From: Shakeel Butt Date: Fri, 4 Apr 2025 01:39:10 +0000 (-0700) Subject: memcg: do obj_cgroup_put inside drain_obj_stock X-Git-Tag: v6.16-rc1~92^2~244 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ae51c775aa2b1fd4fbaf781740ec8762292bec3a;p=thirdparty%2Fkernel%2Fstable.git memcg: do obj_cgroup_put inside drain_obj_stock Previously we could not call obj_cgroup_put() inside the local lock because on the put on the last reference, the release function obj_cgroup_release() may try to re-acquire the local lock. However that chain has been broken. Now simply do obj_cgroup_put() inside drain_obj_stock() instead of returning the old objcg. Link: https://lkml.kernel.org/r/20250404013913.1663035-7-shakeel.butt@linux.dev Signed-off-by: Shakeel Butt Reviewed-by: Roman Gushchin Acked-by: Vlastimil Babka Cc: Johannes Weiner Cc: Michal Hocko Cc: Muchun Song Cc: Sebastian Andrzej Siewior Signed-off-by: Andrew Morton --- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index df52084e90f46..7988a42b29bfc 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1785,7 +1785,7 @@ static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock) = { }; static DEFINE_MUTEX(percpu_charge_mutex); -static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock); +static void drain_obj_stock(struct memcg_stock_pcp *stock); static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, struct mem_cgroup *root_memcg); @@ -1859,7 +1859,6 @@ static void drain_stock(struct memcg_stock_pcp *stock) static void drain_local_stock(struct work_struct *dummy) { struct memcg_stock_pcp *stock; - struct obj_cgroup *old = NULL; unsigned long flags; /* @@ -1870,12 +1869,11 @@ static void drain_local_stock(struct work_struct *dummy) local_lock_irqsave(&memcg_stock.stock_lock, flags); stock = this_cpu_ptr(&memcg_stock); - old = drain_obj_stock(stock); + drain_obj_stock(stock); drain_stock(stock); clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); local_unlock_irqrestore(&memcg_stock.stock_lock, flags); - obj_cgroup_put(old); } static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) @@ -1958,18 +1956,16 @@ void drain_all_stock(struct mem_cgroup *root_memcg) static int memcg_hotplug_cpu_dead(unsigned int cpu) { struct memcg_stock_pcp *stock; - struct obj_cgroup *old; unsigned long flags; stock = &per_cpu(memcg_stock, cpu); /* drain_obj_stock requires stock_lock */ local_lock_irqsave(&memcg_stock.stock_lock, flags); - old = drain_obj_stock(stock); + drain_obj_stock(stock); local_unlock_irqrestore(&memcg_stock.stock_lock, flags); drain_stock(stock); - obj_cgroup_put(old); return 0; } @@ -2766,24 +2762,20 @@ void __memcg_kmem_uncharge_page(struct page *page, int order) } /* Replace the stock objcg with objcg, return the old objcg */ -static struct obj_cgroup *replace_stock_objcg(struct memcg_stock_pcp *stock, - struct obj_cgroup *objcg) +static void replace_stock_objcg(struct memcg_stock_pcp *stock, + struct obj_cgroup *objcg) { - struct obj_cgroup *old = NULL; - - old = drain_obj_stock(stock); + drain_obj_stock(stock); obj_cgroup_get(objcg); stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes) ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0; WRITE_ONCE(stock->cached_objcg, objcg); - return old; } static void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat, enum node_stat_item idx, int nr) { struct memcg_stock_pcp *stock; - struct obj_cgroup *old = NULL; unsigned long flags; int *bytes; @@ -2796,7 +2788,7 @@ static void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat, * changes. */ if (READ_ONCE(stock->cached_objcg) != objcg) { - old = replace_stock_objcg(stock, objcg); + replace_stock_objcg(stock, objcg); stock->cached_pgdat = pgdat; } else if (stock->cached_pgdat != pgdat) { /* Flush the existing cached vmstat data */ @@ -2837,7 +2829,6 @@ static void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat, __mod_objcg_mlstate(objcg, pgdat, idx, nr); local_unlock_irqrestore(&memcg_stock.stock_lock, flags); - obj_cgroup_put(old); } static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes) @@ -2859,12 +2850,12 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes) return ret; } -static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock) +static void drain_obj_stock(struct memcg_stock_pcp *stock) { struct obj_cgroup *old = READ_ONCE(stock->cached_objcg); if (!old) - return NULL; + return; if (stock->nr_bytes) { unsigned int nr_pages = stock->nr_bytes >> PAGE_SHIFT; @@ -2917,11 +2908,7 @@ static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock) } WRITE_ONCE(stock->cached_objcg, NULL); - /* - * The `old' objects needs to be released by the caller via - * obj_cgroup_put() outside of memcg_stock_pcp::stock_lock. - */ - return old; + obj_cgroup_put(old); } static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, @@ -2943,7 +2930,6 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, bool allow_uncharge) { struct memcg_stock_pcp *stock; - struct obj_cgroup *old = NULL; unsigned long flags; unsigned int nr_pages = 0; @@ -2951,7 +2937,7 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, stock = this_cpu_ptr(&memcg_stock); if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */ - old = replace_stock_objcg(stock, objcg); + replace_stock_objcg(stock, objcg); allow_uncharge = true; /* Allow uncharge when objcg changes */ } stock->nr_bytes += nr_bytes; @@ -2962,7 +2948,6 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, } local_unlock_irqrestore(&memcg_stock.stock_lock, flags); - obj_cgroup_put(old); if (nr_pages) obj_cgroup_uncharge_pages(objcg, nr_pages);