[PATCH 5.4 039/152] ceph: do not execute direct write in parallel if O_APPEND is specified

Greg Kroah-Hartman
2020-03-03T17:53:45Z

From: Xiubo Li <xiubli@redhat.com>

[ Upstream commit 8e4473bb50a1796c9c32b244e5dbc5ee24ead937 ]

In O_APPEND & O_DIRECT mode, the data from different writers will
be possibly overlapping each other since they take the shared lock.

For example, both Writer1 and Writer2 are in O_APPEND and O_DIRECT
mode:

Writer1 Writer2

shared_lock() shared_lock()
getattr(CAP_SIZE) getattr(CAP_SIZE)
iocb->ki_pos = EOF iocb->ki_pos = EOF
write(data1)
write(data2)
shared_unlock() shared_unlock()

The data2 will overlap the data1 from the same file offset, the
old EOF.

Switch to exclusive lock instead when O_APPEND is specified.

Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ceph/file.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 11929d2bb594c..cd09e63d682b7 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -1418,6 +1418,7 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
struct ceph_cap_flush *prealloc_cf;
ssize_t count, written = 0;
int err, want, got;
+ bool direct_lock = false;
loff_t pos;
loff_t limit = max(i_size_read(inode), fsc->max_file_size);

@@ -1428,8 +1429,11 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
if (!prealloc_cf)
return -ENOMEM;

+ if ((iocb->ki_flags & (IOCB_DIRECT | IOCB_APPEND)) == IOCB_DIRECT)
+ direct_lock = true;
+
retry_snap:
- if (iocb->ki_flags & IOCB_DIRECT)
+ if (direct_lock)
ceph_start_io_direct(inode);
else
ceph_start_io_write(inode);
@@ -1519,14 +1523,15 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)

/* we might need to revert back to that point */
data = *from;
- if (iocb->ki_flags & IOCB_DIRECT) {
+ if (iocb->ki_flags & IOCB_DIRECT)
written = ceph_direct_read_write(iocb, &data, snapc,
&prealloc_cf);
- ceph_end_io_direct(inode);
- } else {
+ else
written = ceph_sync_write(iocb, &data, pos, snapc);
+ if (direct_lock)
+ ceph_end_io_direct(inode);
+ else
ceph_end_io_write(inode);
- }
if (written > 0)
iov_iter_advance(from, written);
ceph_put_snap_context(snapc);
@@ -1577,7 +1582,7 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)

goto out_unlocked;
out:
- if (iocb->ki_flags & IOCB_DIRECT)
+ if (direct_lock)
ceph_end_io_direct(inode);
else
ceph_end_io_write(inode);
--
2.20.1