This BUG halt was recently reported:
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.
Signed-off-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
CC: Vlad Yasevich <vyasevich@xxxxxxxxx>
CC: "David S. Miller" <davem@xxxxxxxxxxxxx>
Change notes:
v2) Removed WARN_ON, as its not useful
v3) Actually commit my changes
v4) Reduce code size by rolling expiration update into mod_timer line
---
net/sctp/sm_sideeffect.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
index b5327bb..192ec99 100644
--- a/net/sctp/sm_sideeffect.c
+++ b/net/sctp/sm_sideeffect.c
@@ -1480,9 +1480,21 @@ static int sctp_cmd_interpreter(sctp_event_t 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, just determine the shorter of the two
+ * timeouts and mod the timer to that.
+ */
+ if (timer_pending(timer)) {
+ if (time_after(timer->expires, (jiffies + timeout)))
+ mod_timer(timer, jiffies + timeout);
+ } else {
+ sctp_association_hold(asoc);
+ mod_timer(timer, jiffies + timeout);
+ }
break;
case SCTP_CMD_TIMER_RESTART:
--
2.5.5
--
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