* Re: Patch "dm delay: for short delays, use kthread instead of timers and wq" has been added to the 6.6-stable tree [not found] <20231129025441.892320-1-sashal@kernel.org> @ 2023-11-29 8:28 ` Mikulas Patocka 2023-11-29 10:02 ` Christian Loehle 0 siblings, 1 reply; 8+ messages in thread From: Mikulas Patocka @ 2023-11-29 8:28 UTC (permalink / raw) To: Sasha Levin Cc: stable-commits, stable, christian.loehle, Alasdair Kergon, Mike Snitzer, dm-devel Hi This patch doesn't fix any bug (and introduces several serious bugs), so it shouldn't be backported at all. Mikulas On Tue, 28 Nov 2023, Sasha Levin wrote: > This is a note to let you know that I've just added the patch titled > > dm delay: for short delays, use kthread instead of timers and wq > > to the 6.6-stable tree which can be found at: > http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary > > The filename of the patch is: > dm-delay-for-short-delays-use-kthread-instead-of-tim.patch > and it can be found in the queue-6.6 subdirectory. > > If you, or anyone else, feels it should not be added to the stable tree, > please let <stable@vger.kernel.org> know about it. > > > > commit 976fd593415e170a8ed5db68683b280d5876982d > Author: Christian Loehle <christian.loehle@arm.com> > Date: Fri Oct 20 12:46:05 2023 +0100 > > dm delay: for short delays, use kthread instead of timers and wq > > [ Upstream commit 70bbeb29fab09d6ea6cfe64109db60a97d84d739 ] > > 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 <christian.loehle@arm.com> > [Harshit: kthread_create error handling fix in delay_ctr] > Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com> > Signed-off-by: Mike Snitzer <snitzer@kernel.org> > Stable-dep-of: 6fc45b6ed921 ("dm-delay: fix a race between delay_presuspend and delay_bio") > Signed-off-by: Sasha Levin <sashal@kernel.org> > > diff --git a/drivers/md/dm-delay.c b/drivers/md/dm-delay.c > index 7433525e59856..efd510984e259 100644 > --- a/drivers/md/dm-delay.c > +++ b/drivers/md/dm-delay.c > @@ -13,6 +13,7 @@ > #include <linux/blkdev.h> > #include <linux/bio.h> > #include <linux/slab.h> > +#include <linux/kthread.h> > > #include <linux/device-mapper.h> > > @@ -31,6 +32,7 @@ struct delay_c { > struct workqueue_struct *kdelayd_wq; > struct work_struct flush_expired_bios; > struct list_head delayed_bios; > + struct task_struct *worker; > atomic_t may_delay; > > struct delay_class read; > @@ -66,6 +68,44 @@ static void queue_timeout(struct delay_c *dc, unsigned long expires) > mutex_unlock(&dc->timer_lock); > } > > +static inline bool delay_is_fast(struct delay_c *dc) > +{ > + return !!dc->worker; > +} > + > +static void flush_delayed_bios_fast(struct delay_c *dc, bool flush_all) > +{ > + struct dm_delay_info *delayed, *next; > + > + mutex_lock(&delayed_bios_lock); > + list_for_each_entry_safe(delayed, next, &dc->delayed_bios, list) { > + if (flush_all || time_after_eq(jiffies, delayed->expires)) { > + struct bio *bio = dm_bio_from_per_bio_data(delayed, > + sizeof(struct dm_delay_info)); > + list_del(&delayed->list); > + dm_submit_bio_remap(bio, NULL); > + delayed->class->ops--; > + } > + } > + mutex_unlock(&delayed_bios_lock); > +} > + > +static int flush_worker_fn(void *data) > +{ > + struct delay_c *dc = data; > + > + while (1) { > + flush_delayed_bios_fast(dc, false); > + if (unlikely(list_empty(&dc->delayed_bios))) { > + set_current_state(TASK_INTERRUPTIBLE); > + schedule(); > + } else > + cond_resched(); > + } > + > + return 0; > +} > + > static void flush_bios(struct bio *bio) > { > struct bio *n; > @@ -78,7 +118,7 @@ static void flush_bios(struct bio *bio) > } > } > > -static struct bio *flush_delayed_bios(struct delay_c *dc, int flush_all) > +static struct bio *flush_delayed_bios(struct delay_c *dc, bool flush_all) > { > struct dm_delay_info *delayed, *next; > unsigned long next_expires = 0; > @@ -115,7 +155,10 @@ static void flush_expired_bios(struct work_struct *work) > struct delay_c *dc; > > dc = container_of(work, struct delay_c, flush_expired_bios); > - flush_bios(flush_delayed_bios(dc, 0)); > + if (delay_is_fast(dc)) > + flush_delayed_bios_fast(dc, false); > + else > + flush_bios(flush_delayed_bios(dc, false)); > } > > static void delay_dtr(struct dm_target *ti) > @@ -131,8 +174,11 @@ static void delay_dtr(struct dm_target *ti) > dm_put_device(ti, dc->write.dev); > if (dc->flush.dev) > dm_put_device(ti, dc->flush.dev); > + if (dc->worker) > + kthread_stop(dc->worker); > > - mutex_destroy(&dc->timer_lock); > + if (!delay_is_fast(dc)) > + mutex_destroy(&dc->timer_lock); > > kfree(dc); > } > @@ -175,6 +221,7 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) > { > struct delay_c *dc; > int ret; > + unsigned int max_delay; > > if (argc != 3 && argc != 6 && argc != 9) { > ti->error = "Requires exactly 3, 6 or 9 arguments"; > @@ -188,16 +235,14 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) > } > > ti->private = dc; > - timer_setup(&dc->delay_timer, handle_delayed_timer, 0); > - INIT_WORK(&dc->flush_expired_bios, flush_expired_bios); > INIT_LIST_HEAD(&dc->delayed_bios); > - mutex_init(&dc->timer_lock); > atomic_set(&dc->may_delay, 1); > dc->argc = argc; > > ret = delay_class_ctr(ti, &dc->read, argv); > if (ret) > goto bad; > + max_delay = dc->read.delay; > > if (argc == 3) { > ret = delay_class_ctr(ti, &dc->write, argv); > @@ -206,6 +251,8 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) > ret = delay_class_ctr(ti, &dc->flush, argv); > if (ret) > goto bad; > + max_delay = max(max_delay, dc->write.delay); > + max_delay = max(max_delay, dc->flush.delay); > goto out; > } > > @@ -216,19 +263,37 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) > ret = delay_class_ctr(ti, &dc->flush, argv + 3); > if (ret) > goto bad; > + max_delay = max(max_delay, dc->flush.delay); > goto out; > } > > ret = delay_class_ctr(ti, &dc->flush, argv + 6); > if (ret) > goto bad; > + max_delay = max(max_delay, dc->flush.delay); > > out: > - dc->kdelayd_wq = alloc_workqueue("kdelayd", WQ_MEM_RECLAIM, 0); > - if (!dc->kdelayd_wq) { > - ret = -EINVAL; > - DMERR("Couldn't start kdelayd"); > - goto bad; > + if (max_delay < 50) { > + /* > + * In case of small requested delays, use kthread instead of > + * timers and workqueue to achieve better latency. > + */ > + dc->worker = kthread_create(&flush_worker_fn, dc, > + "dm-delay-flush-worker"); > + if (IS_ERR(dc->worker)) { > + ret = PTR_ERR(dc->worker); > + goto bad; > + } > + } else { > + timer_setup(&dc->delay_timer, handle_delayed_timer, 0); > + INIT_WORK(&dc->flush_expired_bios, flush_expired_bios); > + mutex_init(&dc->timer_lock); > + dc->kdelayd_wq = alloc_workqueue("kdelayd", WQ_MEM_RECLAIM, 0); > + if (!dc->kdelayd_wq) { > + ret = -EINVAL; > + DMERR("Couldn't start kdelayd"); > + goto bad; > + } > } > > ti->num_flush_bios = 1; > @@ -260,7 +325,10 @@ static int delay_bio(struct delay_c *dc, struct delay_class *c, struct bio *bio) > list_add_tail(&delayed->list, &dc->delayed_bios); > mutex_unlock(&delayed_bios_lock); > > - queue_timeout(dc, expires); > + if (delay_is_fast(dc)) > + wake_up_process(dc->worker); > + else > + queue_timeout(dc, expires); > > return DM_MAPIO_SUBMITTED; > } > @@ -270,8 +338,13 @@ static void delay_presuspend(struct dm_target *ti) > struct delay_c *dc = ti->private; > > atomic_set(&dc->may_delay, 0); > - del_timer_sync(&dc->delay_timer); > - flush_bios(flush_delayed_bios(dc, 1)); > + > + if (delay_is_fast(dc)) > + flush_delayed_bios_fast(dc, true); > + else { > + del_timer_sync(&dc->delay_timer); > + flush_bios(flush_delayed_bios(dc, true)); > + } > } > > static void delay_resume(struct dm_target *ti) > @@ -356,7 +429,7 @@ static int delay_iterate_devices(struct dm_target *ti, > > static struct target_type delay_target = { > .name = "delay", > - .version = {1, 3, 0}, > + .version = {1, 4, 0}, > .features = DM_TARGET_PASSES_INTEGRITY, > .module = THIS_MODULE, > .ctr = delay_ctr, > ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Patch "dm delay: for short delays, use kthread instead of timers and wq" has been added to the 6.6-stable tree 2023-11-29 8:28 ` Patch "dm delay: for short delays, use kthread instead of timers and wq" has been added to the 6.6-stable tree Mikulas Patocka @ 2023-11-29 10:02 ` Christian Loehle 2023-11-29 17:28 ` Mikulas Patocka 0 siblings, 1 reply; 8+ messages in thread From: Christian Loehle @ 2023-11-29 10:02 UTC (permalink / raw) To: Mikulas Patocka, Sasha Levin Cc: stable-commits, stable, Alasdair Kergon, Mike Snitzer, dm-devel Hi Mikulas, Agreed and thanks for fixing. Has this been selected for stable because of: 6fc45b6ed921 ("dm-delay: fix a race between delay_presuspend and delay_bio") If so, I would volunteer do the backports for that for you at least. BR, Christian On 29/11/2023 08:28, Mikulas Patocka wrote: > Hi > > This patch doesn't fix any bug (and introduces several serious bugs), so > it shouldn't be backported at all. > > Mikulas > > > On Tue, 28 Nov 2023, Sasha Levin wrote: > >> This is a note to let you know that I've just added the patch titled >> >> dm delay: for short delays, use kthread instead of timers and wq >> >> to the 6.6-stable tree which can be found at: >> http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary >> >> The filename of the patch is: >> dm-delay-for-short-delays-use-kthread-instead-of-tim.patch >> and it can be found in the queue-6.6 subdirectory. >> >> If you, or anyone else, feels it should not be added to the stable tree, >> please let <stable@vger.kernel.org> know about it. >> >> >> >> commit 976fd593415e170a8ed5db68683b280d5876982d >> Author: Christian Loehle <christian.loehle@arm.com> >> Date: Fri Oct 20 12:46:05 2023 +0100 >> >> dm delay: for short delays, use kthread instead of timers and wq >> >> [ Upstream commit 70bbeb29fab09d6ea6cfe64109db60a97d84d739 ] >> >> 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 <christian.loehle@arm.com> >> [Harshit: kthread_create error handling fix in delay_ctr] >> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com> >> Signed-off-by: Mike Snitzer <snitzer@kernel.org> >> Stable-dep-of: 6fc45b6ed921 ("dm-delay: fix a race between delay_presuspend and delay_bio") >> Signed-off-by: Sasha Levin <sashal@kernel.org> >> >> diff --git a/drivers/md/dm-delay.c b/drivers/md/dm-delay.c >> index 7433525e59856..efd510984e259 100644 >> --- a/drivers/md/dm-delay.c >> +++ b/drivers/md/dm-delay.c >> @@ -13,6 +13,7 @@ >> #include <linux/blkdev.h> >> #include <linux/bio.h> >> #include <linux/slab.h> >> +#include <linux/kthread.h> >> >> #include <linux/device-mapper.h> >> >> @@ -31,6 +32,7 @@ struct delay_c { >> struct workqueue_struct *kdelayd_wq; >> struct work_struct flush_expired_bios; >> struct list_head delayed_bios; >> + struct task_struct *worker; >> atomic_t may_delay; >> >> struct delay_class read; >> @@ -66,6 +68,44 @@ static void queue_timeout(struct delay_c *dc, unsigned long expires) >> mutex_unlock(&dc->timer_lock); >> } >> >> +static inline bool delay_is_fast(struct delay_c *dc) >> +{ >> + return !!dc->worker; >> +} >> + >> +static void flush_delayed_bios_fast(struct delay_c *dc, bool flush_all) >> +{ >> + struct dm_delay_info *delayed, *next; >> + >> + mutex_lock(&delayed_bios_lock); >> + list_for_each_entry_safe(delayed, next, &dc->delayed_bios, list) { >> + if (flush_all || time_after_eq(jiffies, delayed->expires)) { >> + struct bio *bio = dm_bio_from_per_bio_data(delayed, >> + sizeof(struct dm_delay_info)); >> + list_del(&delayed->list); >> + dm_submit_bio_remap(bio, NULL); >> + delayed->class->ops--; >> + } >> + } >> + mutex_unlock(&delayed_bios_lock); >> +} >> + >> +static int flush_worker_fn(void *data) >> +{ >> + struct delay_c *dc = data; >> + >> + while (1) { >> + flush_delayed_bios_fast(dc, false); >> + if (unlikely(list_empty(&dc->delayed_bios))) { >> + set_current_state(TASK_INTERRUPTIBLE); >> + schedule(); >> + } else >> + cond_resched(); >> + } >> + >> + return 0; >> +} >> + >> static void flush_bios(struct bio *bio) >> { >> struct bio *n; >> @@ -78,7 +118,7 @@ static void flush_bios(struct bio *bio) >> } >> } >> >> -static struct bio *flush_delayed_bios(struct delay_c *dc, int flush_all) >> +static struct bio *flush_delayed_bios(struct delay_c *dc, bool flush_all) >> { >> struct dm_delay_info *delayed, *next; >> unsigned long next_expires = 0; >> @@ -115,7 +155,10 @@ static void flush_expired_bios(struct work_struct *work) >> struct delay_c *dc; >> >> dc = container_of(work, struct delay_c, flush_expired_bios); >> - flush_bios(flush_delayed_bios(dc, 0)); >> + if (delay_is_fast(dc)) >> + flush_delayed_bios_fast(dc, false); >> + else >> + flush_bios(flush_delayed_bios(dc, false)); >> } >> >> static void delay_dtr(struct dm_target *ti) >> @@ -131,8 +174,11 @@ static void delay_dtr(struct dm_target *ti) >> dm_put_device(ti, dc->write.dev); >> if (dc->flush.dev) >> dm_put_device(ti, dc->flush.dev); >> + if (dc->worker) >> + kthread_stop(dc->worker); >> >> - mutex_destroy(&dc->timer_lock); >> + if (!delay_is_fast(dc)) >> + mutex_destroy(&dc->timer_lock); >> >> kfree(dc); >> } >> @@ -175,6 +221,7 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) >> { >> struct delay_c *dc; >> int ret; >> + unsigned int max_delay; >> >> if (argc != 3 && argc != 6 && argc != 9) { >> ti->error = "Requires exactly 3, 6 or 9 arguments"; >> @@ -188,16 +235,14 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) >> } >> >> ti->private = dc; >> - timer_setup(&dc->delay_timer, handle_delayed_timer, 0); >> - INIT_WORK(&dc->flush_expired_bios, flush_expired_bios); >> INIT_LIST_HEAD(&dc->delayed_bios); >> - mutex_init(&dc->timer_lock); >> atomic_set(&dc->may_delay, 1); >> dc->argc = argc; >> >> ret = delay_class_ctr(ti, &dc->read, argv); >> if (ret) >> goto bad; >> + max_delay = dc->read.delay; >> >> if (argc == 3) { >> ret = delay_class_ctr(ti, &dc->write, argv); >> @@ -206,6 +251,8 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) >> ret = delay_class_ctr(ti, &dc->flush, argv); >> if (ret) >> goto bad; >> + max_delay = max(max_delay, dc->write.delay); >> + max_delay = max(max_delay, dc->flush.delay); >> goto out; >> } >> >> @@ -216,19 +263,37 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) >> ret = delay_class_ctr(ti, &dc->flush, argv + 3); >> if (ret) >> goto bad; >> + max_delay = max(max_delay, dc->flush.delay); >> goto out; >> } >> >> ret = delay_class_ctr(ti, &dc->flush, argv + 6); >> if (ret) >> goto bad; >> + max_delay = max(max_delay, dc->flush.delay); >> >> out: >> - dc->kdelayd_wq = alloc_workqueue("kdelayd", WQ_MEM_RECLAIM, 0); >> - if (!dc->kdelayd_wq) { >> - ret = -EINVAL; >> - DMERR("Couldn't start kdelayd"); >> - goto bad; >> + if (max_delay < 50) { >> + /* >> + * In case of small requested delays, use kthread instead of >> + * timers and workqueue to achieve better latency. >> + */ >> + dc->worker = kthread_create(&flush_worker_fn, dc, >> + "dm-delay-flush-worker"); >> + if (IS_ERR(dc->worker)) { >> + ret = PTR_ERR(dc->worker); >> + goto bad; >> + } >> + } else { >> + timer_setup(&dc->delay_timer, handle_delayed_timer, 0); >> + INIT_WORK(&dc->flush_expired_bios, flush_expired_bios); >> + mutex_init(&dc->timer_lock); >> + dc->kdelayd_wq = alloc_workqueue("kdelayd", WQ_MEM_RECLAIM, 0); >> + if (!dc->kdelayd_wq) { >> + ret = -EINVAL; >> + DMERR("Couldn't start kdelayd"); >> + goto bad; >> + } >> } >> >> ti->num_flush_bios = 1; >> @@ -260,7 +325,10 @@ static int delay_bio(struct delay_c *dc, struct delay_class *c, struct bio *bio) >> list_add_tail(&delayed->list, &dc->delayed_bios); >> mutex_unlock(&delayed_bios_lock); >> >> - queue_timeout(dc, expires); >> + if (delay_is_fast(dc)) >> + wake_up_process(dc->worker); >> + else >> + queue_timeout(dc, expires); >> >> return DM_MAPIO_SUBMITTED; >> } >> @@ -270,8 +338,13 @@ static void delay_presuspend(struct dm_target *ti) >> struct delay_c *dc = ti->private; >> >> atomic_set(&dc->may_delay, 0); >> - del_timer_sync(&dc->delay_timer); >> - flush_bios(flush_delayed_bios(dc, 1)); >> + >> + if (delay_is_fast(dc)) >> + flush_delayed_bios_fast(dc, true); >> + else { >> + del_timer_sync(&dc->delay_timer); >> + flush_bios(flush_delayed_bios(dc, true)); >> + } >> } >> >> static void delay_resume(struct dm_target *ti) >> @@ -356,7 +429,7 @@ static int delay_iterate_devices(struct dm_target *ti, >> >> static struct target_type delay_target = { >> .name = "delay", >> - .version = {1, 3, 0}, >> + .version = {1, 4, 0}, >> .features = DM_TARGET_PASSES_INTEGRITY, >> .module = THIS_MODULE, >> .ctr = delay_ctr, >> > ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Patch "dm delay: for short delays, use kthread instead of timers and wq" has been added to the 6.6-stable tree 2023-11-29 10:02 ` Christian Loehle @ 2023-11-29 17:28 ` Mikulas Patocka 2023-11-29 17:38 ` Sasha Levin 0 siblings, 1 reply; 8+ messages in thread From: Mikulas Patocka @ 2023-11-29 17:28 UTC (permalink / raw) To: Christian Loehle Cc: Sasha Levin, stable-commits, stable, Alasdair Kergon, Mike Snitzer, dm-devel On Wed, 29 Nov 2023, Christian Loehle wrote: > Hi Mikulas, > Agreed and thanks for fixing. > Has this been selected for stable because of: > 6fc45b6ed921 ("dm-delay: fix a race between delay_presuspend and delay_bio") > If so, I would volunteer do the backports for that for you at least. I wouldn't backport this patch - it is an enhancement, not a bugfix, so it doesn't qualify for the stable kernel backports. Mikulas > BR, > Christian > > On 29/11/2023 08:28, Mikulas Patocka wrote: > > Hi > > > > This patch doesn't fix any bug (and introduces several serious bugs), so > > it shouldn't be backported at all. > > > > Mikulas > > > > > > On Tue, 28 Nov 2023, Sasha Levin wrote: > > > >> This is a note to let you know that I've just added the patch titled > >> > >> dm delay: for short delays, use kthread instead of timers and wq > >> > >> to the 6.6-stable tree which can be found at: > >> http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary > >> > >> The filename of the patch is: > >> dm-delay-for-short-delays-use-kthread-instead-of-tim.patch > >> and it can be found in the queue-6.6 subdirectory. > >> > >> If you, or anyone else, feels it should not be added to the stable tree, > >> please let <stable@vger.kernel.org> know about it. > >> > >> > >> > >> commit 976fd593415e170a8ed5db68683b280d5876982d > >> Author: Christian Loehle <christian.loehle@arm.com> > >> Date: Fri Oct 20 12:46:05 2023 +0100 > >> > >> dm delay: for short delays, use kthread instead of timers and wq > >> > >> [ Upstream commit 70bbeb29fab09d6ea6cfe64109db60a97d84d739 ] > >> > >> 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 <christian.loehle@arm.com> > >> [Harshit: kthread_create error handling fix in delay_ctr] > >> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com> > >> Signed-off-by: Mike Snitzer <snitzer@kernel.org> > >> Stable-dep-of: 6fc45b6ed921 ("dm-delay: fix a race between delay_presuspend and delay_bio") > >> Signed-off-by: Sasha Levin <sashal@kernel.org> > >> > >> diff --git a/drivers/md/dm-delay.c b/drivers/md/dm-delay.c > >> index 7433525e59856..efd510984e259 100644 > >> --- a/drivers/md/dm-delay.c > >> +++ b/drivers/md/dm-delay.c > >> @@ -13,6 +13,7 @@ > >> #include <linux/blkdev.h> > >> #include <linux/bio.h> > >> #include <linux/slab.h> > >> +#include <linux/kthread.h> > >> > >> #include <linux/device-mapper.h> > >> > >> @@ -31,6 +32,7 @@ struct delay_c { > >> struct workqueue_struct *kdelayd_wq; > >> struct work_struct flush_expired_bios; > >> struct list_head delayed_bios; > >> + struct task_struct *worker; > >> atomic_t may_delay; > >> > >> struct delay_class read; > >> @@ -66,6 +68,44 @@ static void queue_timeout(struct delay_c *dc, unsigned long expires) > >> mutex_unlock(&dc->timer_lock); > >> } > >> > >> +static inline bool delay_is_fast(struct delay_c *dc) > >> +{ > >> + return !!dc->worker; > >> +} > >> + > >> +static void flush_delayed_bios_fast(struct delay_c *dc, bool flush_all) > >> +{ > >> + struct dm_delay_info *delayed, *next; > >> + > >> + mutex_lock(&delayed_bios_lock); > >> + list_for_each_entry_safe(delayed, next, &dc->delayed_bios, list) { > >> + if (flush_all || time_after_eq(jiffies, delayed->expires)) { > >> + struct bio *bio = dm_bio_from_per_bio_data(delayed, > >> + sizeof(struct dm_delay_info)); > >> + list_del(&delayed->list); > >> + dm_submit_bio_remap(bio, NULL); > >> + delayed->class->ops--; > >> + } > >> + } > >> + mutex_unlock(&delayed_bios_lock); > >> +} > >> + > >> +static int flush_worker_fn(void *data) > >> +{ > >> + struct delay_c *dc = data; > >> + > >> + while (1) { > >> + flush_delayed_bios_fast(dc, false); > >> + if (unlikely(list_empty(&dc->delayed_bios))) { > >> + set_current_state(TASK_INTERRUPTIBLE); > >> + schedule(); > >> + } else > >> + cond_resched(); > >> + } > >> + > >> + return 0; > >> +} > >> + > >> static void flush_bios(struct bio *bio) > >> { > >> struct bio *n; > >> @@ -78,7 +118,7 @@ static void flush_bios(struct bio *bio) > >> } > >> } > >> > >> -static struct bio *flush_delayed_bios(struct delay_c *dc, int flush_all) > >> +static struct bio *flush_delayed_bios(struct delay_c *dc, bool flush_all) > >> { > >> struct dm_delay_info *delayed, *next; > >> unsigned long next_expires = 0; > >> @@ -115,7 +155,10 @@ static void flush_expired_bios(struct work_struct *work) > >> struct delay_c *dc; > >> > >> dc = container_of(work, struct delay_c, flush_expired_bios); > >> - flush_bios(flush_delayed_bios(dc, 0)); > >> + if (delay_is_fast(dc)) > >> + flush_delayed_bios_fast(dc, false); > >> + else > >> + flush_bios(flush_delayed_bios(dc, false)); > >> } > >> > >> static void delay_dtr(struct dm_target *ti) > >> @@ -131,8 +174,11 @@ static void delay_dtr(struct dm_target *ti) > >> dm_put_device(ti, dc->write.dev); > >> if (dc->flush.dev) > >> dm_put_device(ti, dc->flush.dev); > >> + if (dc->worker) > >> + kthread_stop(dc->worker); > >> > >> - mutex_destroy(&dc->timer_lock); > >> + if (!delay_is_fast(dc)) > >> + mutex_destroy(&dc->timer_lock); > >> > >> kfree(dc); > >> } > >> @@ -175,6 +221,7 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) > >> { > >> struct delay_c *dc; > >> int ret; > >> + unsigned int max_delay; > >> > >> if (argc != 3 && argc != 6 && argc != 9) { > >> ti->error = "Requires exactly 3, 6 or 9 arguments"; > >> @@ -188,16 +235,14 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) > >> } > >> > >> ti->private = dc; > >> - timer_setup(&dc->delay_timer, handle_delayed_timer, 0); > >> - INIT_WORK(&dc->flush_expired_bios, flush_expired_bios); > >> INIT_LIST_HEAD(&dc->delayed_bios); > >> - mutex_init(&dc->timer_lock); > >> atomic_set(&dc->may_delay, 1); > >> dc->argc = argc; > >> > >> ret = delay_class_ctr(ti, &dc->read, argv); > >> if (ret) > >> goto bad; > >> + max_delay = dc->read.delay; > >> > >> if (argc == 3) { > >> ret = delay_class_ctr(ti, &dc->write, argv); > >> @@ -206,6 +251,8 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) > >> ret = delay_class_ctr(ti, &dc->flush, argv); > >> if (ret) > >> goto bad; > >> + max_delay = max(max_delay, dc->write.delay); > >> + max_delay = max(max_delay, dc->flush.delay); > >> goto out; > >> } > >> > >> @@ -216,19 +263,37 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) > >> ret = delay_class_ctr(ti, &dc->flush, argv + 3); > >> if (ret) > >> goto bad; > >> + max_delay = max(max_delay, dc->flush.delay); > >> goto out; > >> } > >> > >> ret = delay_class_ctr(ti, &dc->flush, argv + 6); > >> if (ret) > >> goto bad; > >> + max_delay = max(max_delay, dc->flush.delay); > >> > >> out: > >> - dc->kdelayd_wq = alloc_workqueue("kdelayd", WQ_MEM_RECLAIM, 0); > >> - if (!dc->kdelayd_wq) { > >> - ret = -EINVAL; > >> - DMERR("Couldn't start kdelayd"); > >> - goto bad; > >> + if (max_delay < 50) { > >> + /* > >> + * In case of small requested delays, use kthread instead of > >> + * timers and workqueue to achieve better latency. > >> + */ > >> + dc->worker = kthread_create(&flush_worker_fn, dc, > >> + "dm-delay-flush-worker"); > >> + if (IS_ERR(dc->worker)) { > >> + ret = PTR_ERR(dc->worker); > >> + goto bad; > >> + } > >> + } else { > >> + timer_setup(&dc->delay_timer, handle_delayed_timer, 0); > >> + INIT_WORK(&dc->flush_expired_bios, flush_expired_bios); > >> + mutex_init(&dc->timer_lock); > >> + dc->kdelayd_wq = alloc_workqueue("kdelayd", WQ_MEM_RECLAIM, 0); > >> + if (!dc->kdelayd_wq) { > >> + ret = -EINVAL; > >> + DMERR("Couldn't start kdelayd"); > >> + goto bad; > >> + } > >> } > >> > >> ti->num_flush_bios = 1; > >> @@ -260,7 +325,10 @@ static int delay_bio(struct delay_c *dc, struct delay_class *c, struct bio *bio) > >> list_add_tail(&delayed->list, &dc->delayed_bios); > >> mutex_unlock(&delayed_bios_lock); > >> > >> - queue_timeout(dc, expires); > >> + if (delay_is_fast(dc)) > >> + wake_up_process(dc->worker); > >> + else > >> + queue_timeout(dc, expires); > >> > >> return DM_MAPIO_SUBMITTED; > >> } > >> @@ -270,8 +338,13 @@ static void delay_presuspend(struct dm_target *ti) > >> struct delay_c *dc = ti->private; > >> > >> atomic_set(&dc->may_delay, 0); > >> - del_timer_sync(&dc->delay_timer); > >> - flush_bios(flush_delayed_bios(dc, 1)); > >> + > >> + if (delay_is_fast(dc)) > >> + flush_delayed_bios_fast(dc, true); > >> + else { > >> + del_timer_sync(&dc->delay_timer); > >> + flush_bios(flush_delayed_bios(dc, true)); > >> + } > >> } > >> > >> static void delay_resume(struct dm_target *ti) > >> @@ -356,7 +429,7 @@ static int delay_iterate_devices(struct dm_target *ti, > >> > >> static struct target_type delay_target = { > >> .name = "delay", > >> - .version = {1, 3, 0}, > >> + .version = {1, 4, 0}, > >> .features = DM_TARGET_PASSES_INTEGRITY, > >> .module = THIS_MODULE, > >> .ctr = delay_ctr, > >> > > > ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Patch "dm delay: for short delays, use kthread instead of timers and wq" has been added to the 6.6-stable tree 2023-11-29 17:28 ` Mikulas Patocka @ 2023-11-29 17:38 ` Sasha Levin 2023-11-29 18:16 ` Mikulas Patocka 0 siblings, 1 reply; 8+ messages in thread From: Sasha Levin @ 2023-11-29 17:38 UTC (permalink / raw) To: Mikulas Patocka Cc: Christian Loehle, stable-commits, stable, Alasdair Kergon, Mike Snitzer, dm-devel On Wed, Nov 29, 2023 at 06:28:16PM +0100, Mikulas Patocka wrote: > > >On Wed, 29 Nov 2023, Christian Loehle wrote: > >> Hi Mikulas, >> Agreed and thanks for fixing. >> Has this been selected for stable because of: >> 6fc45b6ed921 ("dm-delay: fix a race between delay_presuspend and delay_bio") >> If so, I would volunteer do the backports for that for you at least. > >I wouldn't backport this patch - it is an enhancement, not a bugfix, so it >doesn't qualify for the stable kernel backports. Right - this watch was selected as a dependency for 6fc45b6ed921 ("dm-delay: fix a race between delay_presuspend and delay_bio"). In general, unless it's impractical, we'd rather take a dependency chain rather than deal with a non-trivial backport as those tend to have issues longer term. -- Thanks, Sasha ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Patch "dm delay: for short delays, use kthread instead of timers and wq" has been added to the 6.6-stable tree 2023-11-29 17:38 ` Sasha Levin @ 2023-11-29 18:16 ` Mikulas Patocka 2023-11-29 18:52 ` Sasha Levin 0 siblings, 1 reply; 8+ messages in thread From: Mikulas Patocka @ 2023-11-29 18:16 UTC (permalink / raw) To: Sasha Levin Cc: Christian Loehle, stable-commits, stable, Alasdair Kergon, Mike Snitzer, dm-devel On Wed, 29 Nov 2023, Sasha Levin wrote: > On Wed, Nov 29, 2023 at 06:28:16PM +0100, Mikulas Patocka wrote: > > > > > >On Wed, 29 Nov 2023, Christian Loehle wrote: > > > >> Hi Mikulas, > >> Agreed and thanks for fixing. > >> Has this been selected for stable because of: > >> 6fc45b6ed921 ("dm-delay: fix a race between delay_presuspend and > >> delay_bio") > >> If so, I would volunteer do the backports for that for you at least. > > > >I wouldn't backport this patch - it is an enhancement, not a bugfix, so it > >doesn't qualify for the stable kernel backports. > > Right - this watch was selected as a dependency for 6fc45b6ed921 > ("dm-delay: fix a race between delay_presuspend and delay_bio"). > > In general, unless it's impractical, we'd rather take a dependency chain > rather than deal with a non-trivial backport as those tend to have > issues longer term. > > -- > Thanks, > Sasha The patch 70bbeb29fab0 ("dm delay: for short delays, use kthread instead of timers and wq") changes behavior of dm-delay from using timers to polling, so it may cause problems to people running legacy kernels - the polling consumes more CPU time than the timers - so I think it shouldn't go to the stable kernels where users expect that there will be no functional change. Here I'm submitting the patch 6fc45b6ed921 backported for 6.6.3. Mikulas From: Mikulas Patocka <mpatocka@redhat.com> dm-delay: fix a race between delay_presuspend and delay_bio 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 theread executes delay_presuspend, it sets, dc->may_delay to zero, deletes the timer and flushes pending bios. Now, the first thread continues and adds the bio to delayed->list despite the fact that dc->may_delay is false. In order to fix this bug, we change may_delay's type from atomic_t to bool and we read and write it only 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 <mpatocka@redhat.com> Cc: stable@vger.kernel.org --- drivers/md/dm-delay.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) Index: linux-stable/drivers/md/dm-delay.c =================================================================== --- linux-stable.orig/drivers/md/dm-delay.c 2023-11-29 19:03:03.000000000 +0100 +++ linux-stable/drivers/md/dm-delay.c 2023-11-29 19:03:03.000000000 +0100 @@ -31,7 +31,7 @@ struct delay_c { struct workqueue_struct *kdelayd_wq; struct work_struct flush_expired_bios; struct list_head delayed_bios; - atomic_t may_delay; + bool may_delay; struct delay_class read; struct delay_class write; @@ -192,7 +192,7 @@ static int delay_ctr(struct dm_target *t INIT_WORK(&dc->flush_expired_bios, flush_expired_bios); INIT_LIST_HEAD(&dc->delayed_bios); mutex_init(&dc->timer_lock); - atomic_set(&dc->may_delay, 1); + dc->may_delay = true; dc->argc = argc; ret = delay_class_ctr(ti, &dc->read, argv); @@ -247,7 +247,7 @@ static int delay_bio(struct delay_c *dc, struct dm_delay_info *delayed; unsigned long expires = 0; - if (!c->delay || !atomic_read(&dc->may_delay)) + if (!c->delay) return DM_MAPIO_REMAPPED; delayed = dm_per_bio_data(bio, sizeof(struct dm_delay_info)); @@ -256,6 +256,10 @@ static int delay_bio(struct delay_c *dc, delayed->expires = expires = jiffies + msecs_to_jiffies(c->delay); mutex_lock(&delayed_bios_lock); + if (unlikely(!dc->may_delay)) { + mutex_unlock(&delayed_bios_lock); + return DM_MAPIO_REMAPPED; + } c->ops++; list_add_tail(&delayed->list, &dc->delayed_bios); mutex_unlock(&delayed_bios_lock); @@ -269,7 +273,10 @@ static void delay_presuspend(struct dm_t { struct delay_c *dc = ti->private; - atomic_set(&dc->may_delay, 0); + mutex_lock(&delayed_bios_lock); + dc->may_delay = false; + mutex_unlock(&delayed_bios_lock); + del_timer_sync(&dc->delay_timer); flush_bios(flush_delayed_bios(dc, 1)); } @@ -278,7 +285,7 @@ static void delay_resume(struct dm_targe { struct delay_c *dc = ti->private; - atomic_set(&dc->may_delay, 1); + dc->may_delay = true; } static int delay_map(struct dm_target *ti, struct bio *bio) ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Patch "dm delay: for short delays, use kthread instead of timers and wq" has been added to the 6.6-stable tree 2023-11-29 18:16 ` Mikulas Patocka @ 2023-11-29 18:52 ` Sasha Levin 2023-11-29 19:02 ` Mikulas Patocka 0 siblings, 1 reply; 8+ messages in thread From: Sasha Levin @ 2023-11-29 18:52 UTC (permalink / raw) To: Mikulas Patocka Cc: Christian Loehle, stable-commits, stable, Alasdair Kergon, Mike Snitzer, dm-devel On Wed, Nov 29, 2023 at 07:16:52PM +0100, Mikulas Patocka wrote: > > >On Wed, 29 Nov 2023, Sasha Levin wrote: > >> On Wed, Nov 29, 2023 at 06:28:16PM +0100, Mikulas Patocka wrote: >> > >> > >> >On Wed, 29 Nov 2023, Christian Loehle wrote: >> > >> >> Hi Mikulas, >> >> Agreed and thanks for fixing. >> >> Has this been selected for stable because of: >> >> 6fc45b6ed921 ("dm-delay: fix a race between delay_presuspend and >> >> delay_bio") >> >> If so, I would volunteer do the backports for that for you at least. >> > >> >I wouldn't backport this patch - it is an enhancement, not a bugfix, so it >> >doesn't qualify for the stable kernel backports. >> >> Right - this watch was selected as a dependency for 6fc45b6ed921 >> ("dm-delay: fix a race between delay_presuspend and delay_bio"). >> >> In general, unless it's impractical, we'd rather take a dependency chain >> rather than deal with a non-trivial backport as those tend to have >> issues longer term. >> >> -- >> Thanks, >> Sasha > >The patch 70bbeb29fab0 ("dm delay: for short delays, use kthread instead >of timers and wq") changes behavior of dm-delay from using timers to >polling, so it may cause problems to people running legacy kernels - the >polling consumes more CPU time than the timers - so I think it shouldn't >go to the stable kernels where users expect that there will be no >functional change. > >Here I'm submitting the patch 6fc45b6ed921 backported for 6.6.3. Is this okay for 6.1 too? -- Thanks, Sasha ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Patch "dm delay: for short delays, use kthread instead of timers and wq" has been added to the 6.6-stable tree 2023-11-29 18:52 ` Sasha Levin @ 2023-11-29 19:02 ` Mikulas Patocka 2023-11-29 20:00 ` Sasha Levin 0 siblings, 1 reply; 8+ messages in thread From: Mikulas Patocka @ 2023-11-29 19:02 UTC (permalink / raw) To: Sasha Levin Cc: Christian Loehle, stable-commits, stable, Alasdair Kergon, Mike Snitzer, dm-devel On Wed, 29 Nov 2023, Sasha Levin wrote: > On Wed, Nov 29, 2023 at 07:16:52PM +0100, Mikulas Patocka wrote: > > > > > >On Wed, 29 Nov 2023, Sasha Levin wrote: > > > >> On Wed, Nov 29, 2023 at 06:28:16PM +0100, Mikulas Patocka wrote: > >> > > >> > > >> >On Wed, 29 Nov 2023, Christian Loehle wrote: > >> > > >> >> Hi Mikulas, > >> >> Agreed and thanks for fixing. > >> >> Has this been selected for stable because of: > >> >> 6fc45b6ed921 ("dm-delay: fix a race between delay_presuspend and > >> >> delay_bio") > >> >> If so, I would volunteer do the backports for that for you at least. > >> > > >> >I wouldn't backport this patch - it is an enhancement, not a bugfix, so it > >> >doesn't qualify for the stable kernel backports. > >> > >> Right - this watch was selected as a dependency for 6fc45b6ed921 > >> ("dm-delay: fix a race between delay_presuspend and delay_bio"). > >> > >> In general, unless it's impractical, we'd rather take a dependency chain > >> rather than deal with a non-trivial backport as those tend to have > >> issues longer term. > >> > >> -- > >> Thanks, > >> Sasha > > > >The patch 70bbeb29fab0 ("dm delay: for short delays, use kthread instead > >of timers and wq") changes behavior of dm-delay from using timers to > >polling, so it may cause problems to people running legacy kernels - the > >polling consumes more CPU time than the timers - so I think it shouldn't > >go to the stable kernels where users expect that there will be no > >functional change. > > > >Here I'm submitting the patch 6fc45b6ed921 backported for 6.6.3. > > Is this okay for 6.1 too? Yes, it is. It applies to kernels as old as 4.19. Mikulas ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Patch "dm delay: for short delays, use kthread instead of timers and wq" has been added to the 6.6-stable tree 2023-11-29 19:02 ` Mikulas Patocka @ 2023-11-29 20:00 ` Sasha Levin 0 siblings, 0 replies; 8+ messages in thread From: Sasha Levin @ 2023-11-29 20:00 UTC (permalink / raw) To: Mikulas Patocka Cc: Christian Loehle, stable-commits, stable, Alasdair Kergon, Mike Snitzer, dm-devel On Wed, Nov 29, 2023 at 08:02:23PM +0100, Mikulas Patocka wrote: > > >On Wed, 29 Nov 2023, Sasha Levin wrote: > >> On Wed, Nov 29, 2023 at 07:16:52PM +0100, Mikulas Patocka wrote: >> > >> > >> >On Wed, 29 Nov 2023, Sasha Levin wrote: >> > >> >> On Wed, Nov 29, 2023 at 06:28:16PM +0100, Mikulas Patocka wrote: >> >> > >> >> > >> >> >On Wed, 29 Nov 2023, Christian Loehle wrote: >> >> > >> >> >> Hi Mikulas, >> >> >> Agreed and thanks for fixing. >> >> >> Has this been selected for stable because of: >> >> >> 6fc45b6ed921 ("dm-delay: fix a race between delay_presuspend and >> >> >> delay_bio") >> >> >> If so, I would volunteer do the backports for that for you at least. >> >> > >> >> >I wouldn't backport this patch - it is an enhancement, not a bugfix, so it >> >> >doesn't qualify for the stable kernel backports. >> >> >> >> Right - this watch was selected as a dependency for 6fc45b6ed921 >> >> ("dm-delay: fix a race between delay_presuspend and delay_bio"). >> >> >> >> In general, unless it's impractical, we'd rather take a dependency chain >> >> rather than deal with a non-trivial backport as those tend to have >> >> issues longer term. >> >> >> >> -- >> >> Thanks, >> >> Sasha >> > >> >The patch 70bbeb29fab0 ("dm delay: for short delays, use kthread instead >> >of timers and wq") changes behavior of dm-delay from using timers to >> >polling, so it may cause problems to people running legacy kernels - the >> >polling consumes more CPU time than the timers - so I think it shouldn't >> >go to the stable kernels where users expect that there will be no >> >functional change. >> > >> >Here I'm submitting the patch 6fc45b6ed921 backported for 6.6.3. >> >> Is this okay for 6.1 too? > >Yes, it is. It applies to kernels as old as 4.19. Great, applied all the way back to 4.19. Thanks! -- Thanks, Sasha ^ permalink raw reply [flat|nested] 8+ messages in thread
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2023-11-29 8:28 ` Patch "dm delay: for short delays, use kthread instead of timers and wq" has been added to the 6.6-stable tree Mikulas Patocka
2023-11-29 10:02 ` Christian Loehle
2023-11-29 17:28 ` Mikulas Patocka
2023-11-29 17:38 ` Sasha Levin
2023-11-29 18:16 ` Mikulas Patocka
2023-11-29 18:52 ` Sasha Levin
2023-11-29 19:02 ` Mikulas Patocka
2023-11-29 20:00 ` Sasha Levin
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