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SubjectRe: [PATCH] fix race in mark_mounts_for_expiry()
Date
Miklos Szeredi <miklos@szeredi.hu> wrote:

> > How about using cmpxchg?
>
> How? If the count is nonzero, an incremented count must be stored.
> You can't do that atomically with cmpxchg.

Yes you can. cmpxchg() is atomic. Several archs implement atomic_inc() and co
with cmpxchg() or similar.

Something like:

static inline struct namespace *grab_namespace(struct namespace *n)
{
int old = atomic_read(&n->count);

while (old > 0) {
/* attempt to increment the counter */
old = cmpxchg(&n->count, old, old + 1);
}

return old > 0 ? n : NULL;
}

David
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