Re: [f2fs-dev] [PATCH v14 13/21] xfs: use read ioend for fsverity data verification

> > > "If we have fsverity and block device integrity attached to this bio,
> > > we need to run both validations from the separate fsverity workqueue
> > > to avoid deadlocking due to fsverity issuing its own reads."
> > > 
> > > (Assuming I understand the fsverity && pi case correctly.)
> > > 
> > > One thing I'm not clear about -- why is it safe to do the fsverity
> > > validation here if PI isn't enabled?  Can't that also issue IO to pull
> > > in merkle tree blocks?
> > 
> > Without PI, fsverity metadata is read without XFS bio completion
> > path, we don't get here for the descriptor/metadata reads
> > (see xfs_get_iomap_read_ops()). So, we won't block the queue, as
> > data ioends won't be mixed with metadata ioends.
> > 
> > With PI, all fsverity reads goes through this path. We could get a
> > case that data ioend is waiting for metadata IO to be completed which
> > in turn is pending for data ioend to be finished (due to batch
> > processing of multiple BIOs in the bio_complete wq).
> > 
> > So, this will issue more IO, but this IO will not get onto this
> > queue (it will go through iomap_bio_submit_read()).
> 
> Ah, ok.  Maybe add to that comment:
> 
> "If we have fsverity enabled but block device integrity is not enabled,
> completion of the fsverity metadata reads does not require a workqueue
> so there is no deadlock potential."
> 
> then?
> 
> (Just echoing you to make sure I understand completely.)
> 

yes,

I've changed it to:

+       /*
+        * If we have fsverity and block device integrity attached to this bio,
+        * we need to run fsverity verification of data folios from a separate
+        * fsverity workqueue. This is necessary to avoid deadlocking due to
+        * fsverity issuing more reads of fsverity metadata which would be
+        * processed by the same worker in the BIO completion workqueue.
+        *
+        * Without device integrity, fsverity metadata IO will not use ioends for
+        * completion.
+        */


-- 
- Andrey



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