linux-kernel - [PATCH v6 19/33] mm, slub: make locking in deactivate

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Message-Id: <20210904105003.11688-20-vbabka@suse.cz>
Date:   Sat,  4 Sep 2021 12:49:49 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     linux-mm@...ck.org, Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Mike Galbraith <efault@....de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH v6 19/33] mm, slub: make locking in deactivate_slab() irq-safe

dectivate_slab() now no longer touches the kmem_cache_cpu structure, so it will
be possible to call it with irqs enabled. Just convert the spin_lock calls to
their irq saving/restoring variants to make it irq-safe.

Note we now have to use cmpxchg_double_slab() for irq-safe slab_lock(), because
in some situations we don't take the list_lock, which would disable irqs.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/slub.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index cea7a2ad9e3e..6deb4080ef54 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2223,6 +2223,7 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page,
 	enum slab_modes l = M_NONE, m = M_NONE;
 	void *nextfree, *freelist_iter, *freelist_tail;
 	int tail = DEACTIVATE_TO_HEAD;
+	unsigned long flags = 0;
 	struct page new;
 	struct page old;
 
@@ -2298,7 +2299,7 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page,
 			 * that acquire_slab() will see a slab page that
 			 * is frozen
 			 */
-			spin_lock(&n->list_lock);
+			spin_lock_irqsave(&n->list_lock, flags);
 		}
 	} else {
 		m = M_FULL;
@@ -2309,7 +2310,7 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page,
 			 * slabs from diagnostic functions will not see
 			 * any frozen slabs.
 			 */
-			spin_lock(&n->list_lock);
+			spin_lock_irqsave(&n->list_lock, flags);
 		}
 	}
 
@@ -2326,14 +2327,14 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page,
 	}
 
 	l = m;
-	if (!__cmpxchg_double_slab(s, page,
+	if (!cmpxchg_double_slab(s, page,
 				old.freelist, old.counters,
 				new.freelist, new.counters,
 				"unfreezing slab"))
 		goto redo;
 
 	if (lock)
-		spin_unlock(&n->list_lock);
+		spin_unlock_irqrestore(&n->list_lock, flags);
 
 	if (m == M_PARTIAL)
 		stat(s, tail);
-- 
2.33.0