On Tue, 16 Mar 2010 19:08:08 +0200 "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > 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: that commit added function > 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: [<ffffffff810b436d>] 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:[<ffffffff810b436d>] [<ffffffff810b436d>] 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: > [<ffffffff81040687>] do_exit+0x147/0x6c4 > [<ffffffffa00a3e2d>] ? handle_rx_net+0x0/0x17 [vhost_net] > [<ffffffff81055817>] ? autoremove_wake_function+0x0/0x39 > [<ffffffff81051a6c>] ? worker_thread+0x0/0x229 > [<ffffffff810553c9>] kthreadd+0x0/0xf2 > [<ffffffff810038d4>] kernel_thread_helper+0x4/0x10 > [<ffffffff81055342>] ? kthread+0x0/0x87 > [<ffffffff810038d0>] ? 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 <f0> 48 01 86 a8 02 00 00 c7 87 70 02 00 00 00 00 00 00 8b 87 74 > RIP [<ffffffff810b436d>] sync_mm_rss+0x33/0x6f > RSP <ffff8802379b7e60> > 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 <mst@xxxxxxxxxx> Thank you very much. Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > --- > mm/memory.c | 1 + > mm/mmu_context.c | 1 + > 2 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index d1153e3..27022b3 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); > -- > 1.7.0.18.g0d53a5 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>