[020/147] mm, slub: call deactivate_slab() without disabling irqs

Commit Message

Andrew Morton Sept. 8, 2021, 2:54 a.m. UTC

From: Vlastimil Babka <[e-mail]>
Subject: mm, slub: call deactivate_slab() without disabling irqs

The function is now safe to be called with irqs enabled, so move the calls
outside of irq disabled sections.

When called from ___slab_alloc() -> flush_slab() we have irqs disabled, so
to reenable them before deactivate_slab() we need to open-code
flush_slab() in ___slab_alloc() and reenable irqs after modifying the
kmem_cache_cpu fields.  But that means a IRQ handler meanwhile might have
assigned a new page to kmem_cache_cpu.page so we have to retry the whole
check.

The remaining callers of flush_slab() are the IPI handler which has
disabled irqs anyway, and slub_cpu_dead() which will be dealt with in the
following patch.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Vlastimil Babka <[e-mail]>
Cc: Christoph Lameter <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Jann Horn <[e-mail]>
Cc: Jesper Dangaard Brouer <[e-mail]>
Cc: Joonsoo Kim <[e-mail]>
Cc: Mel Gorman <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Cc: Pekka Enberg <[e-mail]>
Cc: Qian Cai <[e-mail]>
Cc: Sebastian Andrzej Siewior <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/slub.c |   24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

Patch

--- a/mm/slub.c~mm-slub-call-deactivate_slab-without-disabling-irqs
+++ a/mm/slub.c
@@ -2779,8 +2779,8 @@  deactivate_slab:
 	freelist = c->freelist;
 	c->page = NULL;
 	c->freelist = NULL;
-	deactivate_slab(s, page, freelist);
 	local_irq_restore(flags);
+	deactivate_slab(s, page, freelist);
 
 new_slab:
 
@@ -2848,18 +2848,32 @@  check_new_page:
 		 */
 		goto return_single;
 
+retry_load_page:
+
 	local_irq_save(flags);
-	if (unlikely(c->page))
-		flush_slab(s, c);
+	if (unlikely(c->page)) {
+		void *flush_freelist = c->freelist;
+		struct page *flush_page = c->page;
+
+		c->page = NULL;
+		c->freelist = NULL;
+		c->tid = next_tid(c->tid);
+
+		local_irq_restore(flags);
+
+		deactivate_slab(s, flush_page, flush_freelist);
+
+		stat(s, CPUSLAB_FLUSH);
+
+		goto retry_load_page;
+	}
 	c->page = page;
 
 	goto load_freelist;
 
 return_single:
 
-	local_irq_save(flags);
 	deactivate_slab(s, page, get_freepointer(s, freelist));
-	local_irq_restore(flags);
 	return freelist;
 }