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Date:   Tue, 19 May 2020 17:43:22 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Neil Horman <nhorman@...driver.com>
Cc:     linux-sctp@...r.kernel.org, Vlad Yasevich <vyasevich@...il.com>,
        "David S. Miller" <davem@...emloft.net>, jere.leppanen@...ia.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH] sctp: Don't add the shutdown timer if its already been
 added

On Tue, May 19, 2020 at 04:04:05PM -0400, Neil Horman wrote:
> This BUG halt was reported a while back, but the patch somehow got
> missed:
> 
> PID: 2879   TASK: c16adaa0  CPU: 1   COMMAND: "sctpn"
>  #0 [f418dd28] crash_kexec at c04a7d8c
>  #1 [f418dd7c] oops_end at c0863e02
>  #2 [f418dd90] do_invalid_op at c040aaca
>  #3 [f418de28] error_code (via invalid_op) at c08631a5
>     EAX: f34baac0  EBX: 00000090  ECX: f418deb0  EDX: f5542950  EBP: 00000000
>     DS:  007b      ESI: f34ba800  ES:  007b      EDI: f418dea0  GS:  00e0
>     CS:  0060      EIP: c046fa5e  ERR: ffffffff  EFLAGS: 00010286
>  #4 [f418de5c] add_timer at c046fa5e
>  #5 [f418de68] sctp_do_sm at f8db8c77 [sctp]
>  #6 [f418df30] sctp_primitive_SHUTDOWN at f8dcc1b5 [sctp]
>  #7 [f418df48] inet_shutdown at c080baf9
>  #8 [f418df5c] sys_shutdown at c079eedf
>  #9 [f418df70] sys_socketcall at c079fe88
>     EAX: ffffffda  EBX: 0000000d  ECX: bfceea90  EDX: 0937af98
>     DS:  007b      ESI: 0000000c  ES:  007b      EDI: b7150ae4
>     SS:  007b      ESP: bfceea7c  EBP: bfceeaa8  GS:  0033
>     CS:  0073      EIP: b775c424  ERR: 00000066  EFLAGS: 00000282
> 
> It appears that the side effect that starts the shutdown timer was processed
> multiple times, which can happen as multiple paths can trigger it.  This of
> course leads to the BUG halt in add_timer getting called.
> 
> Fix seems pretty straightforward, just check before the timer is added if its
> already been started.  If it has mod the timer instead to min(current
> expiration, new expiration)
> 
> Its been tested but not confirmed to fix the problem, as the issue has only
> occured in production environments where test kernels are enjoined from being
> installed.  It appears to be a sane fix to me though.  Also, recentely,
> Jere found a reproducer posted on list to confirm that this resolves the
> issues
> 
> Signed-off-by: Neil Horman <nhorman@...driver.com>
> CC: Vlad Yasevich <vyasevich@...il.com>
> CC: "David S. Miller" <davem@...emloft.net>
> CC: jere.leppanen@...ia.com
> CC: marcelo.leitner@...il.com
> CC: netdev@...r.kernel.org

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>

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