On Tue, Apr 28, 2020 at 12:58:48PM -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@xxxxxxxxxxxxx>
> CC: Vlad Yasevich <vyasevich@xxxxxxxxx>
> CC: "David S. Miller" <davem@xxxxxxxxxxxxx>
> CC: Jere Leppänen <jere.leppanen@xxxxxxxxx>
> CC: marcelo.leitner@xxxxxxxxx
> ---
> net/sctp/sm_sideeffect.c | 21 ++++++++++++++++++---
> 1 file changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
> index 2bc29463e1dc..43a256b5a5f0 100644
> --- a/net/sctp/sm_sideeffect.c
> +++ b/net/sctp/sm_sideeffect.c
> @@ -1523,9 +1523,24 @@ static int sctp_cmd_interpreter(enum sctp_event_type event_type,
> timeout = asoc->timeouts[cmd->obj.to];
> BUG_ON(!timeout);
>
> - timer->expires = jiffies + timeout;
> - sctp_association_hold(asoc);
> - add_timer(timer);
> + /*
> + * SCTP has a hard time with timer starts. Because we process
> + * timer starts as side effects, it can be hard to tell if we
> + * have already started a timer or not, which leads to BUG
> + * halts when we call add_timer. So here, instead of just starting
> + * a timer, if the timer is already started, and just mod
> + * the timer with the shorter of the two expiration times
> + */
> + if (timer_pending(timer)) {
> + if (time_after(timer->expires, (jiffies + timeout))) {
> + timer->expires = jiffies+timeout;
> + mod_timer(timer, timer->expires);
> + }
> + } else {
> + timer->expires = jiffies + timeout;
> + sctp_association_hold(asoc);
> + mod_timer(timer, timer->expires);
> + }
Jere, can you then update it to use timer_reduce(), as you had
suggested?
> break;
>
> case SCTP_CMD_TIMER_RESTART:
> --
> 2.25.3
>
