Re: [Cerowrt-devel] TFO crashes cerowrt 3.7.1-1

[Ketan Kulkarni <ketkulka@gmail.com>]

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Thanks Eric and Yuchung for taking care of the patch. I will test few more
TFO cases as well once this patch is built in cero.

Thanks,
Ketan

On Jan 14, 2013 9:37 AM, "Eric Dumazet" <edumazet@google.com> wrote:
>
> Quite frankly I would just remove the BUG_ON()
>
> diff --git a/net/core/request_sock.c b/net/core/request_sock.c
> index c31d9e8..4425148 100644
> --- a/net/core/request_sock.c
> +++ b/net/core/request_sock.c
> @@ -186,8 +186,6 @@ void reqsk_fastopen_remove(struct sock *sk, struct
request_sock *req,
>         struct fastopen_queue *fastopenq =
>             inet_csk(lsk)->icsk_accept_queue.fastopenq;
>
> -       BUG_ON(!spin_is_locked(&sk->sk_lock.slock) &&
!sock_owned_by_user(sk));
> -
>         tcp_sk(sk)->fastopen_rsk = NULL;
>         spin_lock_bh(&fastopenq->lock);
>         fastopenq->qlen--;
>
>
>
> On Sun, Jan 13, 2013 at 7:05 PM, Eric Dumazet <edumazet@google.com> wrote:
>>
>> Oh well yes, this doesnt quite work on !SMP.
>>
>> 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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