Re: file locking fix for 3.2

From: J. Bruce Fields
Date: Sun Dec 25 2011 - 13:20:32 EST

On Sun, Dec 25, 2011 at 12:05:42AM +0000, Al Viro wrote:
> On Sat, Dec 24, 2011 at 06:50:35PM -0500, J. Bruce Fields wrote:
> > Then you're returning -ENOMEM in a case when we really didn't need to do
> > an allocation, but is that really a problem? It's a rare case, and
> > opens can already fail with -ENOMEM for other reasons, and I'd rather
> > not have the extra hair.
> I'm certainly OK with that variant; if the folks maintaining fs/locks.c

I've been more-or-less assuming that's me, not that I've been doing much
real maintenance to speak of.

> are happy with it, I'd suggest going for it. Note that you don't need
> to touch locks_conflict() call at all if you bail out early on allocation
> failure and it's definitely simpler and cleaner that way.


With no more -rc, and no chance to test anything myself till I'm back
from the holidays, my preference would be for Linus to merge the
already-posted one-liner. Then I can queue up the below for 3.3.


commit 72acf27f6c20573d555d6b4450a7a9d41c4c9d5a
Author: J. Bruce Fields <bfields@xxxxxxxxxx>
Date: Sun Dec 25 10:51:37 2011 -0700

locks: simplify allocation in break_lease

The code bends over backwards to avoid returning -ENOMEM in cases where
the allocation wasn't really necessary.

But there's nothing really *wrong* with returning -ENOMEM in those
cases: break_lease callers can already return -ENOMEM for other reasons.
So let's not take so much trouble over a rare case, and keep the code

Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>

diff --git a/fs/locks.c b/fs/locks.c
index 96a487a..0bd1745 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1205,6 +1205,8 @@ int __break_lease(struct inode *inode, unsigned int mode)
int want_write = (mode & O_ACCMODE) != O_RDONLY;

new_fl = lease_alloc(NULL, want_write ? F_WRLCK : F_RDLCK);
+ if (IS_ERR(new_fl))
+ return PTR_ERR(new_fl);


@@ -1214,19 +1216,13 @@ int __break_lease(struct inode *inode, unsigned int mode)
if ((flock == NULL) || !IS_LEASE(flock))
goto out;

- if (flock->fl_type == F_RDLCK && !want_write)
- goto out; /* no conflict */
+ if (!locks_conflict(flock, new_fl))
+ goto out;

for (fl = flock; fl && IS_LEASE(fl); fl = fl->fl_next)
if (fl->fl_owner == current->files)
i_have_this_lease = 1;

- if (IS_ERR(new_fl) && !i_have_this_lease
- && ((mode & O_NONBLOCK) == 0)) {
- error = PTR_ERR(new_fl);
- goto out;
- }
break_time = 0;
if (lease_break_time > 0) {
break_time = jiffies + lease_break_time * HZ;
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