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SubjectRe: [PATCH] Memory shortage can result in inconsistent flocks state
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On Thu, Sep 13, 2007 at 03:27:08PM -0400, Chuck Ebbert wrote:
> On 09/11/2007 08:38 AM, Pavel Emelyanov wrote:
> > diff --git a/fs/locks.c b/fs/locks.c
> > index 0db1a14..f59d066 100644
> > --- a/fs/locks.c
> > +++ b/fs/locks.c
> > @@ -732,6 +732,14 @@ static int flock_lock_file(struct file *
> > lock_kernel();
> > if (request->fl_flags & FL_ACCESS)
> > goto find_conflict;
> > +
> > + if (request->fl_type != F_UNLCK) {
> > + error = -ENOMEM;
> > + new_fl = locks_alloc_lock();
> > + if (new_fl == NULL)
> > + goto out;
> > + }
> > +
> > for_each_lock(inode, before) {
> > struct file_lock *fl = *before;
> > if (IS_POSIX(fl))
> > @@ -753,10 +761,6 @@ static int flock_lock_file(struct file *
> > goto out;
> > }
> >
> > - error = -ENOMEM;
> > - new_fl = locks_alloc_lock();
> > - if (new_fl == NULL)
> > - goto out;
> > /*
> > * If a higher-priority process was blocked on the old file lock,
> > * give it the opportunity to lock the file.
>
> Doesn't that create a leak in some cases?
>
> > for_each_lock(inode, before) {
> > struct file_lock *fl = *before;
> > if (IS_POSIX(fl))
> > break;
> > if (IS_LEASE(fl))
> > continue;
> > if (filp != fl->fl_file)
> > continue;
> > if (request->fl_type == fl->fl_type)
> > goto out; <<<<<<<<<<<<<<<< LEAK?

You mean, a leak of the memory allocated for new_fl? That's freed at
the exit labeled with "out". It's the only exit:

out:
unlock_kernel();
if (new_fl)
locks_free_lock(new_fl);
return error;
And new_fl is initially NULL, assigned only once by the allocation, then
assigned to NULL only at the very end when we know we've succeeded.

Am I missing something else?

--b.

> > found = 1;
> > locks_delete_lock(before);
> > break;
> > }
-
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