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SubjectRe: 2.6.16rc1-git4 slab corruption.
On Wed, Feb 01, 2006 at 09:27:02AM +0200, Pekka Enberg wrote:
> Hi,
>
> On 2/1/06, Dave Jones <davej@redhat.com> wrote:
> > Manfred had a nice 'check all slabs before they're freed' patch, which might
> > be worth resurrecting for some tests. It may be that we're corrupting rarely
> > free'd slabs, making them hard to hit.
>
> Do you know where I can find that patch? I would like to try to sneak
> that past Andrew. It seems silly not to have these useful slab
> debugging patches within mainline.

Here's the last version that I had that was rediffed against
2.6.13 or .14 (I forget which, it's been a while since I used it).

Dave


diff -urNp --exclude-from=/home/davej/.exclude linux-1000/mm/slab.c linux-1010/mm/slab.c
--- linux-1000/mm/slab.c
+++ linux-1010/mm/slab.c
@@ -189,7 +189,7 @@
*/

#define BUFCTL_END (((kmem_bufctl_t)(~0U))-0)
-#define BUFCTL_FREE (((kmem_bufctl_t)(~0U))-1)
+#define BUFCTL_ALLOC (((kmem_bufctl_t)(~0U))-1)
#define SLAB_LIMIT (((kmem_bufctl_t)(~0U))-2)

/* Max number of objs-per-slab for caches which use off-slab slabs.
@@ -355,6 +355,7 @@ struct kmem_cache_s {
#if DEBUG
int dbghead;
int reallen;
+ unsigned long redzonetest;
#endif
};

@@ -370,6 +371,7 @@ struct kmem_cache_s {
*/
#define REAPTIMEOUT_CPUC (2*HZ)
#define REAPTIMEOUT_LIST3 (4*HZ)
+#define REDZONETIMEOUT (300*HZ)

#if STATS
#define STATS_INC_ACTIVE(x) ((x)->num_active++)
@@ -1446,7 +1448,11 @@ next:
}

cachep->lists.next_reap = jiffies + REAPTIMEOUT_LIST3 +
- ((unsigned long)cachep)%REAPTIMEOUT_LIST3;
+ ((unsigned long)cachep/L1_CACHE_BYTES)%REAPTIMEOUT_LIST3;
+#if DEBUG
+ cachep->redzonetest = jiffies + REDZONETIMEOUT +
+ ((unsigned long)cachep/L1_CACHE_BYTES)%REDZONETIMEOUT;
+#endif

/* Need the semaphore to access the chain. */
down(&cache_chain_sem);
@@ -2043,7 +2049,7 @@ retry:
slabp->inuse++;
next = slab_bufctl(slabp)[slabp->free];
#if DEBUG
- slab_bufctl(slabp)[slabp->free] = BUFCTL_FREE;
+ slab_bufctl(slabp)[slabp->free] = BUFCTL_ALLOC;
#endif
slabp->free = next;
}
@@ -2181,7 +2187,7 @@ static void free_block(kmem_cache_t *cac
objnr = (objp - slabp->s_mem) / cachep->objsize;
check_slabp(cachep, slabp);
#if DEBUG
- if (slab_bufctl(slabp)[objnr] != BUFCTL_FREE) {
+ if (slab_bufctl(slabp)[objnr] != BUFCTL_ALLOC) {
printk(KERN_ERR "slab: double free detected in cache '%s', objp %p.\n",
cachep->name, objp);
BUG();
@@ -2409,7 +2415,7 @@ got_slabp:
slabp->inuse++;
next = slab_bufctl(slabp)[slabp->free];
#if DEBUG
- slab_bufctl(slabp)[slabp->free] = BUFCTL_FREE;
+ slab_bufctl(slabp)[slabp->free] = BUFCTL_ALLOC;
#endif
slabp->free = next;
check_slabp(cachep, slabp);
@@ -2615,6 +2621,94 @@ unsigned int kmem_cache_size(kmem_cache_

EXPORT_SYMBOL(kmem_cache_size);

+#if DEBUG
+static void check_slabuse(kmem_cache_t *cachep, struct slab *slabp)
+{
+ int i;
+
+ if (!(cachep->flags & SLAB_RED_ZONE))
+ return; /* no redzone data to check */
+
+#if CONFIG_DEBUG_PAGEALLOC
+ /* Page alloc debugging on for this cache. Mapping & Unmapping happens
+ * without any locking, thus parallel checks are impossible.
+ */
+ if ((cachep->objsize%PAGE_SIZE)==0 && OFF_SLAB(cachep))
+ return;
+#endif
+
+ for (i=0;i<cachep->num;i++) {
+ void *objp = slabp->s_mem + cachep->objsize * i;
+ unsigned long red1, red2;
+
+ red1 = *dbg_redzone1(cachep, objp);
+ red2 = *dbg_redzone2(cachep, objp);
+
+ /* simplest case: marked as inactive */
+ if (red1 == RED_INACTIVE && red2 == RED_INACTIVE)
+ continue;
+
+ /* tricky case: if the bufctl value is BUFCTL_ALLOC, then
+ * the object is either allocated or somewhere in a cpu
+ * cache. The cpu caches are lockless and there might be
+ * a concurrent alloc/free call, thus we must accept random
+ * combinations of RED_ACTIVE and _INACTIVE
+ */
+ if (slab_bufctl(slabp)[i] == BUFCTL_ALLOC &&
+ (red1 == RED_INACTIVE || red1 == RED_ACTIVE) &&
+ (red2 == RED_INACTIVE || red2 == RED_ACTIVE))
+ continue;
+
+ printk(KERN_ERR "slab %s: redzone mismatch in slabp %p, objp %p, bufctl 0x%x\n",
+ cachep->name, slabp, objp, slab_bufctl(slabp)[i]);
+ print_objinfo(cachep, objp, 2);
+ }
+}
+
+/*
+ * Perform a self test on all slabs from a cache
+ */
+static void check_redzone(kmem_cache_t *cachep)
+{
+ struct list_head *q;
+ struct slab *slabp;
+
+ check_spinlock_acquired(cachep);
+
+ list_for_each(q,&cachep->lists.slabs_full) {
+ slabp = list_entry(q, struct slab, list);
+
+ if (slabp->inuse != cachep->num) {
+ printk(KERN_INFO "slab %s: wrong slabp found in full slab chain at %p (%d/%d).\n",
+ cachep->name, slabp, slabp->inuse, cachep->num);
+ }
+ check_slabp(cachep, slabp);
+ check_slabuse(cachep, slabp);
+ }
+ list_for_each(q,&cachep->lists.slabs_partial) {
+ slabp = list_entry(q, struct slab, list);
+
+ if (slabp->inuse == cachep->num || slabp->inuse == 0) {
+ printk(KERN_INFO "slab %s: wrong slab found in partial chain at %p (%d/%d).\n",
+ cachep->name, slabp, slabp->inuse, cachep->num);
+ }
+ check_slabp(cachep, slabp);
+ check_slabuse(cachep, slabp);
+ }
+ list_for_each(q,&cachep->lists.slabs_free) {
+ slabp = list_entry(q, struct slab, list);
+
+ if (slabp->inuse != 0) {
+ printk(KERN_INFO "slab %s: wrong slab found in free chain at %p (%d/%d).\n",
+ cachep->name, slabp, slabp->inuse, cachep->num);
+ }
+ check_slabp(cachep, slabp);
+ check_slabuse(cachep, slabp);
+ }
+}
+
+#endif
+
struct ccupdate_struct {
kmem_cache_t *cachep;
struct array_cache *new[NR_CPUS];
@@ -2798,6 +2892,12 @@ static void cache_reap(void *unused)

drain_array_locked(searchp, ac_data(searchp), 0);

+#if DEBUG
+ if(time_before(searchp->redzonetest, jiffies)) {
+ searchp->redzonetest = jiffies + REDZONETIMEOUT;
+ check_redzone(searchp);
+ }
+#endif
if(time_after(searchp->lists.next_reap, jiffies))
goto next_unlock;


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