linux-kernel - [PATCH] ovl: disable IOCB_DIO_CALLER

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Date:   Mon, 25 Sep 2023 00:21:35 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Amir Goldstein <amir73il@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-unionfs@...r.kernel.org
Cc:     Zorro Lang <zlang@...hat.com>
Subject: [PATCH] ovl: disable IOCB_DIO_CALLER_COMP

overlayfs copies the kiocb flags when it sets up a new kiocb to handle
a write, but it doesn't properly support dealing with the deferred
caller completions of the kiocb. This means it doesn't get the final
write completion value, and hence will complete the write with '0' as
the result.

We could support the caller completions in overlayfs, but for now let's
just disable them in the generated write kiocb.

Reported-by: Zorro Lang <zlang@...hat.com>
Link: https://lore.kernel.org/io-uring/20230924142754.ejwsjen5pvyc32l4@dell-per750-06-vm-08.rhts.eng.pek2.redhat.com/
Fixes: 8c052fb3002e ("iomap: support IOCB_DIO_CALLER_COMP")
Signed-off-by: Jens Axboe <axboe@...nel.dk>

---

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 4193633c4c7a..693971d20280 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -391,6 +391,12 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 	if (!ovl_should_sync(OVL_FS(inode->i_sb)))
 		ifl &= ~(IOCB_DSYNC | IOCB_SYNC);
 
+	/*
+	 * Overlayfs doesn't support deferred completions, don't copy
+	 * this property in case it is set by the issuer.
+	 */
+	ifl &= ~IOCB_DIO_CALLER_COMP;
+
 	old_cred = ovl_override_creds(file_inode(file)->i_sb);
 	if (is_sync_kiocb(iocb)) {
 		file_start_write(real.file);

-- 
Jens Axboe