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From: Gabriel Krisman Bertazi <krisman@collabora.com>
To: viro@zeniv.linux.org.uk
Cc: linux-fsdevel@vger.kernel.org, jack@suse.cz, khazhy@google.com,
	Gabriel Krisman Bertazi <krisman@collabora.com>,
	kernel@collabora.com, Jamie Liu <jamieliu@google.com>
Subject: [PATCH v3 3/3] direct-io: defer alignment check until after the EOF check
Date: Sat,  5 Sep 2020 01:20:23 -0400	[thread overview]
Message-ID: <20200905052023.3719585-4-krisman@collabora.com> (raw)
In-Reply-To: <20200905052023.3719585-1-krisman@collabora.com>

Prior to commit 9fe55eea7e4b ("Fix race when checking i_size on direct
i/o read"), an unaligned direct read past end of file would trigger EOF,
since generic_file_aio_read detected this read-at-EOF condition and
skipped the direct IO read entirely, returning 0. After that change, the
read now reaches dio_generic, which detects the misalignment and returns
EINVAL.

This consolidates the generic direct-io to follow the same behavior of
filesystems.  Apparently, this fix will only affect ocfs2 since other
filesystems do this verification before calling do_blockdev_direct_IO,
with the exception of f2fs, which has the same bug, but is fixed in the
next patch.

it can be verified by a read loop on a file that does a partial read
before EOF (On file that doesn't end at an aligned address).  The
following code fails on an unaligned file on filesystems without
prior validation without this patch, but not on btrfs, ext4, and xfs.

  while (done < total) {
    ssize_t delta = pread(fd, buf + done, total - done, off + done);
    if (!delta)
      break;
    ...
  }

Fix this regression by moving the misalignment check to after the EOF
check added by commit 74cedf9b6c60 ("direct-io: Fix negative return from
dio read beyond eof").

Based on a patch by Jamie Liu.

Reported-by: Jamie Liu <jamieliu@google.com>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
---
 fs/direct-io.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index c17efe58f1c9..82838cca934b 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1165,14 +1165,6 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 	 * the early prefetch in the caller enough time.
 	 */
 
-	if (align & blocksize_mask) {
-		if (bdev)
-			blkbits = blksize_bits(bdev_logical_block_size(bdev));
-		blocksize_mask = (1 << blkbits) - 1;
-		if (align & blocksize_mask)
-			return -EINVAL;
-	}
-
 	/* watch out for a 0 len io from a tricksy fs */
 	if (iov_iter_rw(iter) == READ && !count)
 		return 0;
@@ -1200,6 +1192,14 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 		goto fail_dio;
 	}
 
+	if (align & blocksize_mask) {
+		if (bdev)
+			blkbits = blksize_bits(bdev_logical_block_size(bdev));
+		blocksize_mask = (1 << blkbits) - 1;
+		if (align & blocksize_mask)
+			goto fail_dio;
+	}
+
 	if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ) {
 		struct address_space *mapping = iocb->ki_filp->f_mapping;
 
-- 
2.28.0


  parent reply	other threads:[~2020-09-05  5:20 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-05  5:20 [PATCH v3 0/3] Unaligned DIO read error path fix and clean ups Gabriel Krisman Bertazi
2020-09-05  5:20 ` [PATCH v3 1/3] direct-io: clean up error paths of do_blockdev_direct_IO Gabriel Krisman Bertazi
2020-09-07  9:32   ` Jan Kara
2020-09-05  5:20 ` [PATCH v3 2/3] direct-io: don't force writeback for reads beyond EOF Gabriel Krisman Bertazi
2020-09-05  5:20 ` Gabriel Krisman Bertazi [this message]
2020-09-07  9:36   ` [PATCH v3 3/3] direct-io: defer alignment check until after the EOF check Jan Kara

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