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Diffstat (limited to '')
| -rw-r--r-- | debian/patches-rt/0150-locking-rt-mutex-fix-deadlock-in-device-mapper-block.patch | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/debian/patches-rt/0150-locking-rt-mutex-fix-deadlock-in-device-mapper-block.patch b/debian/patches-rt/0150-locking-rt-mutex-fix-deadlock-in-device-mapper-block.patch new file mode 100644 index 000000000..5404d73d6 --- /dev/null +++ b/debian/patches-rt/0150-locking-rt-mutex-fix-deadlock-in-device-mapper-block.patch @@ -0,0 +1,81 @@ +From d6b1373a76eff772848ccbfed73baf94c807e464 Mon Sep 17 00:00:00 2001 +From: Mikulas Patocka <mpatocka@redhat.com> +Date: Mon, 13 Nov 2017 12:56:53 -0500 +Subject: [PATCH 150/347] locking/rt-mutex: fix deadlock in device mapper / + block-IO +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.246-rt110.tar.xz + +When some block device driver creates a bio and submits it to another +block device driver, the bio is added to current->bio_list (in order to +avoid unbounded recursion). + +However, this queuing of bios can cause deadlocks, in order to avoid them, +device mapper registers a function flush_current_bio_list. This function +is called when device mapper driver blocks. It redirects bios queued on +current->bio_list to helper workqueues, so that these bios can proceed +even if the driver is blocked. + +The problem with CONFIG_PREEMPT_RT_FULL is that when the device mapper +driver blocks, it won't call flush_current_bio_list (because +tsk_is_pi_blocked returns true in sched_submit_work), so deadlocks in +block device stack can happen. + +Note that we can't call blk_schedule_flush_plug if tsk_is_pi_blocked +returns true - that would cause +BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in +task_blocks_on_rt_mutex when flush_current_bio_list attempts to take a +spinlock. + +So the proper fix is to call blk_schedule_flush_plug in rt_mutex_fastlock, +when fast acquire failed and when the task is about to block. + +CC: stable-rt@vger.kernel.org +[bigeasy: The deadlock is not device-mapper specific, it can also occur + in plain EXT4] +Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + kernel/locking/rtmutex.c | 13 +++++++++++++ + 1 file changed, 13 insertions(+) + +diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c +index cc47d5aa93a1..721e3a4916d9 100644 +--- a/kernel/locking/rtmutex.c ++++ b/kernel/locking/rtmutex.c +@@ -24,6 +24,7 @@ + #include <linux/sched/debug.h> + #include <linux/timer.h> + #include <linux/ww_mutex.h> ++#include <linux/blkdev.h> + + #include "rtmutex_common.h" + +@@ -1919,6 +1920,15 @@ rt_mutex_fastlock(struct rt_mutex *lock, int state, + if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) + return 0; + ++ /* ++ * If rt_mutex blocks, the function sched_submit_work will not call ++ * blk_schedule_flush_plug (because tsk_is_pi_blocked would be true). ++ * We must call blk_schedule_flush_plug here, if we don't call it, ++ * a deadlock in I/O may happen. ++ */ ++ if (unlikely(blk_needs_flush_plug(current))) ++ blk_schedule_flush_plug(current); ++ + return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK, ww_ctx); + } + +@@ -1936,6 +1946,9 @@ rt_mutex_timed_fastlock(struct rt_mutex *lock, int state, + likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) + return 0; + ++ if (unlikely(blk_needs_flush_plug(current))) ++ blk_schedule_flush_plug(current); ++ + return slowfn(lock, state, timeout, chwalk, ww_ctx); + } + +-- +2.36.1 + |