• Tejun Heo's avatar
    blkcg: don't call into policy draining if root_blkg is already gone · 0b462c89
    Tejun Heo authored
    While a queue is being destroyed, all the blkgs are destroyed and its
    ->root_blkg pointer is set to NULL.  If someone else starts to drain
    while the queue is in this state, the following oops happens.
    
      NULL pointer dereference at 0000000000000028
      IP: [<ffffffff8144e944>] blk_throtl_drain+0x84/0x230
      PGD e4a1067 PUD b773067 PMD 0
      Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
      Modules linked in: cfq_iosched(-) [last unloaded: cfq_iosched]
      CPU: 1 PID: 537 Comm: bash Not tainted 3.16.0-rc3-work+ #2
      Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
      task: ffff88000e222250 ti: ffff88000efd4000 task.ti: ffff88000efd4000
      RIP: 0010:[<ffffffff8144e944>]  [<ffffffff8144e944>] blk_throtl_drain+0x84/0x230
      RSP: 0018:ffff88000efd7bf0  EFLAGS: 00010046
      RAX: 0000000000000000 RBX: ffff880015091450 RCX: 0000000000000001
      RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
      RBP: ffff88000efd7c10 R08: 0000000000000000 R09: 0000000000000001
      R10: ffff88000e222250 R11: 0000000000000000 R12: ffff880015091450
      R13: ffff880015092e00 R14: ffff880015091d70 R15: ffff88001508fc28
      FS:  00007f1332650740(0000) GS:ffff88001fa80000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
      CR2: 0000000000000028 CR3: 0000000009446000 CR4: 00000000000006e0
      Stack:
       ffffffff8144e8f6 ffff880015091450 0000000000000000 ffff880015091d80
       ffff88000efd7c28 ffffffff8144ae2f ffff880015091450 ffff88000efd7c58
       ffffffff81427641 ffff880015091450 ffffffff82401f00 ffff880015091450
      Call Trace:
       [<ffffffff8144ae2f>] blkcg_drain_queue+0x1f/0x60
       [<ffffffff81427641>] __blk_drain_queue+0x71/0x180
       [<ffffffff81429b3e>] blk_queue_bypass_start+0x6e/0xb0
       [<ffffffff814498b8>] blkcg_deactivate_policy+0x38/0x120
       [<ffffffff8144ec44>] blk_throtl_exit+0x34/0x50
       [<ffffffff8144aea5>] blkcg_exit_queue+0x35/0x40
       [<ffffffff8142d476>] blk_release_queue+0x26/0xd0
       [<ffffffff81454968>] kobject_cleanup+0x38/0x70
       [<ffffffff81454848>] kobject_put+0x28/0x60
       [<ffffffff81427505>] blk_put_queue+0x15/0x20
       [<ffffffff817d07bb>] scsi_device_dev_release_usercontext+0x16b/0x1c0
       [<ffffffff810bc339>] execute_in_process_context+0x89/0xa0
       [<ffffffff817d064c>] scsi_device_dev_release+0x1c/0x20
       [<ffffffff817930e2>] device_release+0x32/0xa0
       [<ffffffff81454968>] kobject_cleanup+0x38/0x70
       [<ffffffff81454848>] kobject_put+0x28/0x60
       [<ffffffff817934d7>] put_device+0x17/0x20
       [<ffffffff817d11b9>] __scsi_remove_device+0xa9/0xe0
       [<ffffffff817d121b>] scsi_remove_device+0x2b/0x40
       [<ffffffff817d1257>] sdev_store_delete+0x27/0x30
       [<ffffffff81792ca8>] dev_attr_store+0x18/0x30
       [<ffffffff8126f75e>] sysfs_kf_write+0x3e/0x50
       [<ffffffff8126ea87>] kernfs_fop_write+0xe7/0x170
       [<ffffffff811f5e9f>] vfs_write+0xaf/0x1d0
       [<ffffffff811f69bd>] SyS_write+0x4d/0xc0
       [<ffffffff81d24692>] system_call_fastpath+0x16/0x1b
    
    776687bc ("block, blk-mq: draining can't be skipped even if
    bypass_depth was non-zero") made it easier to trigger this bug by
    making blk_queue_bypass_start() drain even when it loses the first
    bypass test to blk_cleanup_queue(); however, the bug has always been
    there even before the commit as blk_queue_bypass_start() could race
    against queue destruction, win the initial bypass test but perform the
    actual draining after blk_cleanup_queue() already destroyed all blkgs.
    
    Fix it by skippping calling into policy draining if all the blkgs are
    already gone.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Reported-by: default avatarShirish Pargaonkar <spargaonkar@suse.com>
    Reported-by: default avatarSasha Levin <sasha.levin@oracle.com>
    Reported-by: default avatarJet Chen <jet.chen@intel.com>
    Cc: stable@vger.kernel.org
    Tested-by: default avatarShirish Pargaonkar <spargaonkar@suse.com>
    Signed-off-by: default avatarJens Axboe <axboe@fb.com>
    0b462c89
blk-cgroup.c 29.5 KB