rcu_preempt_depth())
+		return true;
+	if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
+		return true;
+	return !preemptible();
+}
+
 static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
 				       int bios)
 {
@@ -1446,8 +1456,8 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
 
 	if (atomic_add_return(bios, &io->pending_bios))
 		return;
-	/* Use (kthread_)work and sync decompression for atomic contexts only */
-	if (!in_task() || irqs_disabled() || rcu_read_lock_any_held()) {
+
+	if (z_erofs_in_atomic()) {
 #ifdef CONFIG_EROFS_FS_PCPU_KTHREAD
 		struct kthread_worker *worker;
 
-- 
2.25.1

声明：这封邮件只允许文件接收者阅读，有很高的机密性要求。禁止其他人使用、打开、复制或转发里面的任何内容。如果本邮件错误地发给了你，请联系邮件发出者并删除这个文件。机密及法律的特权并不因为误发邮件而放弃或丧失。任何提出的观点或意见只属于作者的个人见解，并不一定代表本公司。
Disclaimer: This email is intended to be read only by the designated recipient of the document and has high confidentiality requirements. Anyone else is prohibited from using, opening, copying or forwarding any of the contents inside. If this email was sent to you by mistake, please contact the sender of the email and delete this file immediately. Confidentiality and legal privileges are not waived or lost by misdirected emails. Any views or opinions expressed in the email are those of the author and do not necessarily represent those of the Company.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ozlabs.org/pipermail/linux-erofs/attachments/20250804/5938cf5a/attachment.htm>