Re: NFS-exported ZFS instability
on 30/01/2013 00:44 Andriy Gapon said the following: on 29/01/2013 23:44 Hiroki Sato said the following: http://people.allbsd.org/~hrs/FreeBSD/pool-20130130.txt http://people.allbsd.org/~hrs/FreeBSD/pool-20130130-info.txt [snip] See tid 100153 (arc reclaim thread), tid 100105 (pagedaemon) and tid 100639 (nfsd in kmem_back). I decided to write a few more words about this issue. I think that the root cause of the problem is that ZFS ARC code performs memory allocations with M_WAITOK while holding some ARC lock(s). If a thread runs into such an allocation when a system is very low on memory (even for a very short period of time), then the thread is going to be blocked (to sleep in more exact terms) in VM_WAIT until a certain amount of memory is freed. To be more precise until v_free_count + v_cache_count goes above v_free_min. And quoting from the report: db show page cnt.v_free_count: 8842 cnt.v_cache_count: 0 cnt.v_inactive_count: 0 cnt.v_active_count: 169 cnt.v_wire_count: 6081952 cnt.v_free_reserved: 7981 cnt.v_free_min: 38435 cnt.v_free_target: 161721 cnt.v_cache_min: 161721 cnt.v_inactive_target: 242581 In this case tid 100639 is the thread: Tracing command nfsd pid 961 tid 100639 td 0xfe0027038920 sched_switch() at sched_switch+0x17a/frame 0xff86ca5c9c80 mi_switch() at mi_switch+0x1f8/frame 0xff86ca5c9cd0 sleepq_switch() at sleepq_switch+0x123/frame 0xff86ca5c9d00 sleepq_wait() at sleepq_wait+0x4d/frame 0xff86ca5c9d30 _sleep() at _sleep+0x3d4/frame 0xff86ca5c9dc0 kmem_back() at kmem_back+0x1a3/frame 0xff86ca5c9e50 kmem_malloc() at kmem_malloc+0x1f8/frame 0xff86ca5c9ea0 uma_large_malloc() at uma_large_malloc+0x4a/frame 0xff86ca5c9ee0 malloc() at malloc+0x14d/frame 0xff86ca5c9f20 arc_get_data_buf() at arc_get_data_buf+0x1f4/frame 0xff86ca5c9f60 arc_read_nolock() at arc_read_nolock+0x208/frame 0xff86ca5ca010 arc_read() at arc_read+0x93/frame 0xff86ca5ca090 dbuf_read() at dbuf_read+0x452/frame 0xff86ca5ca150 dmu_buf_hold_array_by_dnode() at dmu_buf_hold_array_by_dnode+0x16a/frame 0xff86ca5ca1e0 dmu_buf_hold_array() at dmu_buf_hold_array+0x67/frame 0xff86ca5ca240 dmu_read_uio() at dmu_read_uio+0x3f/frame 0xff86ca5ca2a0 zfs_freebsd_read() at zfs_freebsd_read+0x3e9/frame 0xff86ca5ca3b0 nfsvno_read() at nfsvno_read+0x2db/frame 0xff86ca5ca490 nfsrvd_read() at nfsrvd_read+0x3ff/frame 0xff86ca5ca710 nfsrvd_dorpc() at nfsrvd_dorpc+0xc9/frame 0xff86ca5ca910 nfssvc_program() at nfssvc_program+0x5da/frame 0xff86ca5caaa0 svc_run_internal() at svc_run_internal+0x5fb/frame 0xff86ca5cabd0 svc_thread_start() at svc_thread_start+0xb/frame 0xff86ca5cabe0 Sleeping in VM_WAIT while holding the ARC lock(s) means that other ARC operations may get blocked. And pretty much all ZFS I/O goes through the ARC. So that's why we see all those stuck nfsd threads. Another factor greatly contributing to the problem is that currently the page daemon blocks (sleeps) in arc_lowmem (a vm_lowmem hook) waiting for the ARC reclaim thread to make a pass. This happens before the page daemon makes its own pageout pass. But because tid 100639 holds the ARC lock(s), ARC reclaim thread gets blocked and can not make any forward progress. Thus the page daemon also gets blocked. And thus the page daemon can not free up any pages. So, this situation is not a true deadlock. E.g. it is theoretically possible that some other threads would free some memory at their own will and the condition would clear up. But in practice this is highly unlikely. Some possible resolutions that I can think of. The best one is probably doing ARC memory allocations without holding any locks. Also, maybe we should make a rule that no vm_lowmem hooks should sleep. That is, arc_lowmem should signal the ARC reclaim thread to do some work, but should not wait on it. Perhaps we could also provide a mechanism to mark certain memory allocations as special and use that mechanism for ARC allocations. So that VM_WAIT unblocks sooner: in this case we had 8842 free pages (~35MB), but thread 100639 was not waken up. I think that ideally we should do something about all the three directions. But even one of them might turn out to be sufficient. As I've said, the first one seems to be the most promising, but it would require some tricky programming (flags and retries?) to move memory allocations out of locked sections. -- Andriy Gapon ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org
Re: NFS-exported ZFS instability
Andriy Gapon wrote: on 30/01/2013 00:44 Andriy Gapon said the following: on 29/01/2013 23:44 Hiroki Sato said the following: http://people.allbsd.org/~hrs/FreeBSD/pool-20130130.txt http://people.allbsd.org/~hrs/FreeBSD/pool-20130130-info.txt [snip] See tid 100153 (arc reclaim thread), tid 100105 (pagedaemon) and tid 100639 (nfsd in kmem_back). I decided to write a few more words about this issue. I think that the root cause of the problem is that ZFS ARC code performs memory allocations with M_WAITOK while holding some ARC lock(s). If a thread runs into such an allocation when a system is very low on memory (even for a very short period of time), then the thread is going to be blocked (to sleep in more exact terms) in VM_WAIT until a certain amount of memory is freed. To be more precise until v_free_count + v_cache_count goes above v_free_min. And quoting from the report: db show page cnt.v_free_count: 8842 cnt.v_cache_count: 0 cnt.v_inactive_count: 0 cnt.v_active_count: 169 cnt.v_wire_count: 6081952 cnt.v_free_reserved: 7981 cnt.v_free_min: 38435 cnt.v_free_target: 161721 cnt.v_cache_min: 161721 cnt.v_inactive_target: 242581 In this case tid 100639 is the thread: Tracing command nfsd pid 961 tid 100639 td 0xfe0027038920 sched_switch() at sched_switch+0x17a/frame 0xff86ca5c9c80 mi_switch() at mi_switch+0x1f8/frame 0xff86ca5c9cd0 sleepq_switch() at sleepq_switch+0x123/frame 0xff86ca5c9d00 sleepq_wait() at sleepq_wait+0x4d/frame 0xff86ca5c9d30 _sleep() at _sleep+0x3d4/frame 0xff86ca5c9dc0 kmem_back() at kmem_back+0x1a3/frame 0xff86ca5c9e50 kmem_malloc() at kmem_malloc+0x1f8/frame 0xff86ca5c9ea0 uma_large_malloc() at uma_large_malloc+0x4a/frame 0xff86ca5c9ee0 malloc() at malloc+0x14d/frame 0xff86ca5c9f20 arc_get_data_buf() at arc_get_data_buf+0x1f4/frame 0xff86ca5c9f60 arc_read_nolock() at arc_read_nolock+0x208/frame 0xff86ca5ca010 arc_read() at arc_read+0x93/frame 0xff86ca5ca090 dbuf_read() at dbuf_read+0x452/frame 0xff86ca5ca150 dmu_buf_hold_array_by_dnode() at dmu_buf_hold_array_by_dnode+0x16a/frame 0xff86ca5ca1e0 dmu_buf_hold_array() at dmu_buf_hold_array+0x67/frame 0xff86ca5ca240 dmu_read_uio() at dmu_read_uio+0x3f/frame 0xff86ca5ca2a0 zfs_freebsd_read() at zfs_freebsd_read+0x3e9/frame 0xff86ca5ca3b0 nfsvno_read() at nfsvno_read+0x2db/frame 0xff86ca5ca490 nfsrvd_read() at nfsrvd_read+0x3ff/frame 0xff86ca5ca710 nfsrvd_dorpc() at nfsrvd_dorpc+0xc9/frame 0xff86ca5ca910 nfssvc_program() at nfssvc_program+0x5da/frame 0xff86ca5caaa0 svc_run_internal() at svc_run_internal+0x5fb/frame 0xff86ca5cabd0 svc_thread_start() at svc_thread_start+0xb/frame 0xff86ca5cabe0 Sleeping in VM_WAIT while holding the ARC lock(s) means that other ARC operations may get blocked. And pretty much all ZFS I/O goes through the ARC. So that's why we see all those stuck nfsd threads. Another factor greatly contributing to the problem is that currently the page daemon blocks (sleeps) in arc_lowmem (a vm_lowmem hook) waiting for the ARC reclaim thread to make a pass. This happens before the page daemon makes its own pageout pass. But because tid 100639 holds the ARC lock(s), ARC reclaim thread gets blocked and can not make any forward progress. Thus the page daemon also gets blocked. And thus the page daemon can not free up any pages. So, this situation is not a true deadlock. E.g. it is theoretically possible that some other threads would free some memory at their own will and the condition would clear up. But in practice this is highly unlikely. Some possible resolutions that I can think of. The best one is probably doing ARC memory allocations without holding any locks. Also, maybe we should make a rule that no vm_lowmem hooks should sleep. That is, arc_lowmem should signal the ARC reclaim thread to do some work, but should not wait on it. Perhaps we could also provide a mechanism to mark certain memory allocations as special and use that mechanism for ARC allocations. So that VM_WAIT unblocks sooner: in this case we had 8842 free pages (~35MB), but thread 100639 was not waken up. I think that ideally we should do something about all the three directions. But even one of them might turn out to be sufficient. As I've said, the first one seems to be the most promising, but it would require some tricky programming (flags and retries?) to move memory allocations out of locked sections. For the NFSv4 stuff, I pre-allocate any structures that I might need using malloc(..M_WAITOK) before going into the locked region. If I don't need them, I just free() them at the end. (I assign newp the allocation and set newp NULL if it is used. If newp != NULL at the end, then free(newp..);) This avoids all the go back and retry after doing an allocation complexity. (One of the big names, maybe Dykstra, had a name
Re: NFS-exported ZFS instability
on 30/01/2013 01:06 Rick Macklem said the following: Andriy Gapon wrote: on 29/01/2013 23:44 Hiroki Sato said the following: http://people.allbsd.org/~hrs/FreeBSD/pool-20130130.txt http://people.allbsd.org/~hrs/FreeBSD/pool-20130130-info.txt I recognize here a ZFS ARC deadlock that should have been prevented by r241773 and its MFCs (r242858 for 9, r242859 for 8). Unfortunately, pool-20130130-info.txt shows a kernel built from r244417, unless I somehow misread it. You are right. I slightly misdiagnosed the problem - it's not the same, but a slightly different problem. So it has almost the same cause, but r241773 didn't handle this situation. Basically: - a thread goes into ARC, acquires some ARC lock and then calls malloc(M_WAITOK) - there is a page shortage, so the thread ends up in VM_WAIT() waiting on pagedaemon - pagedaemon synchronously invokes lowmem hook - the ARC hook sleeps waiting on ARC reclaim thread to make a pass - ARC reclaim thread is blocked on the ARC lock held by the original thread My conclusion: ARC lowmem hook should never wait on ARC reclaim thread. At least as long as the ARC code calls malloc(M_WAITOK) while holding locks. Perhaps the root cause here is that we treat both KM_PUSHPAGE and KM_SLEEP as M_WAITOK. We do not seem to have an equivalent of KM_PUSHPAGE? Perhaps resurrected M_USE_RESERVE could serve this role? Quote: A small pool of reserved memory is available to allow the system to progress toward the goal of freeing additional memory while in a low memory situation. The KM_PUSHPAGE flag enables use of this reserved memory pool on an allocation. This flag can be used by drivers that implement strategy(9E) on memory allocations associated with a single I/O operation. The driver guarantees that the I/O operation will complete (or timeout) and, on completion, that the memory will be returned. The KM_PUSHPAGE flag should be used only in kmem_cache_alloc() calls. All allocations from a given cache should be consistent in their use of the flag. A driver that adheres to these restrictions can guarantee progress in a low memory situation without resorting to complex private allocation and queuing schemes. If KM_PUSHPAGE is specified, KM_SLEEP can also be used without causing deadlock. But please note how the Solaris API allows to use KM_PUSHPAGE with KM_SLEEP, not sure what's going on under the hood in that case. See tid 100153 (arc reclaim thread), tid 100105 (pagedaemon) and tid 100639 (nfsd in kmem_back). -- Andriy Gapon -- Andriy Gapon ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org
Re: NFS-exported ZFS instability
Andriy Gapon wrote: on 30/01/2013 01:06 Rick Macklem said the following: Andriy Gapon wrote: on 29/01/2013 23:44 Hiroki Sato said the following: http://people.allbsd.org/~hrs/FreeBSD/pool-20130130.txt http://people.allbsd.org/~hrs/FreeBSD/pool-20130130-info.txt I recognize here a ZFS ARC deadlock that should have been prevented by r241773 and its MFCs (r242858 for 9, r242859 for 8). Unfortunately, pool-20130130-info.txt shows a kernel built from r244417, unless I somehow misread it. You are right. I slightly misdiagnosed the problem - it's not the same, but a slightly different problem. So it has almost the same cause, but r241773 didn't handle this situation. Basically: - a thread goes into ARC, acquires some ARC lock and then calls malloc(M_WAITOK) - there is a page shortage, so the thread ends up in VM_WAIT() waiting on pagedaemon - pagedaemon synchronously invokes lowmem hook - the ARC hook sleeps waiting on ARC reclaim thread to make a pass - ARC reclaim thread is blocked on the ARC lock held by the original thread My conclusion: ARC lowmem hook should never wait on ARC reclaim thread. At least as long as the ARC code calls malloc(M_WAITOK) while holding locks. Perhaps the root cause here is that we treat both KM_PUSHPAGE and KM_SLEEP as M_WAITOK. We do not seem to have an equivalent of KM_PUSHPAGE? Perhaps resurrected M_USE_RESERVE could serve this role? Good work figuring this out! Obviously, better folk that I will have to figure out how to fix this. Good luck with it, rick ps: Having some special place malloc() can go for critical allocations, sounds like a good plan to me. Possibly have malloc() follow the M_NOWAIT path and then go to this area when M_NOWAIT fails to allocate? Quote: A small pool of reserved memory is available to allow the system to progress toward the goal of freeing additional memory while in a low memory situation. The KM_PUSHPAGE flag enables use of this reserved memory pool on an allocation. This flag can be used by drivers that implement strategy(9E) on memory allocations associated with a single I/O operation. The driver guarantees that the I/O operation will complete (or timeout) and, on completion, that the memory will be returned. The KM_PUSHPAGE flag should be used only in kmem_cache_alloc() calls. All allocations from a given cache should be consistent in their use of the flag. A driver that adheres to these restrictions can guarantee progress in a low memory situation without resorting to complex private allocation and queuing schemes. If KM_PUSHPAGE is specified, KM_SLEEP can also be used without causing deadlock. But please note how the Solaris API allows to use KM_PUSHPAGE with KM_SLEEP, not sure what's going on under the hood in that case. See tid 100153 (arc reclaim thread), tid 100105 (pagedaemon) and tid 100639 (nfsd in kmem_back). -- Andriy Gapon -- Andriy Gapon ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org
Re: NFS-exported ZFS instability
Hiroki Sato h...@freebsd.org wrote in 20130104.023244.472910818423317661@allbsd.org: hr Konstantin Belousov kostik...@gmail.com wrote hr in 20130102174044.gb82...@kib.kiev.ua: hr hr ko I might take a closer look this evening and see if I can spot anything hr ko in the log, rick hr ko ps: I hope Alan and Kostik don't mind being added to the cc list. hr ko hr ko What I see in the log is that the lock cascade rooted in the thread hr ko 100838, which owns system map mutex. I believe this prevents malloc(9) hr ko from making a progress in other threads, which e.g. own the ZFS vnode hr ko locks. As the result, the whole system wedged. hr ko hr ko Looking back at the thread 100838, we can see that it executes hr ko smp_tlb_shootdown(). It is impossible to tell from the static dump, hr ko is the appearance of the smp_tlb_shootdown() in the backtrace is hr ko transient, or the thread is spinning there, waiting for other CPUs to hr ko acknowledge the request. But, since the system wedged, most likely, hr ko smp_tlb_shootdown spins. hr ko hr ko Taking this hypothesis, the situation can occur, most likely, due to hr ko some other core running with the interrupts disabled. Inspection of the hr ko backtraces of the processes running on all cores does not show any which hr ko could legitimately own a spinlock or otherwise run with the interrupts hr ko disabled. hr ko hr ko One thing you could try to do is to enable WITNESS for the spinlocks, hr ko to try to catch the leaked spinlock. I very much doubt that this is hr ko the case. hr ko hr ko Another thing to try is to switch the CPU idle method to something hr ko else. Look at the machdep.idle* sysctls. It could be some CPU errata hr ko which blocks wakeup due the interrupt in some conditions in C1 ? hr hr Thank you. It can take 1-2 weeks to reproduce this, so I set hr debug.witness.skipspin=0 and keeping machdep.idle acpi abd will see hr how it goes for a while. I will report again if I can get another hr freeze. Hmm, I could reproduce the same freeze when debug.witness.skipspin=0, too. DDB and crash dump outputs are the following: http://people.allbsd.org/~hrs/FreeBSD/pool-20130130.txt http://people.allbsd.org/~hrs/FreeBSD/pool-20130130-info.txt The value of machdep.idle was acpi. I have seen this symptom on two boxes with the following CPUs, so I am guessing it is not specific to a CPU model: CPU: Intel(R) Pentium(R) D CPU 3.40GHz (3391.52-MHz K8-class CPU) CPU: Intel(R) Xeon(R) CPU X5650 @ 2.67GHz (2666.82-MHz K8-class CPU) -- Hiroki pgpD2om1nCoqH.pgp Description: PGP signature
Re: NFS-exported ZFS instability
on 29/01/2013 23:44 Hiroki Sato said the following: http://people.allbsd.org/~hrs/FreeBSD/pool-20130130.txt http://people.allbsd.org/~hrs/FreeBSD/pool-20130130-info.txt I recognize here a ZFS ARC deadlock that should have been prevented by r241773 and its MFCs (r242858 for 9, r242859 for 8). See tid 100153 (arc reclaim thread), tid 100105 (pagedaemon) and tid 100639 (nfsd in kmem_back). -- Andriy Gapon ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org
Re: NFS-exported ZFS instability
Andriy Gapon wrote: on 29/01/2013 23:44 Hiroki Sato said the following: http://people.allbsd.org/~hrs/FreeBSD/pool-20130130.txt http://people.allbsd.org/~hrs/FreeBSD/pool-20130130-info.txt I recognize here a ZFS ARC deadlock that should have been prevented by r241773 and its MFCs (r242858 for 9, r242859 for 8). Unfortunately, pool-20130130-info.txt shows a kernel built from r244417, unless I somehow misread it. rick See tid 100153 (arc reclaim thread), tid 100105 (pagedaemon) and tid 100639 (nfsd in kmem_back). -- Andriy Gapon ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org
Re: NFS-exported ZFS instability
Rick Macklem rmack...@uoguelph.ca wrote in 1914428061.1617223.1357133079421.javamail.r...@erie.cs.uoguelph.ca: rm Hiroki Sato wrote: rm Hello, rm rm I have been in a trouble about my NFS server for a long time. The rm symptom is that it stops working in one or two weeks after a boot. I rm could not track down the cause yet, but it is reproducible and only rm occurred under a very high I/O load. rm rm It did not panic, just stopped working---while it responded to ping, rm userland programs seemed not working. I could break it into DDB and rm get a kernel dump. The following URLs are a log of ps, trace, and rm etc.: rm rm http://people.allbsd.org/~hrs/FreeBSD/pool.log.20130102 rm http://people.allbsd.org/~hrs/FreeBSD/pool.dmesg.20130102 rm rm Does anyone see how to debug this? I guess this is due to a deadlock rm somewhere. I have suffered from this problem for almost two years. rm The above log is from stable/9 as of Dec 19, but this have persisted rm since 8.X. rm rm Well, I took a quick glance at the log and there are a lot of processes rm sleeping on pfault (in vm_waitpfault() in sys/vm/vm_page.c). I'm no rm vm guy, so I'm not sure when/why that will happen. The comment on the rm function suggests they are waiting for free pages. rm rm Maybe something as simple as running out of swap space or a problem rm talking to the disk(s) that has the swap partition(s) or ??? rm (I'm talking through my hat here, because I'm not conversant with rm the vm side of things.) rm rm I might take a closer look this evening and see if I can spot anything rm in the log, rick rm ps: I hope Alan and Kostik don't mind being added to the cc list. Thank you. This machine has 24GB RAM + 30GB swap. 16GB of them are used for ZFS ARC, and I can see 1.5GB free space on average. However, frequent swapouts happen in a regular basis even when the I/O load is low. The amount used in the swap was 20-30MB only regardless of the load. I checked vm.stats and the outputs of vmstat -z/-m every 10 sec until the freeze several times but vm.stats.vm.v_free_count was around 300,000 (1GB) even just before the freeze. -- Hiroki pgpt4cIux6h0I.pgp Description: PGP signature
Re: NFS-exported ZFS instability
Konstantin Belousov kostik...@gmail.com wrote in 20130102174044.gb82...@kib.kiev.ua: ko I might take a closer look this evening and see if I can spot anything ko in the log, rick ko ps: I hope Alan and Kostik don't mind being added to the cc list. ko ko What I see in the log is that the lock cascade rooted in the thread ko 100838, which owns system map mutex. I believe this prevents malloc(9) ko from making a progress in other threads, which e.g. own the ZFS vnode ko locks. As the result, the whole system wedged. ko ko Looking back at the thread 100838, we can see that it executes ko smp_tlb_shootdown(). It is impossible to tell from the static dump, ko is the appearance of the smp_tlb_shootdown() in the backtrace is ko transient, or the thread is spinning there, waiting for other CPUs to ko acknowledge the request. But, since the system wedged, most likely, ko smp_tlb_shootdown spins. ko ko Taking this hypothesis, the situation can occur, most likely, due to ko some other core running with the interrupts disabled. Inspection of the ko backtraces of the processes running on all cores does not show any which ko could legitimately own a spinlock or otherwise run with the interrupts ko disabled. ko ko One thing you could try to do is to enable WITNESS for the spinlocks, ko to try to catch the leaked spinlock. I very much doubt that this is ko the case. ko ko Another thing to try is to switch the CPU idle method to something ko else. Look at the machdep.idle* sysctls. It could be some CPU errata ko which blocks wakeup due the interrupt in some conditions in C1 ? Thank you. It can take 1-2 weeks to reproduce this, so I set debug.witness.skipspin=0 and keeping machdep.idle acpi abd will see how it goes for a while. I will report again if I can get another freeze. -- Hiroki pgppNW6a6Bds7.pgp Description: PGP signature
Re: NFS-exported ZFS instability
Hiroki Sato wrote: Hello, I have been in a trouble about my NFS server for a long time. The symptom is that it stops working in one or two weeks after a boot. I could not track down the cause yet, but it is reproducible and only occurred under a very high I/O load. It did not panic, just stopped working---while it responded to ping, userland programs seemed not working. I could break it into DDB and get a kernel dump. The following URLs are a log of ps, trace, and etc.: http://people.allbsd.org/~hrs/FreeBSD/pool.log.20130102 http://people.allbsd.org/~hrs/FreeBSD/pool.dmesg.20130102 Does anyone see how to debug this? I guess this is due to a deadlock somewhere. I have suffered from this problem for almost two years. The above log is from stable/9 as of Dec 19, but this have persisted since 8.X. Well, I took a quick glance at the log and there are a lot of processes sleeping on pfault (in vm_waitpfault() in sys/vm/vm_page.c). I'm no vm guy, so I'm not sure when/why that will happen. The comment on the function suggests they are waiting for free pages. Maybe something as simple as running out of swap space or a problem talking to the disk(s) that has the swap partition(s) or ??? (I'm talking through my hat here, because I'm not conversant with the vm side of things.) I might take a closer look this evening and see if I can spot anything in the log, rick ps: I hope Alan and Kostik don't mind being added to the cc list. -- Hiroki ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org
Re: NFS-exported ZFS instability
On Wed, Jan 02, 2013 at 08:24:39AM -0500, Rick Macklem wrote: Hiroki Sato wrote: Hello, I have been in a trouble about my NFS server for a long time. The symptom is that it stops working in one or two weeks after a boot. I could not track down the cause yet, but it is reproducible and only occurred under a very high I/O load. It did not panic, just stopped working---while it responded to ping, userland programs seemed not working. I could break it into DDB and get a kernel dump. The following URLs are a log of ps, trace, and etc.: http://people.allbsd.org/~hrs/FreeBSD/pool.log.20130102 http://people.allbsd.org/~hrs/FreeBSD/pool.dmesg.20130102 Does anyone see how to debug this? I guess this is due to a deadlock somewhere. I have suffered from this problem for almost two years. The above log is from stable/9 as of Dec 19, but this have persisted since 8.X. Well, I took a quick glance at the log and there are a lot of processes sleeping on pfault (in vm_waitpfault() in sys/vm/vm_page.c). I'm no vm guy, so I'm not sure when/why that will happen. The comment on the function suggests they are waiting for free pages. Maybe something as simple as running out of swap space or a problem talking to the disk(s) that has the swap partition(s) or ??? (I'm talking through my hat here, because I'm not conversant with the vm side of things.) I might take a closer look this evening and see if I can spot anything in the log, rick ps: I hope Alan and Kostik don't mind being added to the cc list. What I see in the log is that the lock cascade rooted in the thread 100838, which owns system map mutex. I believe this prevents malloc(9) from making a progress in other threads, which e.g. own the ZFS vnode locks. As the result, the whole system wedged. Looking back at the thread 100838, we can see that it executes smp_tlb_shootdown(). It is impossible to tell from the static dump, is the appearance of the smp_tlb_shootdown() in the backtrace is transient, or the thread is spinning there, waiting for other CPUs to acknowledge the request. But, since the system wedged, most likely, smp_tlb_shootdown spins. Taking this hypothesis, the situation can occur, most likely, due to some other core running with the interrupts disabled. Inspection of the backtraces of the processes running on all cores does not show any which could legitimately own a spinlock or otherwise run with the interrupts disabled. One thing you could try to do is to enable WITNESS for the spinlocks, to try to catch the leaked spinlock. I very much doubt that this is the case. Another thing to try is to switch the CPU idle method to something else. Look at the machdep.idle* sysctls. It could be some CPU errata which blocks wakeup due the interrupt in some conditions in C1 ? pgpE8MByHmYh5.pgp Description: PGP signature
Re: NFS-exported ZFS instability
Hiroki Sato h...@freebsd.org wrote: I have been in a trouble about my NFS server for a long time. The symptom is that it stops working in one or two weeks after a boot ... It did not panic, just stopped working---while it responded to ping, userland programs seemed not working ... Does anyone see how to debug this? I guess this is due to a deadlock somewhere ... If you can afford the overhead, you could try running with some of the kernel debug options enabled (e.g. WITNESS, INVARIANTS, MUTEX_DEBUG). See conf/NOTES for descriptions. ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org
