Re: [PATCH] ext4: wait for tail page commit in ext4_truncate_failed_write()

[sashiko-bot@kernel.org]

> When a buffered write fails partially (e.g., due to a user page fault)
> on an ext4 filesystem mounted in data=journal mode with blocksize <
> PAGE_SIZE, ext4_journalled_write_end() invokes ext4_truncate_failed_write()
> to discard newly allocated blocks beyond inode->i_size.
> 
> If the updated inode->i_size straddles a folio whose buffers are currently
> being committed to the journal, truncate_inode_pages() attempts to
> partially invalidate that folio via ext4_journalled_invalidate_folio().
> Because JBD2 cannot unmap buffers belonging to a committing transaction
> on a partial folio, journal_unmap_buffer() returns -EBUSY, triggering
> the WARN_ON() in ext4_journalled_invalidate_folio().
> 
> Unlike the standard truncate path in ext4_truncate_down(),
> ext4_truncate_failed_write() does not wait for the committing
> transaction on the tail page to finish before truncating the page cache.
> Export ext4_wait_for_tail_page_commit() and call it in
> ext4_truncate_failed_write() when data=journal is enabled before
> acquiring filemap_invalidate_lock() and calling truncate_inode_pages().
> 
> Fixes: 53e872681fed ("ext4: fix deadlock in journal_unmap_buffer()")
> Reported-by: syzbot+f111db4cb2acd44eb2f4@syzkaller.appspotmail.com
> Closes: https://syzbot.org/bug?extid=f111db4cb2acd44eb2f4
> Signed-off-by: Chandradhar Kumar <chandradhar.2003@gmail.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261112124835.114888-1-chandradhar.2003@gmail.com?part=1