Commit 5a836bf6b09f ("mm: slub: move flush_cpu_slab() invocations
__free_slab() invocations out of IRQ context") moved all flush_cpu_slab()
invocations to the global workqueue to avoid a problem related
with deactivate_slab()/__free_slab() being called from an IRQ context
on PREEMPT_RT kernels.
When the flush_all_cpu_locked() function is called from a task context
it may happen that a workqueue with WQ_MEM_RECLAIM bit set ends up
flushing the global workqueue, this will cause a dependency issue.
workqueue: WQ_MEM_RECLAIM nvme-delete-wq:nvme_delete_ctrl_work [nvme_core]
is flushing !WQ_MEM_RECLAIM events:flush_cpu_slab
WARNING: CPU: 37 PID: 410 at kernel/workqueue.c:2637
check_flush_dependency+0x10a/0x120
Workqueue: nvme-delete-wq nvme_delete_ctrl_work [nvme_core]
RIP: 0010:check_flush_dependency+0x10a/0x120[ 453.262125] Call Trace:
__flush_work.isra.0+0xbf/0x220
? __queue_work+0x1dc/0x420
flush_all_cpus_locked+0xfb/0x120
__kmem_cache_shutdown+0x2b/0x320
kmem_cache_destroy+0x49/0x100
bioset_exit+0x143/0x190
blk_release_queue+0xb9/0x100
kobject_cleanup+0x37/0x130
nvme_fc_ctrl_free+0xc6/0x150 [nvme_fc]
nvme_free_ctrl+0x1ac/0x2b0 [nvme_core]
Fix this bug by creating a workqueue for the flush operation with
the WQ_MEM_RECLAIM bit set.
v2: Create a workqueue with WQ_MEM_RECLAIM
instead of trying to revert the changes.
Signed-off-by: Maurizio Lombardi <[email protected]>
---
mm/slub.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/mm/slub.c b/mm/slub.c
index 862dbd9af4f5..cdb8011884d0 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -310,6 +310,11 @@ static inline void stat(const struct kmem_cache *s, enum stat_item si)
*/
static nodemask_t slab_nodes;
+/*
+ * Workqueue used for flush_cpu_slab().
+ */
+static struct workqueue_struct *flushwq;
+
/********************************************************************
* Core slab cache functions
*******************************************************************/
@@ -2730,7 +2735,7 @@ static void flush_all_cpus_locked(struct kmem_cache *s)
INIT_WORK(&sfw->work, flush_cpu_slab);
sfw->skip = false;
sfw->s = s;
- schedule_work_on(cpu, &sfw->work);
+ queue_work_on(cpu, flushwq, &sfw->work);
}
for_each_online_cpu(cpu) {
@@ -4858,6 +4863,8 @@ void __init kmem_cache_init(void)
void __init kmem_cache_init_late(void)
{
+ flushwq = create_workqueue("slub_flushwq");
+ BUG_ON(!flushwq);
}
struct kmem_cache *
--
2.31.1
On Mon, Sep 12, 2022 at 06:11:40PM +0200, Maurizio Lombardi wrote:
> Commit 5a836bf6b09f ("mm: slub: move flush_cpu_slab() invocations
> __free_slab() invocations out of IRQ context") moved all flush_cpu_slab()
> invocations to the global workqueue to avoid a problem related
> with deactivate_slab()/__free_slab() being called from an IRQ context
> on PREEMPT_RT kernels.
>
> When the flush_all_cpu_locked() function is called from a task context
> it may happen that a workqueue with WQ_MEM_RECLAIM bit set ends up
> flushing the global workqueue, this will cause a dependency issue.
>
> workqueue: WQ_MEM_RECLAIM nvme-delete-wq:nvme_delete_ctrl_work [nvme_core]
> is flushing !WQ_MEM_RECLAIM events:flush_cpu_slab
> WARNING: CPU: 37 PID: 410 at kernel/workqueue.c:2637
> check_flush_dependency+0x10a/0x120
> Workqueue: nvme-delete-wq nvme_delete_ctrl_work [nvme_core]
> RIP: 0010:check_flush_dependency+0x10a/0x120[ 453.262125] Call Trace:
> __flush_work.isra.0+0xbf/0x220
> ? __queue_work+0x1dc/0x420
> flush_all_cpus_locked+0xfb/0x120
> __kmem_cache_shutdown+0x2b/0x320
> kmem_cache_destroy+0x49/0x100
> bioset_exit+0x143/0x190
> blk_release_queue+0xb9/0x100
> kobject_cleanup+0x37/0x130
> nvme_fc_ctrl_free+0xc6/0x150 [nvme_fc]
> nvme_free_ctrl+0x1ac/0x2b0 [nvme_core]
>
> Fix this bug by creating a workqueue for the flush operation with
> the WQ_MEM_RECLAIM bit set.
>
> v2: Create a workqueue with WQ_MEM_RECLAIM
> instead of trying to revert the changes.
>
> Signed-off-by: Maurizio Lombardi <[email protected]>
> ---
> mm/slub.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 862dbd9af4f5..cdb8011884d0 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -310,6 +310,11 @@ static inline void stat(const struct kmem_cache *s, enum stat_item si)
> */
> static nodemask_t slab_nodes;
>
> +/*
> + * Workqueue used for flush_cpu_slab().
> + */
> +static struct workqueue_struct *flushwq;
> +
> /********************************************************************
> * Core slab cache functions
> *******************************************************************/
> @@ -2730,7 +2735,7 @@ static void flush_all_cpus_locked(struct kmem_cache *s)
> INIT_WORK(&sfw->work, flush_cpu_slab);
> sfw->skip = false;
> sfw->s = s;
> - schedule_work_on(cpu, &sfw->work);
> + queue_work_on(cpu, flushwq, &sfw->work);
> }
>
> for_each_online_cpu(cpu) {
> @@ -4858,6 +4863,8 @@ void __init kmem_cache_init(void)
>
> void __init kmem_cache_init_late(void)
> {
> + flushwq = create_workqueue("slub_flushwq");
> + BUG_ON(!flushwq);
> }
>
> struct kmem_cache *
> --
> 2.31.1
>
No objection about this patch,
but it seems create_workqueue is deprecated?
--
Thanks,
Hyeonggon
čt 15. 9. 2022 v 14:48 odesílatel Hyeonggon Yoo <[email protected]> napsal:
> No objection about this patch,
> but it seems create_workqueue is deprecated?
You're right, the documentation says that create_workqueue() is deprecated,
too bad there is not a comment in the source code.
Thanks for reporting this.
I will wait for the maintainers to review this one and eventually I
will submit a V3.
Maurizio
>
>
> --
> Thanks,
> Hyeonggon
>
On 9/12/22 18:11, Maurizio Lombardi wrote:
> @@ -2730,7 +2735,7 @@ static void flush_all_cpus_locked(struct kmem_cache *s)
> INIT_WORK(&sfw->work, flush_cpu_slab);
> sfw->skip = false;
> sfw->s = s;
> - schedule_work_on(cpu, &sfw->work);
> + queue_work_on(cpu, flushwq, &sfw->work);
> }
>
> for_each_online_cpu(cpu) {
> @@ -4858,6 +4863,8 @@ void __init kmem_cache_init(void)
>
> void __init kmem_cache_init_late(void)
> {
> + flushwq = create_workqueue("slub_flushwq");
> + BUG_ON(!flushwq);
Adding new BUG_ON is essentially prohibited these days, so please use WARN_ON().
Other than that deprecation issue, looks fine to me.
> }
>
> struct kmem_cache *
On 9/16/22 09:27, Maurizio Lombardi wrote:
> čt 15. 9. 2022 v 14:48 odesílatel Hyeonggon Yoo <[email protected]> napsal:
>> No objection about this patch,
>> but it seems create_workqueue is deprecated?
>
> You're right, the documentation says that create_workqueue() is deprecated,
> too bad there is not a comment in the source code.
Let's make Tejun and Lai aware of this.
> Thanks for reporting this.
>
> I will wait for the maintainers to review this one and eventually I
> will submit a V3.
>
> Maurizio
>
>
>
>>
>>
>> --
>> Thanks,
>> Hyeonggon
>>
>