Messages in this thread | | | Date | Thu, 1 Oct 2009 13:49:00 -0700 (PDT) | From | David Rientjes <> | Subject | Re: [PATCH 30/31] Fix use of uninitialized variable in cache_grow() |
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On Thu, 1 Oct 2009, Suresh Jayaraman wrote:
> From: Miklos Szeredi <mszeredi@suse.cz> > > This fixes a bug in reserve-slub.patch. > > If cache_grow() was called with objp != NULL then the 'reserve' local > variable wasn't initialized. This resulted in ac->reserve being set to > a rubbish value. Due to this in some circumstances huge amounts of > slab pages were allocated (due to slab_force_alloc() returning true), > which caused atomic page allocation failures and slowdown of the > system. > > Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> > Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de> > --- > mm/slab.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > Index: mmotm/mm/slab.c > =================================================================== > --- mmotm.orig/mm/slab.c > +++ mmotm/mm/slab.c > @@ -2760,7 +2760,7 @@ static int cache_grow(struct kmem_cache > size_t offset; > gfp_t local_flags; > struct kmem_list3 *l3; > - int reserve; > + int reserve = -1; > > /* > * Be lazy and only check for valid flags here, keeping it out of the > @@ -2816,7 +2816,8 @@ static int cache_grow(struct kmem_cache > if (local_flags & __GFP_WAIT) > local_irq_disable(); > check_irq_off(); > - slab_set_reserve(cachep, reserve); > + if (reserve != -1) > + slab_set_reserve(cachep, reserve); > spin_lock(&l3->list_lock); > > /* Make slab active. */
Given the patch description, shouldn't this be a test for objp != NULL instead, then?
If so, it doesn't make sense because reserve will only be initialized when objp == NULL in the call to kmem_getpages() from cache_grow().
The title of the patch suggests this is just dealing with an uninitialized auto variable so the anticipated change would be from "int reserve" to "int uninitialized_var(result)".
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