From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Subject: mm/memcg: protect memcg_stock with a local_lock_t The members of the per-CPU structure memcg_stock_pcp are protected by disabling interrupts. This is not working on PREEMPT_RT because it creates atomic context in which actions are performed which require preemptible context. One example is obj_cgroup_release(). The IRQ-disable sections can be replaced with local_lock_t which preserves the explicit disabling of interrupts while keeps the code preemptible on PREEMPT_RT. drain_obj_stock() drops a reference on obj_cgroup which leads to an invocat= ion of obj_cgroup_release() if it is the last object. This in turn leads to recursive locking of the local_lock_t. To avoid this, obj_cgroup_release() = is invoked outside of the locked section. obj_cgroup_uncharge_pages() can be invoked with the local_lock_t acquired a= nd without it. This will lead later to a recursion in refill_stock(). To avoid the locking recursion provide obj_cgroup_uncharge_pages_locked() which uses the locked version of refill_stock(). - Replace disabling interrupts for memcg_stock with a local_lock_t. - Let drain_obj_stock() return the old struct obj_cgroup which is passed to obj_cgroup_put() outside of the locked section. - Provide obj_cgroup_uncharge_pages_locked() which uses the locked version of refill_stock() to avoid recursive locking in drain_obj_stock(). Link: https://lkml.kernel.org/r/20220209014709.GA26885@xsang-OptiPlex-9020 Link: https://lkml.kernel.org/r/20220226204144.1008339-6-bigeasy@xxxxxxxxxxxxx Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Michal Koutný <mkoutny@xxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Cc: Waiman Long <longman@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memcontrol.c | 59 +++++++++++++++++++++++++++++----------------- 1 file changed, 38 insertions(+), 21 deletions(-) --- a/mm/memcontrol.c~mm-memcg-protect-memcg_stock-with-a-local_lock_t +++ a/mm/memcontrol.c @@ -2135,6 +2135,7 @@ void unlock_page_memcg(struct page *page } struct memcg_stock_pcp { + local_lock_t stock_lock; struct mem_cgroup *cached; /* this never be root cgroup */ unsigned int nr_pages; @@ -2150,18 +2151,21 @@ struct memcg_stock_pcp { unsigned long flags; #define FLUSHING_CACHED_CHARGE 0 }; -static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock); +static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock) = { + .stock_lock = INIT_LOCAL_LOCK(stock_lock), +}; static DEFINE_MUTEX(percpu_charge_mutex); #ifdef CONFIG_MEMCG_KMEM -static void drain_obj_stock(struct memcg_stock_pcp *stock); +static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock); static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, struct mem_cgroup *root_memcg); static void memcg_account_kmem(struct mem_cgroup *memcg, int nr_pages); #else -static inline void drain_obj_stock(struct memcg_stock_pcp *stock) +static inline struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock) { + return NULL; } static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, struct mem_cgroup *root_memcg) @@ -2193,7 +2197,7 @@ static bool consume_stock(struct mem_cgr if (nr_pages > MEMCG_CHARGE_BATCH) return ret; - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.stock_lock, flags); stock = this_cpu_ptr(&memcg_stock); if (memcg == stock->cached && stock->nr_pages >= nr_pages) { @@ -2201,7 +2205,7 @@ static bool consume_stock(struct mem_cgr ret = true; } - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); return ret; } @@ -2230,6 +2234,7 @@ static void drain_stock(struct memcg_sto static void drain_local_stock(struct work_struct *dummy) { struct memcg_stock_pcp *stock; + struct obj_cgroup *old = NULL; unsigned long flags; /* @@ -2237,14 +2242,16 @@ static void drain_local_stock(struct wor * drain_stock races is that we always operate on local CPU stock * here with IRQ disabled */ - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.stock_lock, flags); stock = this_cpu_ptr(&memcg_stock); - drain_obj_stock(stock); + old = drain_obj_stock(stock); drain_stock(stock); clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); + if (old) + obj_cgroup_put(old); } /* @@ -2271,9 +2278,9 @@ static void refill_stock(struct mem_cgro { unsigned long flags; - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.stock_lock, flags); __refill_stock(memcg, nr_pages); - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); } /* @@ -3100,10 +3107,11 @@ void mod_objcg_state(struct obj_cgroup * enum node_stat_item idx, int nr) { struct memcg_stock_pcp *stock; + struct obj_cgroup *old = NULL; unsigned long flags; int *bytes; - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.stock_lock, flags); stock = this_cpu_ptr(&memcg_stock); /* @@ -3112,7 +3120,7 @@ void mod_objcg_state(struct obj_cgroup * * changes. */ if (stock->cached_objcg != objcg) { - drain_obj_stock(stock); + old = 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; @@ -3156,7 +3164,9 @@ void mod_objcg_state(struct obj_cgroup * if (nr) mod_objcg_mlstate(objcg, pgdat, idx, nr); - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); + if (old) + obj_cgroup_put(old); } static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes) @@ -3165,7 +3175,7 @@ static bool consume_obj_stock(struct obj unsigned long flags; bool ret = false; - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.stock_lock, flags); stock = this_cpu_ptr(&memcg_stock); if (objcg == stock->cached_objcg && stock->nr_bytes >= nr_bytes) { @@ -3173,17 +3183,17 @@ static bool consume_obj_stock(struct obj ret = true; } - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); return ret; } -static void drain_obj_stock(struct memcg_stock_pcp *stock) +static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock) { struct obj_cgroup *old = stock->cached_objcg; if (!old) - return; + return NULL; if (stock->nr_bytes) { unsigned int nr_pages = stock->nr_bytes >> PAGE_SHIFT; @@ -3233,8 +3243,12 @@ static void drain_obj_stock(struct memcg stock->cached_pgdat = NULL; } - obj_cgroup_put(old); 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; } static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, @@ -3255,14 +3269,15 @@ static void refill_obj_stock(struct obj_ bool allow_uncharge) { struct memcg_stock_pcp *stock; + struct obj_cgroup *old = NULL; unsigned long flags; unsigned int nr_pages = 0; - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.stock_lock, flags); stock = this_cpu_ptr(&memcg_stock); if (stock->cached_objcg != objcg) { /* reset if necessary */ - drain_obj_stock(stock); + old = drain_obj_stock(stock); obj_cgroup_get(objcg); stock->cached_objcg = objcg; stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes) @@ -3276,7 +3291,9 @@ static void refill_obj_stock(struct obj_ stock->nr_bytes &= (PAGE_SIZE - 1); } - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); + if (old) + obj_cgroup_put(old); if (nr_pages) obj_cgroup_uncharge_pages(objcg, nr_pages); _
