From: Eric Dumazet <edumazet@google.com>
To: Jerry Chu <hkchu@google.com>
Cc: cerowrt-devel <cerowrt-devel@lists.bufferbloat.net>,
Yuchung Cheng <ycheng@google.com>
Subject: Re: [Cerowrt-devel] TFO crashes cerowrt 3.7.1-1
Date: Mon, 14 Jan 2013 08:32:26 -0800 [thread overview]
Message-ID: <CANn89iJ4OAO-sNaWQZm2rpi4xTa9xRBoAMxaZ=LV7=Py4Jgibw@mail.gmail.com> (raw)
In-Reply-To: <CAPshTCgAsBkdQrVFFBPTUqgkKoWJzQs3DVUie4cKTpuX9hhuDw@mail.gmail.com>
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Some paths want to check a spinlock is held, others want to check if its
not held, it depends on the context.
So returning 1 on UP would break a bunch of code as well.
On Mon, Jan 14, 2013 at 12:18 AM, Jerry Chu <hkchu@google.com> wrote:
>
>
> On Sun, Jan 13, 2013 at 7:05 PM, Eric Dumazet <edumazet@google.com> wrote:
>
>> Oh well yes, this doesnt quite work on !SMP.
>>
>
> Strange - how would one assert a spin lock is held, and obviously only for
> SMP? (I almost think arch_spin_is_locked(lock) should be ((void)(lock),
> 1) for UP for the purpose of assertion...)
>
> Also it looks like there are bunch of other places spin_is_locked()
> assertion is made in the source tree. (Perhaps they are only configured for
> MP?)
>
> Thanks,
>
> Jerry
>
>
>> And this kind of bug is frequent....
>>
>> See following example :
>>
>> commit b9980cdcf2524c5fe15d8cbae9c97b3ed6385563
>> Author: Hugh Dickins <hughd@google.com>
>> Date: Wed Feb 8 17:13:40 2012 -0800
>>
>> mm: fix UP THP spin_is_locked BUGs
>>
>> Fix CONFIG_TRANSPARENT_HUGEPAGE=y CONFIG_SMP=n CONFIG_DEBUG_VM=y
>> CONFIG_DEBUG_SPINLOCK=n kernel: spin_is_locked() is then always false,
>> and so triggers some BUGs in Transparent HugePage codepaths.
>>
>> asm-generic/bug.h mentions this problem, and provides a
>> WARN_ON_SMP(x);
>> but being too lazy to add VM_BUG_ON_SMP, BUG_ON_SMP, WARN_ON_SMP_ONCE,
>> VM_WARN_ON_SMP_ONCE, just test NR_CPUS != 1 in the existing
>> VM_BUG_ONs.
>>
>> Signed-off-by: Hugh Dickins <hughd@google.com>
>> Cc: Andrea Arcangeli <aarcange@redhat.com>
>> Cc: <stable@vger.kernel.org>
>> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index b3ffc21..91d3efb 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -2083,7 +2083,7 @@ static void collect_mm_slot(struct mm_slot *mm_slot)
>> {
>> struct mm_struct *mm = mm_slot->mm;
>>
>> - VM_BUG_ON(!spin_is_locked(&khugepaged_mm_lock));
>> + VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
>>
>>
>>
>>
>> On Sun, Jan 13, 2013 at 1:39 PM, Felix Fietkau <nbd@openwrt.org> wrote:
>>
>>> On 2013-01-13 7:03 PM, Eric Dumazet wrote:
>>> > I suspect a bug in the spin_is_locked() implementation on your arch, as
>>> > he socket lock should be held at this point.
>>> I don't think this is an arch implementation bug, this probably happens
>>> on all !SMP systems. See this bit from include/linux/spinlock_up.h:
>>>
>>> #define arch_spin_is_locked(lock) ((void)(lock), 0)
>>>
>>> - Felix
>>>
>>>
>>
>
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next prev parent reply other threads:[~2013-01-14 16:32 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-04 17:04 Dave Taht
2013-01-04 17:27 ` Eric Dumazet
2013-01-04 17:33 ` Dave Taht
2013-01-04 20:42 ` Maciej Soltysiak
2013-01-04 20:43 ` Maciej Soltysiak
2013-01-04 20:57 ` Jerry Chu
2013-01-04 21:21 ` Dave Taht
2013-01-04 21:36 ` Jerry Chu
2013-01-04 21:44 ` Dave Taht
2013-01-04 21:01 ` dpreed
2013-01-04 22:49 ` Robert Bradley
2013-01-04 21:11 ` Dave Taht
2013-01-04 21:19 ` Jerry Chu
2013-01-05 1:59 ` Ketan Kulkarni
2013-01-05 2:20 ` Yuchung Cheng
2013-01-05 3:02 ` Ketan Kulkarni
2013-01-05 3:16 ` Eric Dumazet
2013-01-05 3:35 ` Dave Taht
2013-01-05 4:05 ` Dave Taht
2013-01-05 19:13 ` Ketan Kulkarni
2013-01-13 17:01 ` Ketan Kulkarni
2013-01-13 18:03 ` Eric Dumazet
2013-01-13 21:39 ` Felix Fietkau
2013-01-14 0:38 ` Yuchung Cheng
2013-01-14 3:05 ` Eric Dumazet
2013-01-14 4:07 ` Eric Dumazet
2013-01-14 4:43 ` Ketan Kulkarni
2013-01-14 6:14 ` Dave Taht
2013-01-14 19:50 ` Dave Taht
2013-01-14 8:18 ` Jerry Chu
2013-01-14 16:32 ` Eric Dumazet [this message]
2013-01-04 22:25 ` Robert Bradley
2013-01-14 6:11 ` Dave Taht
2013-01-14 16:37 ` Ketan Kulkarni
2013-01-16 22:19 ` Maciej Soltysiak
2013-01-17 0:58 ` Dave Taht
2013-01-17 3:44 ` Dave Taht
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