Date: Wed, 11 Nov 2015 01:05:18 +0700 From: Eugene Grosbein <eugen@grosbein.net> To: Adrian Chadd <adrian@freebsd.org> Cc: "freebsd-mips@freebsd.org" <freebsd-mips@freebsd.org> Subject: Re: USB-related problem Message-ID: <564231DE.7090308@grosbein.net> In-Reply-To: <CAJ-VmomA27NcNCjx00DrZzFOU9bGYucUhbPXodH2uvNd8eJ3wg@mail.gmail.com> References: <56348063.3090508@grosbein.net> <CAJ-VmomtJ9eKfAJYfn4e2S1xWN8-YHo0M0KH-9V=VjNBf6vVVA@mail.gmail.com> <563707A0.3040700@grosbein.net> <CANCZdfrB0hkjmTU-9NzimBv=X_h-=bF0D2azBxg=9B=kmitv7Q@mail.gmail.com> <56370E1D.3040801@grosbein.net> <CAJ-Vmo=0vOAq8db_GeLWmdXr7xJdzUh44ZZJrQ9vVdpvzT9hiQ@mail.gmail.com> <563F5630.2000407@grosbein.net> <563F6F6F.1010807@grosbein.net> <CAJ-Vmo=fPSi7yZO5Xjodg8HPtTLd44Y9Y_8qg4EgTGwEpHO10A@mail.gmail.com> <563F91A8.9080702@grosbein.net> <CAJ-VmomUvoUerMS20qQsQujcjULVA=_jaLp9Mh3fU1fEpdwzZA@mail.gmail.com> <CAJ-Vmo=eUUZ928KgQbyOi8EdDFSmxhjvDOyAMvfXsqwDbO96ng@mail.gmail.com> <5640C0FD.2040803@grosbein.net> <CAJ-Vmo=6mztfvvBd91LPO5H418K8vW=%2BLk=6V5Z_y5DHu7v7HA@mail.gmail.com> <5640F315.5020303@grosbein.net> <CAJ-VmokpWM=d%2BtEFv8a8eU91UimVZ9W8da2QkKCTDjd%2B2ZM_LQ@mail.gmail.com> <56410214.3070901@grosbein.net> <CAJ-Vmo=QUUkTfQ7pvr_V%2BCQ8zQWOoqp3H8hD9LUR8C5U-5N=Ag@mail.gmail.com> <CAJ-VmomA27NcNCjx00DrZzFOU9bGYucUhbPXodH2uvNd8eJ3wg@mail.gmail.com>
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On 10.11.2015 04:43, Adrian Chadd wrote:
> Hi,
>
> How much C do you know? Are you able to add some debugging to
> sched_sync() (which IIRC is the syncer thread) and work out where it's
> getting stuck and spinning?
I did. I've added new global kernel symbol, variable schedstat
so I can check its value using ddb. And it's always equals to 5
when deadlock occurs, discovering the loop:
--- sys/kern/vfs_subr.c.orig 2015-10-08 23:33:53.935440000 +0700
+++ sys/kern/vfs_subr.c 2015-11-11 01:01:06.248144000 +0700
@@ -1786,169 +1786,199 @@ sync_vnode(struct synclist *slp, struct
* Put us back on the worklist. The worklist
* routine will remove us from our current
* position and then add us back in at a later
* position.
*/
vn_syncer_add_to_worklist(*bo, syncdelay);
}
BO_UNLOCK(*bo);
vdrop(vp);
mtx_lock(&sync_mtx);
return (0);
}
static int first_printf = 1;
+volatile unsigned schedstate = 0;
+
/*
* System filesystem synchronizer daemon.
*/
static void
sched_sync(void)
{
struct synclist *next, *slp;
struct bufobj *bo;
long starttime;
struct thread *td = curthread;
int last_work_seen;
int net_worklist_len;
int syncer_final_iter;
int error;
last_work_seen = 0;
syncer_final_iter = 0;
syncer_state = SYNCER_RUNNING;
starttime = time_uptime;
td->td_pflags |= TDP_NORUNNINGBUF;
EVENTHANDLER_REGISTER(shutdown_pre_sync, syncer_shutdown, td->td_proc,
SHUTDOWN_PRI_LAST);
+ schedstate = 0;
mtx_lock(&sync_mtx);
for (;;) {
+ schedstate = 1;
+
if (syncer_state == SYNCER_FINAL_DELAY &&
syncer_final_iter == 0) {
mtx_unlock(&sync_mtx);
kproc_suspend_check(td->td_proc);
mtx_lock(&sync_mtx);
}
+ schedstate = 2;
+
net_worklist_len = syncer_worklist_len - sync_vnode_count;
if (syncer_state != SYNCER_RUNNING &&
starttime != time_uptime) {
if (first_printf) {
printf("\nSyncing disks, vnodes remaining...");
first_printf = 0;
}
printf("%d ", net_worklist_len);
}
starttime = time_uptime;
/*
* Push files whose dirty time has expired. Be careful
* of interrupt race on slp queue.
*
* Skip over empty worklist slots when shutting down.
*/
do {
+ schedstate = 3;
slp = &syncer_workitem_pending[syncer_delayno];
syncer_delayno += 1;
if (syncer_delayno == syncer_maxdelay)
syncer_delayno = 0;
next = &syncer_workitem_pending[syncer_delayno];
/*
* If the worklist has wrapped since the
* it was emptied of all but syncer vnodes,
* switch to the FINAL_DELAY state and run
* for one more second.
*/
if (syncer_state == SYNCER_SHUTTING_DOWN &&
net_worklist_len == 0 &&
last_work_seen == syncer_delayno) {
syncer_state = SYNCER_FINAL_DELAY;
syncer_final_iter = SYNCER_SHUTDOWN_SPEEDUP;
}
} while (syncer_state != SYNCER_RUNNING && LIST_EMPTY(slp) &&
syncer_worklist_len > 0);
+ schedstate = 4;
+
/*
* Keep track of the last time there was anything
* on the worklist other than syncer vnodes.
* Return to the SHUTTING_DOWN state if any
* new work appears.
*/
if (net_worklist_len > 0 || syncer_state == SYNCER_RUNNING)
last_work_seen = syncer_delayno;
if (net_worklist_len > 0 && syncer_state == SYNCER_FINAL_DELAY)
syncer_state = SYNCER_SHUTTING_DOWN;
while (!LIST_EMPTY(slp)) {
+ schedstate = 5;
+
error = sync_vnode(slp, &bo, td);
if (error == 1) {
LIST_REMOVE(bo, bo_synclist);
LIST_INSERT_HEAD(next, bo, bo_synclist);
continue;
}
+ schedstate = 6;
if (first_printf == 0) {
+ schedstate = 7;
/*
* Drop the sync mutex, because some watchdog
* drivers need to sleep while patting
*/
mtx_unlock(&sync_mtx);
wdog_kern_pat(WD_LASTVAL);
mtx_lock(&sync_mtx);
}
+ schedstate = 8;
}
+ schedstate = 9;
+
if (syncer_state == SYNCER_FINAL_DELAY && syncer_final_iter > 0)
syncer_final_iter--;
/*
* The variable rushjob allows the kernel to speed up the
* processing of the filesystem syncer process. A rushjob
* value of N tells the filesystem syncer to process the next
* N seconds worth of work on its queue ASAP. Currently rushjob
* is used by the soft update code to speed up the filesystem
* syncer process when the incore state is getting so far
* ahead of the disk that the kernel memory pool is being
* threatened with exhaustion.
*/
if (rushjob > 0) {
rushjob -= 1;
continue;
}
/*
* Just sleep for a short period of time between
* iterations when shutting down to allow some I/O
* to happen.
*
* If it has taken us less than a second to process the
* current work, then wait. Otherwise start right over
* again. We can still lose time if any single round
* takes more than two seconds, but it does not really
* matter as we are just trying to generally pace the
* filesystem activity.
*/
+
+ schedstate = 10;
+
if (syncer_state != SYNCER_RUNNING ||
time_uptime == starttime) {
+ schedstate = 11;
thread_lock(td);
sched_prio(td, PPAUSE);
thread_unlock(td);
}
- if (syncer_state != SYNCER_RUNNING)
+ schedstate = 12;
+
+ if (syncer_state != SYNCER_RUNNING) {
+ schedstate = 13;
+
cv_timedwait(&sync_wakeup, &sync_mtx,
hz / SYNCER_SHUTDOWN_SPEEDUP);
- else if (time_uptime == starttime)
+ }
+ else if (time_uptime == starttime) {
+ schedstate = 14;
cv_timedwait(&sync_wakeup, &sync_mtx, hz);
+ }
+ schedstate = 15;
}
+ schedstate = 16;
}
/*
* Request the syncer daemon to speed up its work.
* We never push it to speed up more than half of its
* normal turn time, otherwise it could take over the cpu.
*/
int
speedup_syncer(void)
{
int ret = 0;
mtx_lock(&sync_mtx);
if (rushjob < syncdelay / 2) {
rushjob += 1;
help
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