From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> 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 invocation 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 and 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 Reported-by: kernel test robot <oliver.sang@xxxxxxxxx> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> [do: backported to v5.15] Signed-off-by: David Oberhollenzer <goliath@xxxxxxxxxxxx> --- mm/memcontrol.c | 55 ++++++++++++++++++++++++++++++------------------- 1 file changed, 34 insertions(+), 21 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 2cf55b3ab4b0..20bce9682e8a 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2152,6 +2152,7 @@ void unlock_page_memcg(struct page *page) EXPORT_SYMBOL(unlock_page_memcg); struct memcg_stock_pcp { + local_lock_t stock_lock; struct mem_cgroup *cached; /* this never be root cgroup */ unsigned int nr_pages; @@ -2167,17 +2168,20 @@ 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); #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) @@ -2206,7 +2210,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) 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) { @@ -2214,7 +2218,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) ret = true; } - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); return ret; } @@ -2243,6 +2247,7 @@ 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; /* @@ -2250,14 +2255,16 @@ static void drain_local_stock(struct work_struct *dummy) * 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); } /* @@ -2284,9 +2291,9 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) { 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); } /* @@ -3095,10 +3102,11 @@ 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; - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.stock_lock, flags); stock = this_cpu_ptr(&memcg_stock); /* @@ -3107,7 +3115,7 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat, * 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; @@ -3151,7 +3159,9 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat, 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) @@ -3160,7 +3170,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes) 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) { @@ -3168,17 +3178,17 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes) 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; @@ -3230,8 +3240,8 @@ static void drain_obj_stock(struct memcg_stock_pcp *stock) stock->cached_pgdat = NULL; } - obj_cgroup_put(old); stock->cached_objcg = NULL; + return old; } static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, @@ -3252,14 +3262,15 @@ 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; - 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) @@ -3273,7 +3284,9 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, 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); -- 2.37.1
