6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Junli Liu liujunli@lixiang.com
[ Upstream commit c99fab6e80b76422741d34aafc2f930a482afbdd ]
Since EROFS handles decompression in non-atomic contexts due to uncontrollable decompression latencies and vmap() usage, it tries to detect atomic contexts and only kicks off a kworker on demand in order to reduce unnecessary scheduling overhead.
However, the current approach is insufficient and can lead to sleeping function calls in invalid contexts, causing kernel warnings and potential system instability. See the stacktrace [1] and previous discussion [2].
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
[2] https://lore.kernel.org/r/58b661d0-0ebb-4b45-a10d-c5927fb791cd@paulmck-lapto...
Signed-off-by: Junli Liu liujunli@lixiang.com Reviewed-by: Gao Xiang hsiangkao@linux.alibaba.com Link: https://lore.kernel.org/r/20250805011957.911186-1-liujunli@lixiang.com [ Gao Xiang: Use the original trace in v1. ] Signed-off-by: Gao Xiang hsiangkao@linux.alibaba.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/erofs/zdata.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c index d852b43ac43e3..c1f802ecc47b2 100644 --- a/fs/erofs/zdata.c +++ b/fs/erofs/zdata.c @@ -1401,6 +1401,16 @@ 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) { @@ -1415,8 +1425,7 @@ 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;