From 298359c5bf06c04258d7cf552426e198c47e83c1 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Tue, 23 Mar 2010 13:35:37 -0700 Subject: [PATCH] exit: fix oops in sync_mm_rss In 2.6.34-rc1, removing vhost_net module causes an oops in sync_mm_rss (called from do_exit) when workqueue is destroyed. This does not happen on net-next, or with vhost on top of to 2.6.33. The issue seems to be introduced by 34e55232e59f7b19050267a05ff1226e5cd122a5 ("mm: avoid false sharing of mm_counter) which added sync_mm_rss() that is passed task->mm, and dereferences it without checking. If task is a kernel thread, mm might be NULL. I think this might also happen e.g. with aio. This patch fixes the oops by calling sync_mm_rss when task->mm is set to NULL. I also added BUG_ON to detect any other cases where counters get incremented while mm is NULL. The oops I observed looks like this: BUG: unable to handle kernel NULL pointer dereference at 00000000000002a8 IP: [] sync_mm_rss+0x33/0x6f PGD 0 Oops: 0002 [#1] SMP last sysfs file: /sys/devices/system/cpu/cpu7/cache/index2/shared_cpu_map CPU 2 Modules linked in: vhost_net(-) tun bridge stp sunrpc ipv6 cpufreq_ondemand acpi_cpufreq freq_table kvm_intel kvm i5000_edac edac_core rtc_cmos bnx2 button i2c_i801 i2c_core rtc_core e1000e sg joydev ide_cd_mod serio_raw pcspkr rtc_lib cdrom virtio_net virtio_blk virtio_pci virtio_ring virtio af_packet e1000 shpchp aacraid uhci_hcd ohci_hcd ehci_hcd [last unloaded: microcode] Pid: 2046, comm: vhost Not tainted 2.6.34-rc1-vhost #25 System Planar/IBM System x3550 -[7978B3G]- RIP: 0010:[] [] sync_mm_rss+0x33/0x6f RSP: 0018:ffff8802379b7e60 EFLAGS: 00010202 RAX: 0000000000000008 RBX: ffff88023f2390c0 RCX: 0000000000000000 RDX: ffff88023f2396b0 RSI: 0000000000000000 RDI: ffff88023f2390c0 RBP: ffff8802379b7e60 R08: 0000000000000000 R09: 0000000000000000 R10: ffff88023aecfbc0 R11: 0000000000013240 R12: 0000000000000000 R13: ffffffff81051a6c R14: ffffe8ffffc0f540 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff880001e80000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 00000000000002a8 CR3: 000000023af23000 CR4: 00000000000406e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Process vhost (pid: 2046, threadinfo ffff8802379b6000, task ffff88023f2390c0) Stack: ffff8802379b7ee0 ffffffff81040687 ffffe8ffffc0f558 ffffffffa00a3e2d <0> 0000000000000000 ffff88023f2390c0 ffffffff81055817 ffff8802379b7e98 <0> ffff8802379b7e98 0000000100000286 ffff8802379b7ee0 ffff88023ad47d78 Call Trace: [] do_exit+0x147/0x6c4 [] ? handle_rx_net+0x0/0x17 [vhost_net] [] ? autoremove_wake_function+0x0/0x39 [] ? worker_thread+0x0/0x229 [] kthreadd+0x0/0xf2 [] kernel_thread_helper+0x4/0x10 [] ? kthread+0x0/0x87 [] ? kernel_thread_helper+0x0/0x10 Code: 00 8b 87 6c 02 00 00 85 c0 74 14 48 98 f0 48 01 86 a0 02 00 00 c7 87 6c 02 00 00 00 00 00 00 8b 87 70 02 00 00 85 c0 74 14 48 98 48 01 86 a8 02 00 00 c7 87 70 02 00 00 00 00 00 00 8b 87 74 RIP [] sync_mm_rss+0x33/0x6f RSP CR2: 00000000000002a8 ---[ end trace 41603ba922beddd2 ]--- Fixing recursive fault but reboot is needed! (note: handle_rx_net is a work item using workqueue in question). sync_mm_rss+0x33/0x6f gave me a hint. I also tried reverting 34e55232e59f7b19050267a05ff1226e5cd122a5 and the oops goes away. The module in question calls use_mm and later unuse_mm from a kernel thread. It is when this kernel thread is destroyed that the crash happens. Signed-off-by: Michael S. Tsirkin Andrea Arcangeli Reviewed-by: Rik van Riel Reviewed-by: KAMEZAWA Hiroyuki Reviewed-by: Minchan Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memory.c | 1 + mm/mmu_context.c | 1 + 2 files changed, 2 insertions(+) diff --git a/mm/memory.c b/mm/memory.c index 5b7f200..bc9ba5a 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -130,6 +130,7 @@ void __sync_task_rss_stat(struct task_struct *task, struct mm_struct *mm) for (i = 0; i < NR_MM_COUNTERS; i++) { if (task->rss_stat.count[i]) { + BUG_ON(!mm); add_mm_counter(mm, i, task->rss_stat.count[i]); task->rss_stat.count[i] = 0; } diff --git a/mm/mmu_context.c b/mm/mmu_context.c index 0777654..9e82e93 100644 --- a/mm/mmu_context.c +++ b/mm/mmu_context.c @@ -53,6 +53,7 @@ void unuse_mm(struct mm_struct *mm) struct task_struct *tsk = current; task_lock(tsk); + sync_mm_rss(tsk, mm); tsk->mm = NULL; /* active_mm is still 'mm' */ enter_lazy_tlb(mm, tsk); -- 2.7.4