linux-kernel - Re: [patch] v2 mm/slub: restore/expand unfreeze

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Date:   Mon, 19 Jul 2021 15:15:38 +0200
From:   Mike Galbraith <efault@....de>
To:     Vlastimil Babka <vbabka@...e.cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     linux-rt-users@...r.kernel.org,
        Mel Gorman <mgorman@...hsingularity.net>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [patch] v2 mm/slub: restore/expand unfreeze_partials() local
 exclusion scope

On Mon, 2021-07-19 at 06:01 +0200, Mike Galbraith wrote:
>
> ... despite the unlock/relock in this patch, it still manages to be a
> -ENOBOOT.

The somewhat bent up half of your patch below has been chugging away
long enough for me to speculate that __slab_free() vs ___slab_alloc()
is the *only* player in the explosion varieties I've been seeing.

---
 mm/slub.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2484,6 +2484,9 @@ static void put_cpu_partial(struct kmem_
 	int pobjects;

 	slub_get_cpu_ptr(s->cpu_slab);
+	/* __slab_free() vs ___slab_alloc() critical sections */
+	if (IS_ENABLED(CONFIG_PREEMPT_RT) && drain)
+		local_lock(&s->cpu_slab->lock);
 	do {
 		pages = 0;
 		pobjects = 0;
@@ -2497,7 +2500,13 @@ static void put_cpu_partial(struct kmem_
 				 * partial array is full. Move the existing
 				 * set to the per node partial list.
 				 */
-				unfreeze_partials(s);
+				this_cpu_write(s->cpu_slab->partial, NULL);
+				if (IS_ENABLED(CONFIG_PREEMPT_RT) && drain)
+					local_unlock(&s->cpu_slab->lock);
+				__unfreeze_partials(s, oldpage);
+				if (IS_ENABLED(CONFIG_PREEMPT_RT) && drain)
+					local_lock(&s->cpu_slab->lock);
+
 				oldpage = NULL;
 				pobjects = 0;
 				pages = 0;
@@ -2514,6 +2523,8 @@ static void put_cpu_partial(struct kmem_

 	} while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page)
 								!= oldpage);
+	if (IS_ENABLED(CONFIG_PREEMPT_RT) && drain)
+		local_unlock(&s->cpu_slab->lock);
 	slub_put_cpu_ptr(s->cpu_slab);
 #endif	/* CONFIG_SLUB_CPU_PARTIAL */
 }