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>
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