On Tue, Sep 20, 2016 at 10:00:25PM +0200, Julien Charbon wrote:
>
> Hi Slawa,
>
> On 9/19/16 10:43 PM, Slawa Olhovchenkov wrote:
> > On Mon, Sep 19, 2016 at 10:32:13PM +0200, Julien Charbon wrote:
> >>
> >>> @ CPU_CLK_UNHALTED_CORE [4653445 samples]
> >>>
> >>> 51.86% [2413083] lock_delay @ /boot/kernel.VSTREAM/kernel
> >>> 100.0% [2413083] __rw_wlock_hard
> >>> 100.0% [2413083] tcp_tw_2msl_scan
> >>> 99.99% [2412958] pfslowtimo
> >>> 100.0% [2412958] softclock_call_cc
> >>> 100.0% [2412958] softclock
> >>> 100.0% [2412958] intr_event_execute_handlers
> >>> 100.0% [2412958] ithread_loop
> >>> 100.0% [2412958] fork_exit
> >>> 00.01% [125] tcp_twstart
> >>> 100.0% [125] tcp_do_segment
> >>> 100.0% [125] tcp_input
> >>> 100.0% [125] ip_input
> >>> 100.0% [125] swi_net
> >>> 100.0% [125] intr_event_execute_handlers
> >>> 100.0% [125] ithread_loop
> >>> 100.0% [125] fork_exit
> >>
> >> The only write lock tcp_tw_2msl_scan() tries to get is a
> >> INP_WLOCK(inp). Thus here, tcp_tw_2msl_scan() seems to be stuck
> >> spinning on INP_WLOCK (or pfslowtimo() is going crazy and calls
> >> tcp_tw_2msl_scan() at high rate but this will be quite unexpected).
> >>
> >> Thus my hypothesis is that something is holding the INP_WLOCK and not
> >> releasing it, and tcp_tw_2msl_scan() is spinning on it.
> >>
> >> If you can, could you compile the kernel with below options:
> >>
> >> options DDB # Support DDB.
> >> options DEADLKRES # Enable the deadlock resolver
> >> options INVARIANTS # Enable calls of extra sanity
> >> checking
> >> options INVARIANT_SUPPORT # Extra sanity checks of internal
> >> structures, required by INVARIANTS
> >> options WITNESS # Enable checks to detect
> >> deadlocks and cycles
> >> options WITNESS_SKIPSPIN # Don't run witness on spinlocks
> >> for speed
> >
> > Currently this host run with 100% CPU load (on all cores), i.e.
> > enabling WITNESS will be significant drop performance.
> > Can I use only some subset of options?
> >
> > Also, I can some troubles to DDB enter in this case.
> > May be kgdb will be success (not tryed yet)?
>
> If these kernel options will certainly slow down your kernel, they also
> might found the root cause of your issue before reaching the point where
> you have 100% cpu load on all cores (thanks to INVARIANTS). I would
> suggest:
Hmmm, may be I am not clarified.
This host run at peak hours with 100% CPU load as normal operation,
this is for servering 2x10G, this is CPU load not result of lock
issuse, this is not us case. And this is because I am fear to enable
WITNESS -- I am fear drop performance.
This lock issuse happen irregulary and may be caused by other issuse
(nginx crashed). In this case about 1/3 cores have 100% cpu load,
perhaps by this lock -- I am can trace only from one core and need
more then hour for this (may be on other cores different trace, I
can't guaranted anything).
> #1. Try above kernel options at least once, and see what you can get.
OK, I am try this after some time.
> #2. If #1 is a total failure try below patch: It won't solve anything,
> it just makes tcp_tw_2msl_scan() less greedy when there is contention on
> the INP write lock. If it makes the debugging more feasible, continue
> to #3.
OK, thanks.
What purpose to not skip locked tcptw in this loop?
> diff --git a/sys/netinet/tcp_timewait.c b/sys/netinet/tcp_timewait.c
> index a8b78f9..4206ea3 100644
> --- a/sys/netinet/tcp_timewait.c
> +++ b/sys/netinet/tcp_timewait.c
> @@ -701,34 +701,42 @@ tcp_tw_2msl_scan(int reuse)
> in_pcbref(inp);
> TW_RUNLOCK(V_tw_lock);
>
> +retry:
> if (INP_INFO_TRY_RLOCK(&V_tcbinfo)) {
>
> - INP_WLOCK(inp);
> - tw = intotw(inp);
> - if (in_pcbrele_wlocked(inp)) {
> - KASSERT(tw == NULL, ("%s: held last inp "
> - "reference but tw not NULL", __func__));
> - INP_INFO_RUNLOCK(&V_tcbinfo);
> - continue;
> - }
> + if (INP_TRY_WLOCK(inp)) {
> + tw = intotw(inp);
> + if (in_pcbrele_wlocked(inp)) {
> + KASSERT(tw == NULL, ("%s: held
> last inp "
> + "reference but tw not NULL",
> __func__));
> + INP_INFO_RUNLOCK(&V_tcbinfo);
> + continue;
> + }
>
> - if (tw == NULL) {
> - /* tcp_twclose() has already been called */
> - INP_WUNLOCK(inp);
> - INP_INFO_RUNLOCK(&V_tcbinfo);
> - continue;
> - }
> + if (tw == NULL) {
> + /* tcp_twclose() has already
> been called */
> + INP_WUNLOCK(inp);
> + INP_INFO_RUNLOCK(&V_tcbinfo);
> + continue;
> + }
>
> - tcp_twclose(tw, reuse);
> - INP_INFO_RUNLOCK(&V_tcbinfo);
> - if (reuse)
> - return tw;
> + tcp_twclose(tw, reuse);
> + INP_INFO_RUNLOCK(&V_tcbinfo);
> + if (reuse)
> + return tw;
> + } else {
> + INP_INFO_RUNLOCK(&V_tcbinfo);
> + goto retry;
> + }
> } else {
> /* INP_INFO lock is busy, continue later. */
> - INP_WLOCK(inp);
> - if (!in_pcbrele_wlocked(inp))
> - INP_WUNLOCK(inp);
> - break;
> + if (INP_TRY_WLOCK(inp)) {
> + if (!in_pcbrele_wlocked(inp))
> + INP_WUNLOCK(inp);
> + break;
> + } else {
> + goto retry;
> + }
> }
> }
>
> #3. Once the issue is reproduced, launch ddb and run the below commands:
>
> show pcpu
> show allpcpu
> show locks
> show alllocks
> show lockchain
> show allchains
> show all trace
>
> My 2 cents.
>
> --
> Julien
>
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