Date: Mon, 7 Mar 2022 13:17:56 -0800 From: Mark Millard <marklmi@yahoo.com> To: Ronald Klop <ronald-lists@klop.ws> Cc: Mark Johnston <markj@freebsd.org>, bob prohaska <fbsd@www.zefox.net>, Free BSD <freebsd-arm@freebsd.org>, freebsd-current <freebsd-current@freebsd.org> Subject: Re: panic: data abort in critical section or under mutex (was: Re: panic: Unknown kernel exception 0 esr_el1 2000000 (on 14-CURRENT/aarch64 Feb 28)) Message-ID: <E7675F09-6885-4924-B17D-C17AB1B70E05@yahoo.com> In-Reply-To: <1302689164.173.1646686466515@mailrelay> References: <C2F96211-0180-45DA-872F-52358D9ED35B.ref@yahoo.com> <C2F96211-0180-45DA-872F-52358D9ED35B@yahoo.com> <1800459695.1.1646649539521@mailrelay> <132978150.92.1646660769467@mailrelay> <YiYhIQXl1sd4cOVS@nuc> <1302689164.173.1646686466515@mailrelay>
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On 2022-Mar-7, at 12:54, Ronald Klop <ronald-lists@klop.ws> wrote: > Van: Mark Johnston <markj@freebsd.org> > Datum: maandag, 7 maart 2022 16:13 > Aan: Ronald Klop <ronald-lists@klop.ws> > CC: bob prohaska <fbsd@www.zefox.net>, Mark Millard = <marklmi@yahoo.com>, freebsd-arm@freebsd.org, freebsd-current = <freebsd-current@freebsd.org> > Onderwerp: Re: panic: data abort in critical section or under mutex = (was: Re: panic: Unknown kernel exception 0 esr_el1 2000000 (on = 14-CURRENT/aarch64 Feb 28)) >=20 > On Mon, Mar 07, 2022 at 02:46:09PM +0100, Ronald Klop wrote: > > Dear Mark Johnston, > > > > I did some binary search in the kernels and came to the conclusion = that = https://cgit.freebsd.org/src/commit/?id=3D1517b8d5a7f58897200497811de1b188= 09c07d3e still works and = https://cgit.freebsd.org/src/commit/?id=3D407c34e735b5d17e2be574808a09e6d7= 29b0a45a panics. > > > > I suspect your commit in = https://cgit.freebsd.org/src/commit/?id=3Dc84bb8cd771ce4bed58152e47a32dda4= 70bef23a. > > > > Last panic: > > > > panic: vm_fault failed: ffff00000046e708 error 1 > > cpuid =3D 1 > > time =3D 1646660058 > > KDB: stack backtrace: > > db_trace_self() at db_trace_self > > db_trace_self_wrapper() at db_trace_self_wrapper+0x30 > > vpanic() at vpanic+0x174 > > panic() at panic+0x44 > > data_abort() at data_abort+0x2e8 > > handle_el1h_sync() at handle_el1h_sync+0x10 > > --- exception, esr 0x96000004 > > _rm_rlock_debug() at _rm_rlock_debug+0x8c > > osd_get() at osd_get+0x5c > > zio_execute() at zio_execute+0xf8 > > taskqueue_run_locked() at taskqueue_run_locked+0x178 > > taskqueue_thread_loop() at taskqueue_thread_loop+0xc8 > > fork_exit() at fork_exit+0x74 > > fork_trampoline() at fork_trampoline+0x14 > > KDB: enter: panic > > [ thread pid 0 tid 100129 ] > > Stopped at kdb_enter+0x44: undefined f902011f > > db> > > > > A more recent kernel (912df91) still panics. See below. > > > > Do you have time to look into this? What can I provide in = information to help? >=20 > Hmm. So after my rmlock commits, we have the following disassembly = for > _rm_rlock() (with a few annotations added by me). Note that the pcpu > pointer is stored in register x18 by convention. >=20 > 0xffff00000046e304 <+0>: stp x29, x30, [sp, #-16]! > 0xffff00000046e308 <+4>: mov x29, sp > 0xffff00000046e30c <+8>: ldr x8, [x18] > 0xffff00000046e310 <+12>: ldr x9, [x18] > 0xffff00000046e314 <+16>: ldr x10, [x18] > 0xffff00000046e318 <+20>: cmp x9, x10 > 0xffff00000046e31c <+24>: b.ne 0xffff00000046e3cc = <_rm_rlock+200> // b.any > 0xffff00000046e320 <+28>: ldr x9, [x18] > 0xffff00000046e324 <+32>: ldrh w9, [x9, #314] > 0xffff00000046e328 <+36>: cbnz w9, 0xffff00000046e3c0 = <_rm_rlock+188> > 0xffff00000046e32c <+40>: str wzr, [x1, #32] > 0xffff00000046e330 <+44>: stp x0, x8, [x1, #16] > 0xffff00000046e334 <+48>: ldrb w9, [x0, #10] > 0xffff00000046e338 <+52>: tbz w9, #4, 0xffff00000046e358 = <_rm_rlock+84> > 0xffff00000046e33c <+56>: ldr x9, [x18] > 0xffff00000046e340 <+60>: ldr w10, [x9, #888] > 0xffff00000046e344 <+64>: add w10, w10, #0x1 > 0xffff00000046e348 <+68>: str w10, [x9, #888] > 0xffff00000046e34c <+72>: ldr x9, [x18] > 0xffff00000046e350 <+76>: ldr w9, [x9, #888] > 0xffff00000046e354 <+80>: cbz w9, 0xffff00000046e3f4 = <_rm_rlock+240> > 0xffff00000046e358 <+84>: ldr w9, [x8, #1212] > 0xffff00000046e35c <+88>: add x10, x18, #0x90 > 0xffff00000046e360 <+92>: add w9, w9, #0x1 > 0xffff00000046e364 <+96>: str w9, [x8, #1212] <------- = critical_enter > 0xffff00000046e368 <+100>: str x10, [x1, #8] > 0xffff00000046e36c <+104>: ldr x9, [x18, #144] > 0xffff00000046e370 <+108>: str x9, [x1] > 0xffff00000046e374 <+112>: str x1, [x9, #8] > 0xffff00000046e378 <+116>: str x1, [x18, #144] > 0xffff00000046e37c <+120>: ldr x9, [x18] > 0xffff00000046e380 <+124>: ldr w10, [x9, #356] > 0xffff00000046e384 <+128>: add w10, w10, #0x1 > 0xffff00000046e388 <+132>: str w10, [x9, #356] > 0xffff00000046e38c <+136>: ldr w9, [x8, #1212] > 0xffff00000046e390 <+140>: sub w9, w9, #0x1 > 0xffff00000046e394 <+144>: str w9, [x8, #1212] <------- = critical_exit > 0xffff00000046e398 <+148>: ldrb w8, [x8, #304] > 0xffff00000046e39c <+152>: ldr w9, [x18, #60] <------- = loading &pc->pc_cpuid > ... >=20 > A (the?) problem is that the compiler is treating "pc" as an alias > for x18, but the rmlock code assumes that the pcpu pointer is loaded > once, as it dereferences "pc" outside of the critical section. On > arm64, if a context switch occurs between the store at _rm_rlock+144 = and > the load at +152, and the thread is migrated to another CPU, then = we'll > end up using the wrong CPU ID in the rm->rm_writecpus test. >=20 > I suspect the problem is unique to arm64 as its get_pcpu() > implementation is different from the others in that it doesn't use > volatile-qualified inline assembly. This has been the case since > = https://cgit.freebsd.org/src/commit/?id=3D63c858a04d56529eddbddf85ad04fc8e= 99e73762 > . >=20 > I haven't been able to reproduce any crashes running poudriere in an > arm64 AWS instance, though. Could you please try the patch below and > confirm whether it fixes your panics? I verified that the apparent > problem described above is gone with the patch. >=20 > diff --git a/sys/kern/kern_rmlock.c b/sys/kern/kern_rmlock.c > index 0cdcfb8fec62..e51c25136ae0 100644 > --- a/sys/kern/kern_rmlock.c > +++ b/sys/kern/kern_rmlock.c > @@ -437,6 +437,7 @@ _rm_rlock(struct rmlock *rm, struct rm_priotracker = *tracker, int trylock) > { > struct thread *td =3D curthread; > struct pcpu *pc; > + int cpuid; > =20 > if (SCHEDULER_STOPPED()) > return (1); > @@ -452,6 +453,7 @@ _rm_rlock(struct rmlock *rm, struct rm_priotracker = *tracker, int trylock) > atomic_interrupt_fence(); > =20 > pc =3D get_pcpu(); > + cpuid =3D pc->pc_cpuid; > rm_tracker_add(pc, tracker); > sched_pin(); > =20 > @@ -463,7 +465,7 @@ _rm_rlock(struct rmlock *rm, struct rm_priotracker = *tracker, int trylock) > * conditional jump. > */ > if (__predict_true(0 =3D=3D (td->td_owepreempt | > - CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)))) > + CPU_ISSET(cpuid, &rm->rm_writecpus)))) > return (1); > =20 > /* We do not have a read token and need to acquire one. */ >=20 > Hi, >=20 > This patch paniced again: > x0: ffffa00005a31500 = =20 > x1: ffffa00005a0e000 = =20 > x2: 2 = =20 > x3: ffffa00076c4e9a0 = =20 > x4: 0 = =20 > x5: e672743c8f9e5 = =20 > x6: dc89f70500ab1 > x7: 14 > x8: ffffa00005a31518 > x9: 1 > x10: ffffa00005a0e000 > x11: 0 > x12: 0 > x13: a > x14: 1013e6b85a8ecbe4 > x15: 1dce740d11a5 > x16: ffff3ea86e2434bf > x17: fffffffffffffff2 > x18: ffff0000fe661800 (g_ctx + fcf9fa54) > x19: ffffa00076c4e9a0 > x20: ffff0000fec39000 (g_ctx + fd577254) > x21: 2 > x22: ffff0000419b6090 (g_ctx + 402f42e4) > x23: ffff000000c0b137 (lockstat_enabled + 0) > x24: 100 > x25: ffff000000c0b000 (version + a0) > x26: ffff000000c0b000 (version + a0) > x27: ffff000000c0b000 (version + a0) > x28: 0 > x29: ffff0000fe661800 (g_ctx + fcf9fa54) > sp: ffff0000fe661800 > lr: ffff00000154ea50 (zio_dva_throttle + 154) > elr: ffff00000154ea80 (zio_dva_throttle + 184) > spsr: 60000045 > far: 2b753286b0b8 > panic: Unknown kernel exception 0 esr_el1 2000000 > cpuid =3D 1 > time =3D 1646685857 > KDB: stack backtrace: > db_trace_self() at db_trace_self > db_trace_self_wrapper() at db_trace_self_wrapper+0x30 > vpanic() at vpanic+0x174 > panic() at panic+0x44 > do_el1h_sync() at do_el1h_sync+0x184 > handle_el1h_sync() at handle_el1h_sync+0x10 > --- exception, esr 0x2000000 > zio_dva_throttle() at zio_dva_throttle+0x184 > zio_execute() at zio_execute+0x58 > KDB: enter: panic > [ thread pid 0 tid 100129 ] > Stopped at kdb_enter+0x44: undefined f901c11f > db> =20 Hmm. My somewhat older source code shows zio_dva_throttle as having: mutex_enter(&spa->spa_allocs[allocator].spaa_lock); avl_add(&spa->spa_allocs[allocator].spaa_tree, zio); nio =3D zio_io_to_allocate(spa, allocator); mutex_exit(&spa->spa_allocs[allocator].spaa_lock); return (nio); That might have implications if the issue is actually analogous to _rm_rlock_debug crashes in some way. =3D=3D=3D Mark Millard marklmi at yahoo.com
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