I am investigating a problem that originally looked like a ZFS I/O hang.
But it quickly became obvious that the GEOM "up" queue was not being processed.
(kgdb) p g_bio_run_up
$54 = {bio_queue = {tqh_first = 0xfffff801d8627178, tqh_last =
0xfffff80134751658}, bio_queue_lock = {lock_object = {lo_name =
0xffffffff80ad11ab "bio queue", lo_flags = 16973824, lo_data = 0, lo_witness =
0x0}, mtx_lock = 0}, bio_queue_length = 19}
The queue is unlocked and there are 19 bio-s on it.
At the same time:
(kgdb) tid 100125
(kgdb) bt
#0 sched_switch (td=0xfffff80111b23000, newtd=0xfffff801119d2000,
flags=<optimized out>) at /usr/src/sys/kern/sched_ule.c:1997
#1 0xffffffff80705405 in mi_switch (flags=<optimized out>, newtd=0x0) at
/usr/src/sys/kern/kern_synch.c:436
#2 0xffffffff8074844a in sleepq_wait (wchan=<unavailable>, pri=<unavailable>)
at /usr/src/sys/kern/subr_sleepqueue.c:694
#3 0xffffffff80704ed6 in _sleep (ident=0xffffffff81233d68 <g_wait_up>,
lock=0xffffffff810d72e0 <g_bio_run_up+16>, priority=<optimized out>,
wmesg=0xffffffff80b417e4 "-", sbt=0, pr=0, flags=256) at
/usr/src/sys/kern/kern_synch.c:216
#4 0xffffffff8067713c in g_io_schedule_up (tp=<optimized out>) at
/usr/src/sys/geom/geom_io.c:908
#5 0xffffffff8067772d in g_up_procbody (arg=<optimized out>) at
/usr/src/sys/geom/geom_kern.c:99
#6 0xffffffff806c64c1 in fork_exit (callout=0xffffffff806776c0 <g_up_procbody>,
arg=0x0, frame=0xfffffe014cc87ac0) at /usr/src/sys/kern/kern_fork.c:1042
The "g_up" thread is sleeping as if the queue was empty.
The code in g_io_schedule_up() and g_io_deliver() is obviously correct with
respect to synchronizing the queue access and wait/wakeup.
So, there must be something deeper.
I examined the struct thread and the related scheduling objects:
(kgdb) p *td
$57 = {td_lock = 0xffffffff810f3a00 <tdq_cpu+9792>, td_proc =
0xfffff801119cd590, td_plist = {tqe_next = 0xfffff80111b1f5e0, tqe_prev =
0xfffff80111b235f0}, td_runq = {tqe_next = 0x0,
tqe_prev = 0xffffffff810f3bd8 <tdq_cpu+10264>}, td_slpq = {tqe_next = 0x0,
tqe_prev = 0xfffff80100050280}, td_lockq = {tqe_next = 0x0, tqe_prev =
0xfffffe018e443998}, td_hash = {le_next = 0x0, le_prev = 0xfffffe014bab68e8},
td_cpuset = 0xfffff80111b3a618, td_domain = {dr_policy = 0xffffffff810d78d8
<domainset0>, dr_iterator = 0}, td_sel = 0x0, td_sleepqueue =
0xfffff80100050280, td_turnstile = 0xfffff801a7ed8a80, td_rlqe = 0x0,
td_umtxq = 0xfffff80111b13e80, td_tid = 100125, td_sigqueue = {sq_signals =
{__bits = {0, 0, 0, 0}}, sq_kill = {__bits = {0, 0, 0, 0}}, sq_ptrace = {__bits
= {0, 0, 0, 0}}, sq_list = {tqh_first = 0x0,
tqh_last = 0xfffff80111b230d8}, sq_proc = 0xfffff801119cd590, sq_flags =
1}, td_lend_user_pri = 255 '\377', td_flags = 4, td_inhibitors = 0, td_pflags =
2097152, td_dupfd = 0, td_sqqueue = 0, td_wchan = 0x0,
td_wmesg = 0x0, td_owepreempt = 0 '\000', td_tsqueue = 0 '\000', td_locks = 0,
td_rw_rlocks = 0, td_sx_slocks = 0, td_lk_slocks = 0, td_stopsched = 0,
td_blocked = 0x0, td_lockname = 0x0, td_contested = {lh_first = 0x0},
td_sleeplocks = 0x0, td_intr_nesting_level = 0, td_pinned = 0, td_ucred =
0xfffff80100082b00, td_limit = 0xfffff80100082a00, td_slptick = 0, td_blktick =
0, td_swvoltick = -2139537593, td_swinvoltick = -2139537706, td_cow = 0,
td_ru = {ru_utime = {tv_sec = 0, tv_usec = 0}, ru_stime = {tv_sec = 0, tv_usec
= 0}, ru_maxrss = 0, ru_ixrss = 0, ru_idrss = 0, ru_isrss = 0, ru_minflt = 0,
ru_majflt = 0, ru_nswap = 0, ru_inblock = 0, ru_oublock = 0,
ru_msgsnd = 0, ru_msgrcv = 0, ru_nsignals = 0, ru_nvcsw = 14113408,
ru_nivcsw = 240828}, td_rux = {rux_runtime = 202213463115, rux_uticks = 0,
rux_sticks = 10554, rux_iticks = 0, rux_uu = 0, rux_su = 36818497,
rux_tu = 36818497}, td_incruntime = 46828278, td_runtime = 202260266673,
td_pticks = 10557, td_sticks = 3, td_iticks = 0, td_uticks = 0, td_intrval = 0,
td_oldsigmask = {__bits = {0, 0, 0, 0}}, td_generation = 14354236,
td_sigstk = {ss_sp = 0x0, ss_size = 0, ss_flags = 0}, td_xsig = 0,
td_profil_addr = 0, td_profil_ticks = 0, td_name = "g_up", '\000' <repeats 15
times>, td_fpop = 0x0, td_dbgflags = 0, td_si = {si_signo = 0, si_errno = 0,
si_code = 0, si_pid = 0, si_uid = 0, si_status = 0, si_addr = 0x0, si_value
= {sival_int = 0, sival_ptr = 0x0, sigval_int = 0, sigval_ptr = 0x0}, _reason =
{_fault = {_trapno = 0}, _timer = {_timerid = 0, _overrun = 0},
_mesgq = {_mqd = 0}, _poll = {_band = 0}, __spare__ = {__spare1__ = 0,
__spare2__ = {0, 0, 0, 0, 0, 0, 0}}}}, td_ng_outbound = 0, td_osd = {osd_nslots
= 0, osd_slots = 0x0, osd_next = {le_next = 0x0, le_prev = 0x0}},
td_map_def_user = 0x0, td_dbg_forked = 0, td_vp_reserv = 0, td_no_sleeping =
0, td_su = 0x0, td_sleeptimo = 0, td_rtcgen = 0, td_sigmask = {__bits = {0, 0,
0, 0}}, td_rqindex = 23 '\027', td_base_pri = 92 '\\',
td_priority = 92 '\\', td_pri_class = 3 '\003', td_user_pri = 120 'x',
td_base_user_pri = 120 'x', td_rb_list = 0, td_rbp_list = 0, td_rb_inact = 0,
td_sa = {code = 0, callp = 0x0, args = {0 <repeats 16 times>}, narg = 0},
td_pcb = 0xfffffe014cc87b80, td_state = TDS_RUNQ, td_uretoff = {tdu_retval =
{0, 0}, tdu_off = 0}, td_cowgen = 0, td_slpcallout = {c_links = {le = {le_next =
0x0, le_prev = 0x0}, sle = {sle_next = 0x0}, tqe = {tqe_next = 0x0,
tqe_prev = 0x0}}, c_time = 0, c_precision = 0, c_arg = 0x0, c_func =
0x0, c_lock = 0x0, c_flags = 0, c_iflags = 16, c_cpu = 0, c_exec_time = 0,
c_lines = {u128 = 1481, u16 = {1481, 0, 0, 0, 0, 0, 0, 0}}},
td_frame = 0xfffffe014cc87ac0, td_kstack_obj = 0xfffff80111b31e00, td_kstack =
18446741880269406208, td_kstack_pages = 16, td_critnest = 1, td_md =
{md_spinlock_count = 1, md_saved_flags = 582, md_spurflt_addr = 0,
md_invl_gen = {gen = 0, link = {le_next = 0x0, le_prev = 0x0}}}, td_ar =
0x0, td_lprof = {{lh_first = 0x0}, {lh_first = 0x0}}, td_dtrace =
0xfffff80111aef700, td_errno = 0, td_vnet = 0x0, td_vnet_lpush = 0x0,
td_intr_frame = 0x0, td_rfppwait_p = 0x0, td_ma = 0x0, td_ma_cnt = 0,
td_emuldata = 0x0, td_lastcpu = 3, td_oncpu = -1, td_lkpi_task = 0x0}
(kgdb) p td->td_oncpu
$58 = -1
(kgdb) p *td->td_sleepqueue
$61 = {sq_blocked = {{tqh_first = 0x0, tqh_last = 0xfffff80100050280},
{tqh_first = 0x0, tqh_last = 0xfffff80100050290}}, sq_blockedcnt = {0, 0},
sq_hash = {le_next = 0xfffff807d069c380,
le_prev = 0xffffffff811c7c40 <sleepq_chains+38208>}, sq_free = {lh_first =
0x0}, sq_wchan = 0xffffffff81233d68 <g_wait_up>, sq_type = 0}
(kgdb) p *(struct td_sched *)&td[1]
$68 = {ts_runq = 0xffffffff810f3a60 <tdq_cpu+9888>, ts_flags = 2, ts_cpu = 3,
ts_rltick = -2139537593, ts_slice = 0, ts_slptime = 4601740, ts_runtime = 30146,
ts_ltick = -2139537587, ts_ftick = -2139547918, ts_ticks = 20239,
ts_name = "g_up tid 100125", '\000' <repeats 19 times>}
(kgdb) p tdq_cpu[3]
$70 = {tdq_lock = {lock_object = {lo_name = 0xffffffff810f4678 <tdq_cpu+12984>
"sched lock 3", lo_flags = 720896, lo_data = 0, lo_witness = 0x0}, mtx_lock =
0}, tdq_cg = 0xffffffff811ce8b0 <group+336>, tdq_load = 1,
tdq_cpu_idle = 1, tdq_sysload = 1, tdq_transferable = 1, tdq_switchcnt = 1,
tdq_oldswitchcnt = 26, tdq_lowpri = 92 '\\', tdq_ipipending = 0 '\000', tdq_idx
= 9 '\t', tdq_ridx = 9 '\t', tdq_realtime = { ...
What I see here:
- td_state = TDS_RUNQ -- so the thread is "kind of" woken up
- td_oncpu = -1 -- but not quite
- ts_cpu = 3 -- looks like it was placed on CPU3's run queue
- tdq_cpu_idle = 1 -- the CPU still "runs" its idle thread
So, if I am not confused, it appears like possibly a notification from a waking
CPU to the woken CPU (CPU3) was never delivered.
Potentially, a problem with cpu_idle_wakeup() ?
I wonder if there have been any bug fixes in that area over the past year or so.
Any help and pointers are welcome.
Thank you!
--
Andriy Gapon
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