• Michael S. Tsirkin's avatar
    exit: fix oops in sync_mm_rss · 298359c5
    Michael S. Tsirkin authored
    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
    34e55232 ("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: [<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)
     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
    34e55232 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
    Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
    Andrea Arcangeli <aarcange@redhat.com>
    Reviewed-by: default avatarRik van Riel <riel@redhat.com>
    Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Reviewed-by: default avatarMinchan Kim <minchan.kim@gmail.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
mmu_context.c 1.36 KB