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    Subject[PATCH AUTOSEL 4.14 16/58] ext4: update direct I/O read lock pattern for IOCB_NOWAIT
    Date
    From: Matthew Bobrowski <mbobrowski@mbobrowski.org>

    [ Upstream commit 548feebec7e93e58b647dba70b3303dcb569c914 ]

    This patch updates the lock pattern in ext4_direct_IO_read() to not
    block on inode lock in cases of IOCB_NOWAIT direct I/O reads. The
    locking condition implemented here is similar to that of 942491c9e6d6
    ("xfs: fix AIM7 regression").

    Fixes: 16c54688592c ("ext4: Allow parallel DIO reads")
    Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
    Reviewed-by: Jan Kara <jack@suse.cz>
    Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
    Link: https://lore.kernel.org/r/c5d5e759f91747359fbd2c6f9a36240cf75ad79f.1572949325.git.mbobrowski@mbobrowski.org
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/ext4/inode.c | 8 +++++++-
    1 file changed, 7 insertions(+), 1 deletion(-)

    diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
    index b3d5fd84b4856..f746abfd96977 100644
    --- a/fs/ext4/inode.c
    +++ b/fs/ext4/inode.c
    @@ -3787,7 +3787,13 @@ static ssize_t ext4_direct_IO_read(struct kiocb *iocb, struct iov_iter *iter)
    * writes & truncates and since we take care of writing back page cache,
    * we are protected against page writeback as well.
    */
    - inode_lock_shared(inode);
    + if (iocb->ki_flags & IOCB_NOWAIT) {
    + if (!inode_trylock_shared(inode))
    + return -EAGAIN;
    + } else {
    + inode_lock_shared(inode);
    + }
    +
    ret = filemap_write_and_wait_range(mapping, iocb->ki_pos,
    iocb->ki_pos + count - 1);
    if (ret)
    --
    2.20.1
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