[2/6] mm, memcg: Prevent memory.max load tearing
diff mbox series

Message ID 50a31e5f39f8ae6c8fb73966ba1455f0924e8f44.1584034301.git.chris@chrisdown.name
State Accepted
Headers show
Series
  • mm, memcg: cgroup v2 tunable load/store tearing fixes
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Commit Message

Chris Down March 12, 2020, 5:32 p.m. UTC
This one is a bit more nuanced because we have memcg_max_mutex, which is
mostly just used for enforcing invariants, but we still need to
READ_ONCE since (despite its name) it doesn't really protect memory.max
access.

On write (page_counter_set_max() and memory_max_write()) we use xchg(),
which uses smp_mb(), so that's already fine.

Signed-off-by: Chris Down <chris@chrisdown.name>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: linux-mm@kvack.org
Cc: cgroups@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: kernel-team@fb.com
---
 mm/memcontrol.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Comments

Michal Hocko March 16, 2020, 2:56 p.m. UTC | #1
On Thu 12-03-20 17:32:56, Chris Down wrote:
> This one is a bit more nuanced because we have memcg_max_mutex, which is
> mostly just used for enforcing invariants, but we still need to
> READ_ONCE since (despite its name) it doesn't really protect memory.max
> access.
> 
> On write (page_counter_set_max() and memory_max_write()) we use xchg(),
> which uses smp_mb(), so that's already fine.
> 
> Signed-off-by: Chris Down <chris@chrisdown.name>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Roman Gushchin <guro@fb.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: linux-mm@kvack.org
> Cc: cgroups@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: kernel-team@fb.com

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/memcontrol.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d32d3c0a16d4..aca2964ea494 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1507,7 +1507,7 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
>  
>  	pr_info("memory: usage %llukB, limit %llukB, failcnt %lu\n",
>  		K((u64)page_counter_read(&memcg->memory)),
> -		K((u64)memcg->memory.max), memcg->memory.failcnt);
> +		K((u64)READ_ONCE(memcg->memory.max)), memcg->memory.failcnt);
>  	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
>  		pr_info("swap: usage %llukB, limit %llukB, failcnt %lu\n",
>  			K((u64)page_counter_read(&memcg->swap)),
> @@ -1538,7 +1538,7 @@ unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
>  {
>  	unsigned long max;
>  
> -	max = memcg->memory.max;
> +	max = READ_ONCE(memcg->memory.max);
>  	if (mem_cgroup_swappiness(memcg)) {
>  		unsigned long memsw_max;
>  		unsigned long swap_max;
> @@ -3006,7 +3006,7 @@ static int mem_cgroup_resize_max(struct mem_cgroup *memcg,
>  		 * Make sure that the new limit (memsw or memory limit) doesn't
>  		 * break our basic invariant rule memory.max <= memsw.max.
>  		 */
> -		limits_invariant = memsw ? max >= memcg->memory.max :
> +		limits_invariant = memsw ? max >= READ_ONCE(memcg->memory.max) :
>  					   max <= memcg->memsw.max;
>  		if (!limits_invariant) {
>  			mutex_unlock(&memcg_max_mutex);
> @@ -3753,8 +3753,8 @@ static int memcg_stat_show(struct seq_file *m, void *v)
>  	/* Hierarchical information */
>  	memory = memsw = PAGE_COUNTER_MAX;
>  	for (mi = memcg; mi; mi = parent_mem_cgroup(mi)) {
> -		memory = min(memory, mi->memory.max);
> -		memsw = min(memsw, mi->memsw.max);
> +		memory = min(memory, READ_ONCE(mi->memory.max));
> +		memsw = min(memsw, READ_ONCE(mi->memsw.max));
>  	}
>  	seq_printf(m, "hierarchical_memory_limit %llu\n",
>  		   (u64)memory * PAGE_SIZE);
> @@ -4257,7 +4257,7 @@ void mem_cgroup_wb_stats(struct bdi_writeback *wb, unsigned long *pfilepages,
>  	*pheadroom = PAGE_COUNTER_MAX;
>  
>  	while ((parent = parent_mem_cgroup(memcg))) {
> -		unsigned long ceiling = min(memcg->memory.max,
> +		unsigned long ceiling = min(READ_ONCE(memcg->memory.max),
>  					    READ_ONCE(memcg->high));
>  		unsigned long used = page_counter_read(&memcg->memory);
>  
> -- 
> 2.25.1

Patch
diff mbox series

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d32d3c0a16d4..aca2964ea494 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1507,7 +1507,7 @@  void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
 
 	pr_info("memory: usage %llukB, limit %llukB, failcnt %lu\n",
 		K((u64)page_counter_read(&memcg->memory)),
-		K((u64)memcg->memory.max), memcg->memory.failcnt);
+		K((u64)READ_ONCE(memcg->memory.max)), memcg->memory.failcnt);
 	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
 		pr_info("swap: usage %llukB, limit %llukB, failcnt %lu\n",
 			K((u64)page_counter_read(&memcg->swap)),
@@ -1538,7 +1538,7 @@  unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
 {
 	unsigned long max;
 
-	max = memcg->memory.max;
+	max = READ_ONCE(memcg->memory.max);
 	if (mem_cgroup_swappiness(memcg)) {
 		unsigned long memsw_max;
 		unsigned long swap_max;
@@ -3006,7 +3006,7 @@  static int mem_cgroup_resize_max(struct mem_cgroup *memcg,
 		 * Make sure that the new limit (memsw or memory limit) doesn't
 		 * break our basic invariant rule memory.max <= memsw.max.
 		 */
-		limits_invariant = memsw ? max >= memcg->memory.max :
+		limits_invariant = memsw ? max >= READ_ONCE(memcg->memory.max) :
 					   max <= memcg->memsw.max;
 		if (!limits_invariant) {
 			mutex_unlock(&memcg_max_mutex);
@@ -3753,8 +3753,8 @@  static int memcg_stat_show(struct seq_file *m, void *v)
 	/* Hierarchical information */
 	memory = memsw = PAGE_COUNTER_MAX;
 	for (mi = memcg; mi; mi = parent_mem_cgroup(mi)) {
-		memory = min(memory, mi->memory.max);
-		memsw = min(memsw, mi->memsw.max);
+		memory = min(memory, READ_ONCE(mi->memory.max));
+		memsw = min(memsw, READ_ONCE(mi->memsw.max));
 	}
 	seq_printf(m, "hierarchical_memory_limit %llu\n",
 		   (u64)memory * PAGE_SIZE);
@@ -4257,7 +4257,7 @@  void mem_cgroup_wb_stats(struct bdi_writeback *wb, unsigned long *pfilepages,
 	*pheadroom = PAGE_COUNTER_MAX;
 
 	while ((parent = parent_mem_cgroup(memcg))) {
-		unsigned long ceiling = min(memcg->memory.max,
+		unsigned long ceiling = min(READ_ONCE(memcg->memory.max),
 					    READ_ONCE(memcg->high));
 		unsigned long used = page_counter_read(&memcg->memory);