Re: [PATCH] fs: jfs: Avoid sleeping function call in softirq

[Purva Yeshi]

On 22/03/25 20:05, Al Viro wrote:
> On Sat, Mar 22, 2025 at 07:51:34PM +0530, Purva Yeshi wrote:
> > Bug detected by Syzbot:
> > BUG: sleeping function called from invalid context in jfs_fsync
> >
> > Fix jfs_fsync() to avoid sleeping in softirq/atomic, preventing crash.
> > Skip execution in softirq/atomic and return -EWOULDBLOCK to prevent issues.
> > Correct generic_file_fsync() call to pass the required arguments properly.
>
> _ANY_ ->fsync() instance may sleep; adding that bandaid in jfs one does
> not fix anything - the realy bug is whatever leads to having that
> *called* in such conditions (e.g. having an unbalanced spin_lock()
> somewhere, etc.)
>
> NAK.

Thanks for the review. Based on your feedback, I have analyzed the call 
path leading to fsync() being invoked in an invalid context. The issue 
arises because generic_write_sync() is being called inside 
dio_complete(), which can be triggered from dio_bio_end_aio().

dio_bio_end_aio() executes as a bio completion handler, which may run in 
a SoftIRQ context. If dio_complete() is called directly (without 
deferring), generic_write_sync() gets executed within SoftIRQ, which is 
problematic since fsync() (invoked later) may sleep.