From: Tejun Heo Date: Wed, 28 Jul 2021 00:38:09 +0000 (-1000) Subject: blk-iocost: fix operation ordering in iocg_wake_fn() X-Git-Tag: v6.6-pxa1908~6007^2~1 X-Git-Url: https://git.dujemihanovic.xyz/?a=commitdiff_plain;h=5ab189cf3abbc9994bae3be524c5b88589ed56e2;p=linux.git blk-iocost: fix operation ordering in iocg_wake_fn() iocg_wake_fn() open-codes wait_queue_entry removal and wakeup because it wants the wq_entry to be always removed whether it ended up waking the task or not. finish_wait() tests whether wq_entry needs removal without grabbing the wait_queue lock and expects the waker to use list_del_init_careful() after all waking operations are complete, which iocg_wake_fn() didn't do. The operation order was wrong and the regular list_del_init() was used. The result is that if a waiter wakes up racing the waker, it can free pop the wq_entry off stack before the waker is still looking at it, which can lead to a backtrace like the following. [7312084.588951] general protection fault, probably for non-canonical address 0x586bf4005b2b88: 0000 [#1] SMP ... [7312084.647079] RIP: 0010:queued_spin_lock_slowpath+0x171/0x1b0 ... [7312084.858314] Call Trace: [7312084.863548] _raw_spin_lock_irqsave+0x22/0x30 [7312084.872605] try_to_wake_up+0x4c/0x4f0 [7312084.880444] iocg_wake_fn+0x71/0x80 [7312084.887763] __wake_up_common+0x71/0x140 [7312084.895951] iocg_kick_waitq+0xe8/0x2b0 [7312084.903964] ioc_rqos_throttle+0x275/0x650 [7312084.922423] __rq_qos_throttle+0x20/0x30 [7312084.930608] blk_mq_make_request+0x120/0x650 [7312084.939490] generic_make_request+0xca/0x310 [7312084.957600] submit_bio+0x173/0x200 [7312084.981806] swap_readpage+0x15c/0x240 [7312084.989646] read_swap_cache_async+0x58/0x60 [7312084.998527] swap_cluster_readahead+0x201/0x320 [7312085.023432] swapin_readahead+0x2df/0x450 [7312085.040672] do_swap_page+0x52f/0x820 [7312085.058259] handle_mm_fault+0xa16/0x1420 [7312085.066620] do_page_fault+0x2c6/0x5c0 [7312085.074459] page_fault+0x2f/0x40 Fix it by switching to list_del_init_careful() and putting it at the end. Signed-off-by: Tejun Heo Reported-by: Rik van Riel Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost") Cc: stable@vger.kernel.org # v5.4+ Signed-off-by: Jens Axboe --- diff --git a/block/blk-iocost.c b/block/blk-iocost.c index c2d6bc88d3f1..5fac3757e6e0 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -1440,16 +1440,17 @@ static int iocg_wake_fn(struct wait_queue_entry *wq_entry, unsigned mode, return -1; iocg_commit_bio(ctx->iocg, wait->bio, wait->abs_cost, cost); + wait->committed = true; /* * autoremove_wake_function() removes the wait entry only when it - * actually changed the task state. We want the wait always - * removed. Remove explicitly and use default_wake_function(). + * actually changed the task state. We want the wait always removed. + * Remove explicitly and use default_wake_function(). Note that the + * order of operations is important as finish_wait() tests whether + * @wq_entry is removed without grabbing the lock. */ - list_del_init(&wq_entry->entry); - wait->committed = true; - default_wake_function(wq_entry, mode, flags, key); + list_del_init_careful(&wq_entry->entry); return 0; }