| Message ID | 20220614220359.59282-4-longman@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/kmemleak: Avoid soft lockup in kmemleak_scan() | expand |
On Tue, Jun 14, 2022 at 06:03:59PM -0400, Waiman Long wrote: > diff --git a/mm/kmemleak.c b/mm/kmemleak.c > index 7dd64139a7c7..abba063ae5ee 100644 > --- a/mm/kmemleak.c > +++ b/mm/kmemleak.c > @@ -1417,12 +1417,16 @@ static void kmemleak_scan(void) > struct zone *zone; > int __maybe_unused i; > int new_leaks = 0; > + int loop1_cnt = 0; > > jiffies_last_scan = jiffies; > > /* prepare the kmemleak_object's */ > rcu_read_lock(); > list_for_each_entry_rcu(object, &object_list, object_list) { > + bool obj_pinned = false; > + > + loop1_cnt++; > raw_spin_lock_irq(&object->lock); > #ifdef DEBUG > /* > @@ -1437,10 +1441,32 @@ static void kmemleak_scan(void) > #endif > /* reset the reference count (whiten the object) */ > object->count = 0; > - if (color_gray(object) && get_object(object)) > + if (color_gray(object) && get_object(object)) { > list_add_tail(&object->gray_list, &gray_list); > + obj_pinned = true; > + } > > raw_spin_unlock_irq(&object->lock); > + > + /* > + * Do a cond_resched() to avoid soft lockup every 64k objects. > + * Make sure a reference has been taken so that the object > + * won't go away without RCU read lock. > + */ > + if (!(loop1_cnt & 0xffff)) { > + if (!obj_pinned && !get_object(object)) { > + /* Try the next object instead */ > + loop1_cnt--; > + continue; > + } With this trick we could probably get rid of rcu_read_lock() and take the kmemleak_lock instead. But that's for another patch. > + > + rcu_read_unlock(); > + cond_resched(); > + rcu_read_lock(); cond_resched_rcu() to save a couple of lines? > + > + if (!obj_pinned) > + put_object(object); > + } Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Thanks.
On 6/15/22 11:11, Catalin Marinas wrote: > On Tue, Jun 14, 2022 at 06:03:59PM -0400, Waiman Long wrote: >> diff --git a/mm/kmemleak.c b/mm/kmemleak.c >> index 7dd64139a7c7..abba063ae5ee 100644 >> --- a/mm/kmemleak.c >> +++ b/mm/kmemleak.c >> @@ -1417,12 +1417,16 @@ static void kmemleak_scan(void) >> struct zone *zone; >> int __maybe_unused i; >> int new_leaks = 0; >> + int loop1_cnt = 0; >> >> jiffies_last_scan = jiffies; >> >> /* prepare the kmemleak_object's */ >> rcu_read_lock(); >> list_for_each_entry_rcu(object, &object_list, object_list) { >> + bool obj_pinned = false; >> + >> + loop1_cnt++; >> raw_spin_lock_irq(&object->lock); >> #ifdef DEBUG >> /* >> @@ -1437,10 +1441,32 @@ static void kmemleak_scan(void) >> #endif >> /* reset the reference count (whiten the object) */ >> object->count = 0; >> - if (color_gray(object) && get_object(object)) >> + if (color_gray(object) && get_object(object)) { >> list_add_tail(&object->gray_list, &gray_list); >> + obj_pinned = true; >> + } >> >> raw_spin_unlock_irq(&object->lock); >> + >> + /* >> + * Do a cond_resched() to avoid soft lockup every 64k objects. >> + * Make sure a reference has been taken so that the object >> + * won't go away without RCU read lock. >> + */ >> + if (!(loop1_cnt & 0xffff)) { >> + if (!obj_pinned && !get_object(object)) { >> + /* Try the next object instead */ >> + loop1_cnt--; >> + continue; >> + } > With this trick we could probably get rid of rcu_read_lock() and take > the kmemleak_lock instead. But that's for another patch. rcu_read_lock() is cheap unless we use a preempt kernel. > >> + >> + rcu_read_unlock(); >> + cond_resched(); >> + rcu_read_lock(); > cond_resched_rcu() to save a couple of lines? I am not aware of such helper function. Yes, I should have used that instead in case I need to update this patch again. Thanks! > >> + >> + if (!obj_pinned) >> + put_object(object); >> + } > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Thanks, Longman
diff --git a/mm/kmemleak.c b/mm/kmemleak.c index 7dd64139a7c7..abba063ae5ee 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -1417,12 +1417,16 @@ static void kmemleak_scan(void) struct zone *zone; int __maybe_unused i; int new_leaks = 0; + int loop1_cnt = 0; jiffies_last_scan = jiffies; /* prepare the kmemleak_object's */ rcu_read_lock(); list_for_each_entry_rcu(object, &object_list, object_list) { + bool obj_pinned = false; + + loop1_cnt++; raw_spin_lock_irq(&object->lock); #ifdef DEBUG /* @@ -1437,10 +1441,32 @@ static void kmemleak_scan(void) #endif /* reset the reference count (whiten the object) */ object->count = 0; - if (color_gray(object) && get_object(object)) + if (color_gray(object) && get_object(object)) { list_add_tail(&object->gray_list, &gray_list); + obj_pinned = true; + } raw_spin_unlock_irq(&object->lock); + + /* + * Do a cond_resched() to avoid soft lockup every 64k objects. + * Make sure a reference has been taken so that the object + * won't go away without RCU read lock. + */ + if (!(loop1_cnt & 0xffff)) { + if (!obj_pinned && !get_object(object)) { + /* Try the next object instead */ + loop1_cnt--; + continue; + } + + rcu_read_unlock(); + cond_resched(); + rcu_read_lock(); + + if (!obj_pinned) + put_object(object); + } } rcu_read_unlock();
The first RCU-based object iteration loop has to modify the object count. So we cannot skip taking the object lock. One way to avoid soft lockup is to insert occasional cond_resched() call into the loop. This cannot be done while holding the RCU read lock which is to protect objects from being freed. However, taking a reference to the object will prevent it from being freed. We can then do a cond_resched() call after every 64k objects safely. Signed-off-by: Waiman Long <longman@redhat.com> --- mm/kmemleak.c | 28 +++++++++++++++++++++++++++- 1 file changed, 27 insertions(+), 1 deletion(-)