kernel/drivers/md/dm-delay.c, branch linux-6.9.y

dm-delay: fix max_delay calculations

2024-05-30T07:44:35Z

[ Upstream commit 64eb88d6caee2c8eb806a68dab3f184f14f818a4 ] delay_ctr() pointlessly compared max_delay in cases where multiple delay classes were initialized identically. Also, when write delays were configured different than read delays, delay_ctr() never compared their value against max_delay. Fix these issues. Fixes: 70bbeb29fab0 ("dm delay: for short delays, use kthread instead of timers and wq") Signed-off-by: Benjamin Marzinski Signed-off-by: Mike Snitzer Signed-off-by: Sasha Levin

dm-delay: fix hung task introduced by kthread mode

2024-05-30T07:44:35Z

[ Upstream commit d14646f23300a5fc85be867bafdc0702c2002789 ] If the worker thread is not woken due to a bio, then it is not woken at all. This causes the hung task check to trigger. This occurs, for instance, when no bios are submitted. Also when a delay of 0 is configured, delay_bio() returns without waking the worker. Prevent the hung task check from triggering by creating the thread with kthread_run() instead of using kthread_create() directly. Fixes: 70bbeb29fab0 ("dm delay: for short delays, use kthread instead of timers and wq") Signed-off-by: Joel Colledge Reviewed-by: Benjamin Marzinski Signed-off-by: Mike Snitzer Signed-off-by: Sasha Levin

dm-delay: fix workqueue delay_timer race

2024-05-30T07:44:35Z

[ Upstream commit 8d24790ed08ab4e619ce58ed4a1b353ab77ffdc5 ] delay_timer could be pending when delay_dtr() is called. It needs to be shut down before kdelayd_wq is destroyed, so it won't try queueing more work to kdelayd_wq while that's getting destroyed. Also the del_timer_sync() call in delay_presuspend() doesn't protect against the timer getting immediately rearmed by the queued call to flush_delayed_bios(), but there's no real harm if that does happen. timer_delete() is less work, and is basically just as likely to stop a pointless call to flush_delayed_bios(). Fixes: 26b9f228703f ("dm: delay target") Signed-off-by: Benjamin Marzinski Signed-off-by: Mike Snitzer Signed-off-by: Sasha Levin

dm-delay: avoid duplicate logic

2023-11-17T19:41:14Z

This is small refactoring of dm-delay - we avoid duplicate logic in flush_delayed_bios and flush_delayed_bios_fast and join these two functions into one. We also add cond_resched() to flush_delayed_bios because the list may have unbounded number of entries. Signed-off-by: Mikulas Patocka Signed-off-by: Mike Snitzer

dm-delay: fix bugs introduced by kthread mode

2023-11-17T19:41:14Z

This commit fixes the following bugs introduced by commit 70bbeb29fab0 ("dm delay: for short delays, use kthread instead of timers and wq"): * the function flush_worker_fn has no exit path - on unload, this function will just loop and consume 100% CPU without any progress * the wake-up mechanism in flush_worker_fn is racy - a wake up will be missed if the process adds entries to the delayed_bios list just before set_current_state(TASK_INTERRUPTIBLE) * flush_delayed_bios_fast submits a bio while holding a global mutex; this may deadlock if we have multiple stacked dm-delay devices and the underlying device attempts to acquire the mutex too * if the target constructor fails, it will call delay_dtr. delay_dtr would attempt to free dc->timer_lock without it being initialized by the constructor. * if the target constructor's kthread allocation fails, delay_dtr would crash trying to dereference dc->worker because it is non-NULL due to ERR_PTR. Fixes: 70bbeb29fab0 ("dm delay: for short delays, use kthread instead of timers and wq") Signed-off-by: Mikulas Patocka Signed-off-by: Mike Snitzer

dm-delay: fix a race between delay_presuspend and delay_bio

2023-11-17T19:38:46Z

In delay_presuspend, we set the atomic variable may_delay and then stop the timer and flush pending bios. The intention here is to prevent the delay target from re-arming the timer again. However, this test is racy. Suppose that one thread goes to delay_bio, sees that dc->may_delay is one and proceeds; now, another thread executes delay_presuspend, it sets dc->may_delay to zero, deletes the timer and flushes pending bios. Then, the first thread continues and adds the bio to delayed->list despite the fact that dc->may_delay is false. Fix this bug by changing may_delay's type from atomic_t to bool and only access it while holding the delayed_bios_lock mutex. Note that we don't have to grab the mutex in delay_resume because there are no bios in flight at this point. Signed-off-by: Mikulas Patocka Cc: stable@vger.kernel.org Signed-off-by: Mike Snitzer

dm delay: for short delays, use kthread instead of timers and wq

2023-10-31T15:06:21Z

DM delay's current design of using timers and wq to realize the delays is insufficient for delays below ~50ms. This commit enhances the design to use a kthread to flush the expired delays, trading some CPU time (in some cases) for better delay accuracy and delays closer to what the user requested for smaller delays. The new design is chosen as long as all the delays are below 50ms. Since bios can't be completed in interrupt context using a kthread is probably the most reasonable way to approach this. Testing with echo "0 2097152 zero" | dmsetup create dm-zeros for i in $(seq 0 20); do echo "0 2097152 delay /dev/mapper/dm-zeros 0 $i" | dmsetup create dm-delay-${i}ms; done Some performance numbers for comparison, on beaglebone black (single core) CONFIG_HZ_1000=y: fio --name=1msread --rw=randread --bs=4k --runtime=60 --time_based \ --filename=/dev/mapper/dm-delay-1ms Theoretical maximum: 1000 IOPS Previous: 250 IOPS Kthread: 500 IOPS fio --name=10msread --rw=randread --bs=4k --runtime=60 --time_based \ --filename=/dev/mapper/dm-delay-10ms Theoretical maximum: 100 IOPS Previous: 45 IOPS Kthread: 50 IOPS fio --name=1mswrite --rw=randwrite --direct=1 --bs=4k --runtime=60 \ --time_based --filename=/dev/mapper/dm-delay-1ms Theoretical maximum: 1000 IOPS Previous: 498 IOPS Kthread: 1000 IOPS fio --name=10mswrite --rw=randwrite --direct=1 --bs=4k --runtime=60 \ --time_based --filename=/dev/mapper/dm-delay-10ms Theoretical maximum: 100 IOPS Previous: 90 IOPS Kthread: 100 IOPS (This one is just to prove the new design isn't impacting throughput, not really about delays): fio --name=10mswriteasync --rw=randwrite --direct=1 --bs=4k \ --runtime=60 --time_based --filename=/dev/mapper/dm-delay-10ms \ --numjobs=32 --iodepth=64 --ioengine=libaio --group_reporting Previous: 13.3k IOPS Kthread: 13.3k IOPS Signed-off-by: Christian Loehle [Harshit: kthread_create error handling fix in delay_ctr] Signed-off-by: Harshit Mogalapalli Signed-off-by: Mike Snitzer

dm: add helper macro for simple DM target module init and exit

2023-04-11T16:09:08Z

Eliminate duplicate boilerplate code for simple modules that contain a single DM target driver without any additional setup code. Add a new module_dm() macro, which replaces the module_init() and module_exit() with template functions that call dm_register_target() and dm_unregister_target() respectively. Signed-off-by: Yangtao Li Signed-off-by: Mike Snitzer

dm: push error reporting down to dm_register_target()

2023-04-11T16:01:01Z

Simplifies each DM target's init method by making dm_register_target() responsible for its error reporting (on behalf of targets). Signed-off-by: Yangtao Li Signed-off-by: Mike Snitzer

dm: change "unsigned" to "unsigned int"

2023-02-14T19:23:06Z

Signed-off-by: Heinz Mauelshagen Signed-off-by: Mike Snitzer