On 2025/8/5 09:19, Junli Liu wrote:
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
BUG: sleeping function called from invalid context at
kernel/locking/rtmutex_api.c:510
in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 107,
name: irq/54-ufshcd
preempt_count: 0, expected: 0
RCU nest depth: 2, expected: 0
[2]
https://lore.kernel.org/r/58b661d0-0ebb-4b45-a10d-c5927fb791cd@paulmck-laptop
Signed-off-by: Junli Liu <liuju...@lixiang.com>
This version seems applicable to me:
Reviewed-by: Gao Xiang <hsiang...@linux.alibaba.com>
Thanks,
Gao Xiang
