Re: [PATCH] splice: prevent deadlock when splicing a file to itself

[Deepanshu Kartikey]

On Wed, Apr 01, 2026, Jan Kara wrote:
> Hum, I'm probably missing something but I just
> don't see how the proposed deadlock is supposed
> to happen.

You are correct, I apologize for the incorrect
analysis in the patch description.

After looking more carefully at the code, the
actual deadlock involves sendfile() and a
concurrent fallocate() on the same inode:

1. sendfile() write side calls blkdev_write_iter()
   which acquires inode_lock_shared().

2. Concurrent fallocate() calls blkdev_fallocate()
   which tries inode_lock() (exclusive) and blocks
   waiting for the shared lock to be released.

3. sendfile() read side then calls
   blkdev_read_iter() which tries
   inode_lock_shared() but is blocked because
   rwsem prevents new readers when a writer
   is waiting.

This creates a circular dependency where nobody
can proceed, causing the hung task.

My original patch was fixing the wrong thing.
I will investigate the correct fix.

Thank you for the careful review!