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authorTejun Heo <tj@kernel.org>2014-07-05 18:43:21 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-09-17 09:04:02 -0700
commitf5b48b7a3d0d1ab761ba939b6cbb4a07d37a750b (patch)
treeab084d309b39056007d2c94976a986b20fb9399d /block
parent6562c0cc805b391489e2f511983300e802864aea (diff)
downloadlinux-linaro-stable-f5b48b7a3d0d1ab761ba939b6cbb4a07d37a750b.tar.gz
blkcg: don't call into policy draining if root_blkg is already gone
commit 2a1b4cf2331d92bc009bf94fa02a24604cdaf24c upstream. 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 776687bce42b ("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: Tejun Heo <tj@kernel.org> Reported-by: Shirish Pargaonkar <spargaonkar@suse.com> Reported-by: Sasha Levin <sasha.levin@oracle.com> Reported-by: Jet Chen <jet.chen@intel.com> Tested-by: Shirish Pargaonkar <spargaonkar@suse.com> Signed-off-by: Jens Axboe <axboe@fb.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'block')
-rw-r--r--block/blk-cgroup.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index b95219d2168d..1ff8e97f853a 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -883,6 +883,13 @@ void blkcg_drain_queue(struct request_queue *q)
if (!q->root_blkg)
return;
+ /*
+ * @q could be exiting and already have destroyed all blkgs as
+ * indicated by NULL root_blkg. If so, don't confuse policies.
+ */
+ if (!q->root_blkg)
+ return;
+
blk_throtl_drain(q);
}