Deadlock in NFSv4 in all kernels
in [Kernel]
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From: Lukas Hejtmanek on 7 May 2010 12:00 Hi, I encountered the following problem. We use short expiration time for kerberos contexts created by rpc.gssd (some patches were included in mainline nfs-utils). In particular, we use 120secs expiration time. Now, I run application that eats 80% of available RAM. Then I run 10 parallel dd processes that write data into NFS4 volume with sec=krb5. As soon as the kerberos context expires (i.e., up to 120 secs), the whole system gets stuck in do_page_fault and succesive functions. It is because there is no free memory in kernel, all free memory is used as cache for NFS4 (due to dd traffic), kernel ask NFS to write back its pages but NFS cannot do anything as it is missing valid context. NFS contacts rpc.gssd to provide a renewed context, the rpc.gssd does not provide the context as it needs some memory to scan /tmp for a ticket. I.e., it deadlocks. Longer context expiration time is no real solution as it only makes the deadlock less often. Any ideas what can be done here? (Please cc me.) We could preallocate some memory in rpc.gssd and use mlockall but not sure whether this proctects also kernel malloc for things related to rpc.gssd and context creation (new file descriptors and so on). This is seen in 2.6.32 kernel but most probably this is related to all kernel versions. rpc.gssd and all dd processes are stuck in: May 6 15:33:10 skirit20 kernel: [84087.788019] rpc.gssd D 6758d881 0 26864 1 0x00000000 May 6 15:33:10 skirit20 kernel: [84087.788019] c280594c 00000086 f94c3d6c 6758d881 00004c5a 0f3e1c27 c1d868c0 c1c068dc May 6 15:33:10 skirit20 kernel: [84087.788019] c07d8880 c07d8880 f6752130 f67523d4 c1c06880 00000000 c1c06880 00000000 May 6 15:33:10 skirit20 kernel: [84087.788019] f6d7c8f0 f67523d4 f6752130 c1c06cd4 c1c06880 c2805960 c052101f 00000000 May 6 15:33:10 skirit20 kernel: [84087.788019] Call Trace: May 6 15:33:10 skirit20 kernel: [84087.788019] [<c052101f>] io_schedule+0x6f/0xc0 May 6 15:33:10 skirit20 kernel: [84087.788019] [<f88d8af5>] nfs_wait_bit_uninterruptible+0x5/0x10 [nfs] May 6 15:33:10 skirit20 kernel: [84087.788019] [<c05215a7>] __wait_on_bit+0x47/0x70 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c0521683>] out_of_line_wait_on_bit+0xb3/0xd0 May 6 15:33:10 skirit20 kernel: [84087.788019] [<f88d8ae3>] nfs_wait_on_request+0x23/0x30 [nfs] May 6 15:33:10 skirit20 kernel: [84087.788019] [<f88ddb4a>] nfs_sync_mapping_wait+0xea/0x200 [nfs] May 6 15:33:10 skirit20 kernel: [84087.788019] [<f88ddd0e>] nfs_wb_page_priority+0xae/0x170 [nfs] May 6 15:33:10 skirit20 kernel: [84087.788019] [<f88cdfec>] nfs_release_page+0x5c/0x70 [nfs] May 6 15:33:10 skirit20 kernel: [84087.788019] [<c029620b>] try_to_release_page+0x2b/0x40 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c02a25af>] shrink_page_list+0x37f/0x4b0 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c02a29ae>] shrink_inactive_list+0x2ce/0x6c0 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c02a34c8>] shrink_zone+0x1c8/0x260 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c02a35ae>] shrink_zones+0x4e/0xe0 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c02a43b5>] do_try_to_free_pages+0x75/0x2e0 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c02a4756>] try_to_free_pages+0x86/0xa0 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c029cda4>] __alloc_pages_slowpath+0x164/0x470 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c029d1c8>] __alloc_pages_nodemask+0x118/0x120 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c02acce0>] do_anonymous_page+0x100/0x240 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c02b072a>] handle_mm_fault+0x34a/0x3d0 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c0524c54>] do_page_fault+0x174/0x370 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c0522cb6>] error_code+0x66/0x70 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c0296ac2>] file_read_actor+0x32/0xf0 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c029815f>] do_generic_file_read+0x3af/0x4c0 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c0298a01>] generic_file_aio_read+0xb1/0x210 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c02cdc05>] do_sync_read+0xd5/0x120 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c02ce3bb>] vfs_read+0x9b/0x110 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c02ce501>] sys_read+0x41/0x80 May 6 15:33:10 skirit20 kernel: [84087.788019] [<c0203150>] sysenter_do_call+0x12/0x22 May 6 15:33:10 skirit20 kernel: [84087.788019] [<ffffe430>] 0xffffe430 -- Luk� Hejtm�nek -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Pavel Machek on 25 May 2010 04:00 Hi! > I encountered the following problem. We use short expiration time for > kerberos contexts created by rpc.gssd (some patches were included in mainline > nfs-utils). In particular, we use 120secs expiration time. > > Now, I run application that eats 80% of available RAM. Then I run 10 parallel > dd processes that write data into NFS4 volume with sec=krb5. > > As soon as the kerberos context expires (i.e., up to 120 secs), the whole > system gets stuck in do_page_fault and succesive functions. It is because > there is no free memory in kernel, all free memory is used as cache for NFS4 > (due to dd traffic), kernel ask NFS to write back its pages but NFS cannot do > anything as it is missing valid context. NFS contacts rpc.gssd to provide > a renewed context, the rpc.gssd does not provide the context as it needs some memory > to scan /tmp for a ticket. I.e., it deadlocks. > > Longer context expiration time is no real solution as it only makes the > deadlock less often. > > Any ideas what can be done here? (Please cc me.) We could preallocate some > memory in rpc.gssd and use mlockall but not sure whether this proctects also > kernel malloc for things related to rpc.gssd and context creation (new file > descriptors and so on). > > This is seen in 2.6.32 kernel but most probably this is related to all kernel > versions. Seems like pretty fundamental problem in nfs :-(. Limiting writeback caches for nfs, so that system has enough memory to perform rpc calls with the rest might do the trick, but... -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Trond Myklebust on 25 May 2010 08:30 On Mon, 2010-05-24 at 23:24 +0200, Pavel Machek wrote: > Hi! > > > I encountered the following problem. We use short expiration time for > > kerberos contexts created by rpc.gssd (some patches were included in mainline > > nfs-utils). In particular, we use 120secs expiration time. > > > > Now, I run application that eats 80% of available RAM. Then I run 10 parallel > > dd processes that write data into NFS4 volume with sec=krb5. > > > > As soon as the kerberos context expires (i.e., up to 120 secs), the whole > > system gets stuck in do_page_fault and succesive functions. It is because > > there is no free memory in kernel, all free memory is used as cache for NFS4 > > (due to dd traffic), kernel ask NFS to write back its pages but NFS cannot do > > anything as it is missing valid context. NFS contacts rpc.gssd to provide > > a renewed context, the rpc.gssd does not provide the context as it needs some memory > > to scan /tmp for a ticket. I.e., it deadlocks. > > > > Longer context expiration time is no real solution as it only makes the > > deadlock less often. > > > > Any ideas what can be done here? (Please cc me.) We could preallocate some > > memory in rpc.gssd and use mlockall but not sure whether this proctects also > > kernel malloc for things related to rpc.gssd and context creation (new file > > descriptors and so on). > > > > This is seen in 2.6.32 kernel but most probably this is related to all kernel > > versions. > > Seems like pretty fundamental problem in nfs :-(. Limiting writeback > caches for nfs, so that system has enough memory to perform rpc calls > with the rest might do the trick, but... > It's the same problem that you have for any file or storage system that has initiators in userland. On the storage side, iSCSI in particular has the same problem. On the filesystem side, CIFS, AFS, coda, .... do too. The clustered filesystems can deadlock if the node that is running the DLM runs out of memory... A few years ago there were several people proposing various solutions for allowing these daemons to run in a protected memory environment to avoid deadlocks, but those efforts have since petered out. Perhaps it is time to review the problem? Cheers Trond -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Lukas Hejtmanek on 25 May 2010 09:00 Hi, On Tue, May 25, 2010 at 08:28:40AM -0400, Trond Myklebust wrote: > > Seems like pretty fundamental problem in nfs :-(. Limiting writeback > > caches for nfs, so that system has enough memory to perform rpc calls > > with the rest might do the trick, but... > > > > It's the same problem that you have for any file or storage system that > has initiators in userland. On the storage side, iSCSI in particular has > the same problem. On the filesystem side, CIFS, AFS, coda, .... do too. > The clustered filesystems can deadlock if the node that is running the > DLM runs out of memory... > > A few years ago there were several people proposing various solutions > for allowing these daemons to run in a protected memory environment to > avoid deadlocks, but those efforts have since petered out. Perhaps it is > time to review the problem? I saw some patches targeting 2.6.35 that should prevent some deadlocks. They seem to be not enough in some cases. rpc.* daemons should be mlocked for sure but there is a problem with libkrb that reads files using fread(). fread() uses anonymous mmap, under mlockall(MCL_FUTURE) this causes the anonymous map to be mapped instantly and it deadlocks. IBM GPFS also uses userspace daemon, but it seems that the deamon is mlocked and it does not open any files and does not create new connections. My problem was quite easily reproducible. I started an application that eats 80% of free memory. Then I started: for i in `seq 1 10`; do dd if=/dev/zero of=/mnt/nfs4/file$i bs=1M count=2048 & done it deadlock within 2 minutes until this patch is applied: commit 3d7b08945e54a3a5358d5890240619a013cb7388 Author: Trond Myklebust <Trond.Myklebust(a)netapp.com> Date: Thu Apr 22 15:35:55 2010 -0400 SUNRPC: Fix a bug in rpcauth_prune_expired Don't want to evict a credential if cred->cr_expire == jiffies, since that means that it was just placed on the cred_unused list. We therefore need to use time_in_range() rather than time_in_range_open(). Signed-off-by: Trond Myklebust <Trond.Myklebust(a)netapp.com> diff --git a/net/sunrpc/auth.c b/net/sunrpc/auth.c index f394fc1..95afe79 100644 --- a/net/sunrpc/auth.c +++ b/net/sunrpc/auth.c @@ -237,7 +237,7 @@ rpcauth_prune_expired(struct list_head *free, int nr_to_scan) list_for_each_entry_safe(cred, next, &cred_unused, cr_lru) { /* Enforce a 60 second garbage collection moratorium */ - if (time_in_range_open(cred->cr_expire, expired, jiffies) && + if (time_in_range(cred->cr_expire, expired, jiffies) && test_bit(RPCAUTH_CRED_HASHED, &cred->cr_flags) != 0) continue; but I believe this only hides the real problem. -- Luk� Hejtm�nek -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Trond Myklebust on 25 May 2010 09:40 On Tue, 2010-05-25 at 14:58 +0200, Lukas Hejtmanek wrote: > Hi, > > On Tue, May 25, 2010 at 08:28:40AM -0400, Trond Myklebust wrote: > > > Seems like pretty fundamental problem in nfs :-(. Limiting writeback > > > caches for nfs, so that system has enough memory to perform rpc calls > > > with the rest might do the trick, but... > > > > > > > It's the same problem that you have for any file or storage system that > > has initiators in userland. On the storage side, iSCSI in particular has > > the same problem. On the filesystem side, CIFS, AFS, coda, .... do too. > > The clustered filesystems can deadlock if the node that is running the > > DLM runs out of memory... > > > > A few years ago there were several people proposing various solutions > > for allowing these daemons to run in a protected memory environment to > > avoid deadlocks, but those efforts have since petered out. Perhaps it is > > time to review the problem? > > I saw some patches targeting 2.6.35 that should prevent some deadlocks. They > seem to be not enough in some cases. rpc.* daemons should be mlocked for sure > but there is a problem with libkrb that reads files using fread(). fread() uses > anonymous mmap, under mlockall(MCL_FUTURE) this causes the anonymous map to be > mapped instantly and it deadlocks. > > IBM GPFS also uses userspace daemon, but it seems that the deamon is mlocked > and it does not open any files and does not create new connections. Doesn't matter. Just writing to a socket or pipe may trigger a kernel memory allocation which can result in an attempt to reclaim memory. Furthermore, there is the issue of what to do when you really are OOM, and the kernel cannot allocate more memory for you without reclaiming it. The schemes I'm talking about typically had special memory pools preallocated for use by daemons, and would label the daemons using some equivalent of the PF_MEMALLOC flag to prevent recursion into the filesystem. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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