Re: [PATCH v4 29/35] mm: slub: Move flush_cpu_slab() invocations __free_slab() invocations out of IRQ context
From: Vlastimil Babka <hidden>
Date: 2021-08-10 09:03:06
Also in:
lkml
Subsystem:
memory management, slab allocator, the rest · Maintainers:
Andrew Morton, Vlastimil Babka, Harry Yoo, Linus Torvalds
On 8/9/21 3:41 PM, Qian Cai wrote:
quoted
+static DEFINE_MUTEX(flush_lock); +static DEFINE_PER_CPU(struct slub_flush_work, slub_flush); + static void flush_all(struct kmem_cache *s) { - on_each_cpu_cond(has_cpu_slab, flush_cpu_slab, s, 1); + struct slub_flush_work *sfw; + unsigned int cpu; + + mutex_lock(&flush_lock);Vlastimil, taking the lock here could trigger a warning during memory offline/online due to the locking order: slab_mutex -> flush_lock [ 91.374541] WARNING: possible circular locking dependency detected [ 91.381411] 5.14.0-rc5-next-20210809+ #84 Not tainted [ 91.387149] ------------------------------------------------------ [ 91.394016] lsbug/1523 is trying to acquire lock: [ 91.399406] ffff800018e76530 (flush_lock){+.+.}-{3:3}, at: flush_all+0x50/0x1c8 [ 91.407425] but task is already holding lock: [ 91.414638] ffff800018e48468 (slab_mutex){+.+.}-{3:3}, at: slab_memory_callback+0x44/0x280 [ 91.423603] which lock already depends on the new lock.
OK, managed to reproduce in qemu and this fixes it for me on top of next-20210809. Could you test as well, as your testing might be more comprehensive? I will format is as a fixup for the proper patch in the series then. ----8<---- From 7ce71c7f9455e8b96dc1b728ea566b6ef5e424e4 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka <redacted> Date: Tue, 10 Aug 2021 10:58:07 +0200 Subject: [PATCH] mm, slub: fix memory offline lockdep splat Reverse order of flush_lock and cpus_read_lock() to prevent lockdep splat. In slab_mem_going_offline_callback() we already have cpus_read_lock() held so make sure it's not taken again. Signed-off-by: Vlastimil Babka <redacted> --- mm/slub.c | 27 ++++++++++++++++++++------- 1 file changed, 20 insertions(+), 7 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 88a6c3ed2751..073cdd4b020f 100644
--- a/mm/slub.c
+++ b/mm/slub.c@@ -2640,13 +2640,13 @@ static bool has_cpu_slab(int cpu, struct kmem_cache *s) static DEFINE_MUTEX(flush_lock); static DEFINE_PER_CPU(struct slub_flush_work, slub_flush); -static void flush_all(struct kmem_cache *s) +static void flush_all_cpus_locked(struct kmem_cache *s) { struct slub_flush_work *sfw; unsigned int cpu; + lockdep_assert_cpus_held(); mutex_lock(&flush_lock); - cpus_read_lock(); for_each_online_cpu(cpu) { sfw = &per_cpu(slub_flush, cpu);
@@ -2667,10 +2667,16 @@ static void flush_all(struct kmem_cache *s) flush_work(&sfw->work); } - cpus_read_unlock(); mutex_unlock(&flush_lock); } +static void flush_all(struct kmem_cache *s) +{ + cpus_read_lock(); + flush_all_cpus_locked(s); + cpus_read_unlock(); +} + /* * Use the cpu notifier to insure that the cpu slabs are flushed when * necessary.
@@ -4516,7 +4522,7 @@ EXPORT_SYMBOL(kfree); * being allocated from last increasing the chance that the last objects * are freed in them. */ -int __kmem_cache_shrink(struct kmem_cache *s) +int __kmem_cache_do_shrink(struct kmem_cache *s) { int node; int i;
@@ -4528,7 +4534,6 @@ int __kmem_cache_shrink(struct kmem_cache *s) unsigned long flags; int ret = 0; - flush_all(s); for_each_kmem_cache_node(s, node, n) { INIT_LIST_HEAD(&discard); for (i = 0; i < SHRINK_PROMOTE_MAX; i++)
@@ -4578,13 +4583,21 @@ int __kmem_cache_shrink(struct kmem_cache *s) return ret; } +int __kmem_cache_shrink(struct kmem_cache *s) +{ + flush_all(s); + return __kmem_cache_do_shrink(s); +} + static int slab_mem_going_offline_callback(void *arg) { struct kmem_cache *s; mutex_lock(&slab_mutex); - list_for_each_entry(s, &slab_caches, list) - __kmem_cache_shrink(s); + list_for_each_entry(s, &slab_caches, list) { + flush_all_cpus_locked(s); + __kmem_cache_do_shrink(s); + } mutex_unlock(&slab_mutex); return 0;
--
2.32.0