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

[Eric Dumazet <edumazet@google.com>]

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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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