mm: gpf in global_dirty_limits

[Sasha Levin]

Hi all,

While fuzzing with trinity inside a KVM tools guest running the latest -next
kernel I've stumbled on the following spew:

[ 1139.410483] general protection fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[ 1139.413202] Dumping ftrace buffer:
[ 1139.414152]    (ftrace buffer empty)
[ 1139.415069] Modules linked in:
[ 1139.415846] CPU: 10 PID: 39777 Comm: kworker/u115:2 Tainted: G        W     3.15.0-rc4-next-20140506-sasha-00021-gc164334-dirty #447
[ 1139.418931] Workqueue: writeback bdi_writeback_workfn (flush-7:10)
[ 1139.420320] task: ffff880285848000 ti: ffff880282dbc000 task.ti: ffff880282dbc000
[ 1139.420320] RIP: global_dirty_limits (include/trace/events/writeback.h:308 mm/page-writeback.c:309)
[ 1139.420320] RSP: 0018:ffff880282dbdc28  EFLAGS: 00010282
[ 1139.420320] RAX: 6b6b6b6b6b6b6b6b RBX: 0000000000088034 RCX: 0000000000000001
[ 1139.420320] RDX: 0000000000110068 RSI: 0000000000088034 RDI: 6b6b6b6b6b6b6b6b
[ 1139.420320] RBP: ffff880282dbdc48 R08: 00000000000abad6 R09: ffff880285848cf0
[ 1139.420320] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000110068
[ 1139.420320] R13: ffff8805bc5932a8 R14: ffff880282dbdc60 R15: 0000000000001cc0
[ 1139.420320] FS:  0000000000000000(0000) GS:ffff880292c00000(0000) knlGS:0000000000000000
[ 1139.420320] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 1139.420320] CR2: 0000000000000001 CR3: 0000000025e2d000 CR4: 00000000000006a0
[ 1139.438692] Stack:
[ 1139.438692]  ffff8804e3ed0278 ffff8804e3ed0570 0000000000000000 ffff8804e3ed06c8
[ 1139.438692]  ffff880282dbdc78 ffffffffa1342180 0000000000088034 0000000000110068
[ 1139.438692]  0000000000000000 ffff8804e3ed0570 ffff880282dbdd38 ffffffffa1346f3a
[ 1139.438692] Call Trace:
[ 1139.438692] over_bground_thresh (arch/x86/include/asm/atomic64_64.h:21 include/asm-generic/atomic-long.h:31 include/linux/vmstat.h:122 fs/fs-writeback.c:772)
[ 1139.438692] bdi_writeback_workfn (fs/fs-writeback.c:934 fs/fs-writeback.c:1014 fs/fs-writeback.c:1043)
[ 1139.438692] process_one_work (kernel/workqueue.c:2227 include/linux/jump_label.h:105 include/trace/events/workqueue.h:111 kernel/workqueue.c:2232)
[ 1139.438692] ? process_one_work (include/linux/workqueue.h:186 kernel/workqueue.c:611 kernel/workqueue.c:638 kernel/workqueue.c:2220)
[ 1139.438692] worker_thread (kernel/workqueue.c:2354)
[ 1139.438692] ? rescuer_thread (kernel/workqueue.c:2303)
[ 1139.438692] kthread (kernel/kthread.c:210)
[ 1139.438692] ? kthread_create_on_node (kernel/kthread.c:176)
[ 1139.438692] ret_from_fork (arch/x86/kernel/entry_64.S:553)
[ 1139.438692] ? kthread_create_on_node (kernel/kthread.c:176)
[ 1139.438692] Code: 25 a0 da 00 00 0f 84 82 00 00 00 66 90 eb 2e 66 0f 1f 44 00 00 49 8b 45 00 0f 1f 40 00 49 8b 7d 08 4c 89 e2 49 83 c5 10 48 89 de <ff> d0 49 8b 45 00 48 85 c0 75 e7 eb c5 0f 1f 44 00 00 eb 53 66
[ 1139.438692] RIP global_dirty_limits (include/trace/events/writeback.h:308 mm/page-writeback.c:309)
[ 1139.438692]  RSP <ffff880282dbdc28>


Thanks,
Sasha
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