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locks: make locks_mandatory_area check for file-private locks

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Allow locks_mandatory_area() to handle file-private locks correctly.
If there is a file-private lock set on an open file and we're doing I/O
via the same, then that should not cause anything to block.

Handle this by first doing a non-blocking FL_ACCESS check for a
file-private lock, and then fall back to checking for a classic POSIX
lock (and possibly blocking).

Note that this approach is subject to the same races that have always
plagued mandatory locking on Linux.

Reported-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
This commit is contained in:
Jeff Layton 2014-03-10 09:54:19 -04:00
parent d7a06983a0
commit 29723adee1
1 changed files with 13 additions and 2 deletions
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15
fs/locks.c
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@ -1199,19 +1199,30 @@ int locks_mandatory_area(int read_write, struct inode *inode,
{
struct file_lock fl;
int error;
bool sleep = false;
locks_init_lock(&fl);
fl.fl_owner = current->files;
fl.fl_pid = current->tgid;
fl.fl_file = filp;
fl.fl_flags = FL_POSIX | FL_ACCESS;
if (filp && !(filp->f_flags & O_NONBLOCK))
fl.fl_flags |= FL_SLEEP;
sleep = true;
fl.fl_type = (read_write == FLOCK_VERIFY_WRITE) ? F_WRLCK : F_RDLCK;
fl.fl_start = offset;
fl.fl_end = offset + count - 1;
for (;;) {
if (filp) {
fl.fl_owner = (fl_owner_t)filp;
fl.fl_flags &= ~FL_SLEEP;
error = __posix_lock_file(inode, &fl, NULL);
if (!error)
break;
}
if (sleep)
fl.fl_flags |= FL_SLEEP;
fl.fl_owner = current->files;
error = __posix_lock_file(inode, &fl, NULL);
if (error != FILE_LOCK_DEFERRED)
break;