On 02/08/2016 12:58 PM, Vladimir Davydov wrote:
On Mon, Feb 08, 2016 at 12:31:47PM +0300, Dmitry Safonov wrote:
With enabled slub_debug alloc_calls_show will try to track location and
user of slab object on each online node, kmem_cache_node structure and
cpu_cache/cpu_slub shouldn't be freed till there is the last reference
to sysfs file.
Fixes the following panic:
[43963.463055] BUG: unable to handle kernel
[43963.463090] NULL pointer dereference at 0000000000000020
[43963.463146] IP: [<ffffffff811c6959>] list_locations+0x169/0x4e0
[43963.463185] PGD 257304067 PUD 438456067 PMD 0
[43963.463220] Oops: 0000 [#1] SMP
[43963.463850] CPU: 3 PID: 973074 Comm: cat ve: 0 Not tainted 3.10.0-229.7.2.ovz.9.30-00007-japdoll-dirty #2 9.30
[43963.463913] Hardware name: DEPO Computers To Be Filled By O.E.M./H67DE3, BIOS L1.60c 07/14/2011
[43963.463976] task: ffff88042a5dc5b0 ti: ffff88037f8d8000 task.ti: ffff88037f8d8000
[43963.464036] RIP: 0010:[<ffffffff811c6959>] [<ffffffff811c6959>] list_locations+0x169/0x4e0
[43963.464725] Call Trace:
[43963.464756] [<ffffffff811c6d1d>] alloc_calls_show+0x1d/0x30
[43963.464793] [<ffffffff811c15ab>] slab_attr_show+0x1b/0x30
[43963.464829] [<ffffffff8125d27a>] sysfs_read_file+0x9a/0x1a0
[43963.464865] [<ffffffff811e3c6c>] vfs_read+0x9c/0x170
[43963.464900] [<ffffffff811e4798>] SyS_read+0x58/0xb0
[43963.464936] [<ffffffff81612d49>] system_call_fastpath+0x16/0x1b
[43963.464970] Code: 5e 07 12 00 b9 00 04 00 00 3d 00 04 00 00 0f 4f c1 3d 00 04 00 00 89 45 b0 0f 84 c3 00 00 00 48 63 45 b0 49 8b 9c c4 f8 00 00 00 <48> 8b 43 20 48 85 c0 74 b6 48 89 df e8 46 37 44 00 48 8b 53 10
[43963.465119] RIP [<ffffffff811c6959>] list_locations+0x169/0x4e0
[43963.465155] RSP <ffff88037f8dbe28>
[43963.465185] CR2: 0000000000000020
Separated __kmem_cache_release from __kmem_cache_shutdown which now
called on slab_kmem_cache_release (after the last reference to sysfs
file object has dropped).
Reintroduced locking in free_partial as sysfs file might access cache's
partial list after shutdowning - partiall revert of the
commit 69cb8e6b7c2982 ("slub: free slabs without holding locks")
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Suggested-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
The patch looks good to me now, thanks.
Acked-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Thank you for helping me with that patch.
Will resend v9 with your ack and nits.
Two minor nits below:
...
/*
* Attempt to free all partial slabs on a node.
- * This is called from kmem_cache_close(). We must be the last thread
- * using the cache and therefore we do not need to lock anymore.
+ * This is called from __kmem_cache_shutdown(). We must take list_lock
+ * because sysfs file might still access partial list after the shutdowning.
*/
static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n)
{
+ unsigned long flags;
struct page *page, *h;
+ spin_lock_irqsave(&n->list_lock, flags);
Nit: this function is never called with irqs disabled, so
spin_lock_irq() would be enough. We could add BUG_ON(irqs_disabled())
just to be sure.
list_for_each_entry_safe(page, h, &n->partial, lru) {
if (!page->inuse) {
__remove_partial(n, page);
Nit: __remove_partial() (with leading underscores) was introduced solely
to avoid lockdep warning here (see 1e4dd9461fabf). Since we now take
list_lock, we can use remove_partial() (w/o underscores) and hence zap
__remove_partial().
Thanks,
Vladimir
discard_slab(s, page);
} else {
list_slab_objects(s, page,
- "Objects remaining in %s on kmem_cache_close()");
+ "Objects remaining in %s on __kmem_cache_shutdown()");
}
}
+ spin_unlock_irqrestore(&n->list_lock, flags);
}
--
Regards,
Dmitry Safonov
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