Re: kernel: smp: WARNING at kernel/smp.c:673

[Andrew Morton]

On Mon, 4 Aug 2014 15:48:23 +0900 Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote:

> > While fuzzing with trinity inside a KVM tools guest running the latest -next
> > kernel, I've stumbled on the following spew:
> > 
> > 
> > [ 1226.701012] WARNING: CPU: 6 PID: 8624 at kernel/smp.c:673 on_each_cpu_cond+0x27f/0x2f0()
> > [ 1226.703128] Modules linked in:
> > [ 1226.703955] CPU: 6 PID: 8624 Comm: trinity-c26 Tainted: G        W      3.16.0-rc7-next-20140801-sasha-00047-gd6ce559 #991
> > [ 1226.706792]  ffff881b2e8a3000 0000000023830039 0000000000000000 ffff881b2e8a3000
> > [ 1226.708179]  ffff881ada5b3978 ffffffffa1ee96b4 0000000000000000 ffff881ada5b39b8
> > [ 1226.709610]  ffffffff9d1ce5ba ffffffff9d2c0ddf 000000000000001b ffff8807d7608000
> > [ 1226.710966] Call Trace:
> > [ 1226.711417] dump_stack (lib/dump_stack.c:52)
> > [ 1226.712311] warn_slowpath_common (kernel/panic.c:432)
> > [ 1226.715425] warn_slowpath_null (kernel/panic.c:466)
> > [ 1226.716436] on_each_cpu_cond (kernel/smp.c:673 (discriminator 3))
> > [ 1226.720821] __kmem_cache_shrink (mm/slub.c:3420)
> > [ 1226.722711] slab_memory_callback (mm/slub.c:3464 mm/slub.c:3556)
> > [ 1226.723925] notifier_call_chain (kernel/notifier.c:93)
> > [ 1226.725244] __blocking_notifier_call_chain (kernel/notifier.c:319)
> > [ 1226.726310] blocking_notifier_call_chain (kernel/notifier.c:329)
> > [ 1226.727263] memory_notify (drivers/base/memory.c:177)
> > [ 1226.728210] __offline_pages.constprop.23 (include/linux/notifier.h:179 mm/memory_hotplug.c:1682)
> > [ 1226.731896] offline_pages (mm/memory_hotplug.c:1787)
> > [ 1226.733095] memory_subsys_offline (drivers/base/memory.c:267 drivers/base/memory.c:304)
> > [ 1226.735208] device_offline (drivers/base/core.c:1428)
> > [ 1226.736966] online_store (drivers/base/core.c:451 (discriminator 2))
> > [ 1226.737720] dev_attr_store (drivers/base/core.c:138)
> > [ 1226.739986] sysfs_kf_write (fs/sysfs/file.c:116)
> > [ 1226.742105] kernfs_fop_write (fs/kernfs/file.c:308)
> > [ 1226.743058] do_loop_readv_writev (fs/read_write.c:708)
> > [ 1226.745095] do_readv_writev (fs/read_write.c:840)
> > [ 1226.752769] vfs_writev (fs/read_write.c:879)
> > [ 1226.753755] SyS_writev (fs/read_write.c:911 fs/read_write.c:903)
> > [ 1226.754660] tracesys (arch/x86/kernel/entry_64.S:541)
> > 
> > No time to dig too much into this today, will work on it tomorrow.
> 
> I think that that WARN_ON_ONCE() in kernel/smp.c:673 is wrong.
> smp_call_function_single() returns 0 if success so it should be
> WARN_ON_ONCE(ret) rather than WARN_ON_ONCE(!ret).

Surely true.


From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: kernel/smp.c:on_each_cpu_cond(): fix warning in fallback path

The rarely-executed memry-allocation-failed callback path generates a
WARN_ON_ONCE() when smp_call_function_single() succeeds.  Presumably it's
supposed to warn on failures.

Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxxx>
Cc: Gilad Ben-Yossef <gilad@xxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Tejun Heo <htejun@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 kernel/smp.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -puN kernel/smp.c~a kernel/smp.c
--- a/kernel/smp.c~a
+++ a/kernel/smp.c
@@ -661,7 +661,7 @@ void on_each_cpu_cond(bool (*cond_func)(
 			if (cond_func(cpu, info)) {
 				ret = smp_call_function_single(cpu, func,
 								info, wait);
-				WARN_ON_ONCE(!ret);
+				WARN_ON_ONCE(ret);
 			}
 		preempt_enable();
 	}
_

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