summaryrefslogtreecommitdiff
path: root/mm/slab_common.c
diff options
context:
space:
mode:
authorVlastimil Babka <vbabka@suse.cz>2021-02-24 23:01:12 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-02-25 00:38:27 +0300
commit7e1fa93deff44677a94dfc323ff629bbf5cf9360 (patch)
tree693222436aafe91bdab6e78d1d0b916d139431fa /mm/slab_common.c
parent666716fd267df0007dfbb6480cd79dd5b05da4cc (diff)
downloadlinux-7e1fa93deff44677a94dfc323ff629bbf5cf9360.tar.xz
mm, slab, slub: stop taking memory hotplug lock
Since commit 03afc0e25f7f ("slab: get_online_mems for kmem_cache_{create,destroy,shrink}") we are taking memory hotplug lock for SLAB and SLUB when creating, destroying or shrinking a cache. It is quite a heavy lock and it's best to avoid it if possible, as we had several issues with lockdep complaining about ordering in the past, see e.g. e4f8e513c3d3 ("mm/slub: fix a deadlock in show_slab_objects()"). The problem scenario in 03afc0e25f7f (solved by the memory hotplug lock) can be summarized as follows: while there's slab_mutex synchronizing new kmem cache creation and SLUB's MEM_GOING_ONLINE callback slab_mem_going_online_callback(), we may miss creation of kmem_cache_node for the hotplugged node in the new kmem cache, because the hotplug callback doesn't yet see the new cache, and cache creation in init_kmem_cache_nodes() only inits kmem_cache_node for nodes in the N_NORMAL_MEMORY nodemask, which however may not yet include the new node, as that happens only later after the MEM_GOING_ONLINE callback. Instead of using get/put_online_mems(), the problem can be solved by SLUB maintaining its own nodemask of nodes for which it has allocated the per-node kmem_cache_node structures. This nodemask would generally mirror the N_NORMAL_MEMORY nodemask, but would be updated only in under SLUB's control in its memory hotplug callbacks under the slab_mutex. This patch adds such nodemask and its handling. Commit 03afc0e25f7f mentiones "issues like [the one above]", but there don't appear to be further issues. All the paths (shared for SLAB and SLUB) taking the memory hotplug locks are also taking the slab_mutex, except kmem_cache_shrink() where 03afc0e25f7f replaced slab_mutex with get/put_online_mems(). We however cannot simply restore slab_mutex in kmem_cache_shrink(), as SLUB can enters the function from a write to sysfs 'shrink' file, thus holding kernfs lock, and in kmem_cache_create() the kernfs lock is nested within slab_mutex. But on closer inspection we don't actually need to protect kmem_cache_shrink() from hotplug callbacks: While SLUB's __kmem_cache_shrink() does for_each_kmem_cache_node(), missing a new node added in parallel hotplug is not fatal, and parallel hotremove does not free kmem_cache_node's anymore after the previous patch, so use-after free cannot happen. The per-node shrinking itself is protected by n->list_lock. Same is true for SLAB, and SLOB is no-op. SLAB also doesn't need the memory hotplug locking, which it only gained by 03afc0e25f7f through the shared paths in slab_common.c. Its memory hotplug callbacks are also protected by slab_mutex against races with these paths. The problem of SLUB relying on N_NORMAL_MEMORY doesn't apply to SLAB, as its setup_kmem_cache_nodes relies on N_ONLINE, and the new node is already set there during the MEM_GOING_ONLINE callback, so no special care is needed for SLAB. As such, this patch removes all get/put_online_mems() usage by the slab subsystem. Link: https://lkml.kernel.org/r/20210113131634.3671-3-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Cc: Christoph Lameter <cl@linux.com> Cc: David Hildenbrand <david@redhat.com> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Pekka Enberg <penberg@kernel.org> Cc: Qian Cai <cai@redhat.com> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/slab_common.c')
-rw-r--r--mm/slab_common.c8
1 files changed, 2 insertions, 6 deletions
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 580124b7fed8..d73bea53f759 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -310,7 +310,6 @@ kmem_cache_create_usercopy(const char *name,
int err;
get_online_cpus();
- get_online_mems();
mutex_lock(&slab_mutex);
@@ -360,7 +359,6 @@ kmem_cache_create_usercopy(const char *name,
out_unlock:
mutex_unlock(&slab_mutex);
- put_online_mems();
put_online_cpus();
if (err) {
@@ -487,7 +485,6 @@ void kmem_cache_destroy(struct kmem_cache *s)
return;
get_online_cpus();
- get_online_mems();
mutex_lock(&slab_mutex);
@@ -504,7 +501,6 @@ void kmem_cache_destroy(struct kmem_cache *s)
out_unlock:
mutex_unlock(&slab_mutex);
- put_online_mems();
put_online_cpus();
}
EXPORT_SYMBOL(kmem_cache_destroy);
@@ -523,10 +519,10 @@ int kmem_cache_shrink(struct kmem_cache *cachep)
int ret;
get_online_cpus();
- get_online_mems();
+
kasan_cache_shrink(cachep);
ret = __kmem_cache_shrink(cachep);
- put_online_mems();
+
put_online_cpus();
return ret;
}