Re: [PATCH 18/22] xfs: use BIO_COMPLETE_IN_TASK for bounce buffered read I/Os

[Christoph Hellwig <hch@lst.de>]

On Thu, Jul 23, 2026 at 05:58:49PM +0200, Andrey Albershteyn wrote:
> I would probably need something like this for fsverity.
> 
> When using integrity checksums with fsverity together, both file data
> ioends and fsverity metadata ioends get onto the inode queue
> (without checksums there's no metadata ioends). This way worker could
> self-deadlock if data ioend processed first in xfs_end_io(). It will
> call verify_bio to read merkle pages which could be already waiting
> in queue.

Yes.  Same as the situation we have (or had as this is changing
for 7.3) with fsverity and fscrypt.

> I initially considered changing xfs_end_io, for read ioends, to just
> schedule them instead of adding to the queue, but decided just sort
> metadata ioends first in the queue [1] as a bit simpler fix.
> 
> The difference is that work won't be scheduled on the high-priority
> fsverity's workqueue. Not sure how critical this is as with
> checksums all reads would be the same priority.

I'll need to go back to your series, but just sorting isn't going
to fix the problem, as the reading of the verity metadata could
be kicked off from the completion workqueue and you could be blocking
the rescuer thread.  So either verity needs it's own WQ, or we'd need
some way for a currently running I/O completion to exit and get
restarted.

With BIO_COMPLETE_IN_TASK we could probably do that restart thing.
Or add a second set of workers for "metadata".