Kernel WARNING splat in 3.14-rc1

On my freshly built 3.14-rc1 kernel, I get the following new warning splat from slub:

[   69.008845] ------------[ cut here ]------------
[   69.008861] WARNING: CPU: 0 PID: 1578 at mm/slub.c:1007 deactivate_slab+0x4bb/0x520()
[   69.008863] Modules linked in: rfcomm nfs fscache af_packet lockd sunrpc bnep rtl8723be arc4 rtl8723_common b43 rtl_pci rtlwifi mac80211 cfg80211 btusb bl
uetooth powernow_k8 kvm_amd kvm snd_hda_intel snd_hda_codec bcma snd_hwdep r852 sdhci_pci sdhci snd_pcm sr_mod snd_seq ssb cdrom forcedeth sm_common pcspkr s
nd_timer serio_raw snd_seq_device snd nand mtd mmc_core rfkill ata_generic pata_amd nand_ids nand_bch bch nand_ecc 6lowpan_iphc soundcore btcoexist r592 ac v
ideo memstick button battery sg dm_mod autofs4 thermal processor thermal_sys hwmon
[   69.008934] CPU: 0 PID: 1578 Comm: akonadi_newmail Not tainted 3.14.0-rc1-wl+ #60
[   69.008936] Hardware name: Hewlett-Packard HP Pavilion dv2700 Notebook PC/30D6, BIOS F.27 11/27/2008
[   69.008939]  0000000000000009 ffff880085ab1cd0 ffffffff815ee4a0 0000000000000000
[   69.008945]  ffff880085ab1d08 ffffffff8104e768 ffffea0001ee69c0 ffff8800bb401800
[   69.008950]  0000000000000000 ffff8800bb400c80 0000000000000002 ffff880085ab1d18
[   69.008956] Call Trace:
[   69.008965]  [<ffffffff815ee4a0>] dump_stack+0x4d/0x6f
[   69.008971]  [<ffffffff8104e768>] warn_slowpath_common+0x78/0xa0
[   69.008976]  [<ffffffff8104e845>] warn_slowpath_null+0x15/0x20
[   69.008980]  [<ffffffff8118581b>] deactivate_slab+0x4bb/0x520
[   69.008985]  [<ffffffff81183429>] ? new_slab+0x1f9/0x300
[   69.008989]  [<ffffffff815ebe57>] __slab_alloc+0x34d/0x4f5
[   69.008994]  [<ffffffff81185a6b>] ? kmem_cache_alloc+0x18b/0x1c0
[   69.008999]  [<ffffffff810770d1>] ? prepare_creds+0x21/0x1a0
[   69.009003]  [<ffffffff810770d1>] ? prepare_creds+0x21/0x1a0
[   69.009007]  [<ffffffff81185a6b>] kmem_cache_alloc+0x18b/0x1c0
[   69.009011]  [<ffffffff810770d1>] prepare_creds+0x21/0x1a0
[   69.009016]  [<ffffffff8119f955>] SyS_access+0x35/0x1f0
[   69.009019]  [<ffffffff815fe8a2>] system_call_fastpath+0x16/0x1b
[   69.009019] ---[ end trace c63f75644bfb030a ]---

There is a similar warning for my other CPU as well. The warning comes from "lockdep_assert_held(&n->list_lock);".

If needed, I can bisect this issue.

Larry

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Commit c65c1877bd68 ("slub: use lockdep_assert_held") incorrectly required that add_full() and remove_full() hold n->list_lock. The lock is only taken when kmem_cache_debug(s), since that's the only time it actually does anything.

Require that the lock only be taken under such a condition.

---
 mm/slub.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

@@ -1004,21 +1004,19 @@ static inline void slab_free_hook(struct kmem_cache *s, void *x)
 static void add_full(struct kmem_cache *s,
 	struct kmem_cache_node *n, struct page *page)
 {
-	lockdep_assert_held(&n->list_lock);
-
 	if (!(s->flags & SLAB_STORE_USER))
 		return;
 
+	lockdep_assert_held(&n->list_lock);
 	list_add(&page->lru, &n->full);
 }
 
 static void remove_full(struct kmem_cache *s, struct kmem_cache_node *n, struct page *page)
 {
-	lockdep_assert_held(&n->list_lock);
-
 	if (!(s->flags & SLAB_STORE_USER))
 		return;
 
+	lockdep_assert_held(&n->list_lock);
 	list_del(&page->lru);
 }
 

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You may add a "Tested-by: Larry Finger <[email protected]>". The patch cleans up the splat on my system. Thanks for the quick response.

Larry

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Please feel free to add mine as well:

And also feel free to ignore my patch as well. ;-)

Thanx, Paul

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Commit c65c1877bd68 ("slub: use lockdep_assert_held") incorrectly required that add_full() and remove_full() hold n->list_lock. The lock is only taken when kmem_cache_debug(s), since that's the only time it actually does anything.

Require that the lock only be taken under such a condition.

---
 mm/slub.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

@@ -1004,21 +1004,19 @@ static inline void slab_free_hook(struct kmem_cache *s, void *x)
 static void add_full(struct kmem_cache *s,
 	struct kmem_cache_node *n, struct page *page)
 {
-	lockdep_assert_held(&n->list_lock);
-
 	if (!(s->flags & SLAB_STORE_USER))
 		return;
 
+	lockdep_assert_held(&n->list_lock);
 	list_add(&page->lru, &n->full);
 }
 
 static void remove_full(struct kmem_cache *s, struct kmem_cache_node *n, struct page *page)
 {
-	lockdep_assert_held(&n->list_lock);
-
 	if (!(s->flags & SLAB_STORE_USER))
 		return;
 
+	lockdep_assert_held(&n->list_lock);
 	list_del(&page->lru);
 }
 

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