Given that CONFIG_PREEMPT_COUNT is unconditionally enabled by the earlier commits in this series, the preemptible() macro now properly detects preempt-disable code regions even in kernels built with CONFIG_PREEMPT_NONE.
This commit therefore uses preemptible() to determine whether allocation is possible at all for double-argument kvfree_rcu(). If !preemptible(), then allocation is not possible, and kvfree_rcu() falls back to using the less cache-friendly rcu_head approach. Even when preemptible(), the caller might be involved in reclaim, so the GFP_ flags used by double-argument kvfree_rcu() must avoid invoking reclaim processing. Note that single-argument kvfree_rcu() must be invoked in sleepable contexts, and that its fallback is the relatively high latency synchronize_rcu(). Single-argument kvfree_rcu() therefore uses GFP_KERNEL|__GFP_RETRY_MAYFAIL to allow limited sleeping within the memory allocator. [ paulmck: Add add_ptr_to_bulk_krc_lock header comment per Michal Hocko. ] Signed-off-by: Uladzislau Rezki (Sony) <[email protected]> Signed-off-by: Paul E. McKenney <[email protected]> --- kernel/rcu/tree.c | 48 ++++++++++++++++++++++++++++++----------------- 1 file changed, 31 insertions(+), 17 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index f2da2a1cc716..3f9b016a44dc 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3406,37 +3406,55 @@ run_page_cache_worker(struct kfree_rcu_cpu *krcp) } } +// Record ptr in a page managed by krcp, with the pre-krc_this_cpu_lock() +// state specified by flags. If can_sleep is true, the caller must +// be schedulable and not be holding any locks or mutexes that might be +// acquired by the memory allocator or anything that it might invoke. +// If !can_sleep, then if !preemptible() no allocation will be undertaken, +// otherwise the allocation will use GFP_ATOMIC to avoid the remainder of +// the aforementioned deadlock possibilities. Returns true if ptr was +// successfully recorded, else the caller must use a fallback. static inline bool -kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp, void *ptr) +add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp, + unsigned long *flags, void *ptr, bool can_sleep) { struct kvfree_rcu_bulk_data *bnode; + bool can_alloc_page = preemptible(); + gfp_t gfp = (can_sleep ? GFP_KERNEL | __GFP_RETRY_MAYFAIL : + GFP_ATOMIC) | __GFP_NOWARN; int idx; - if (unlikely(!krcp->initialized)) + *krcp = krc_this_cpu_lock(flags); + if (unlikely(!(*krcp)->initialized)) return false; - lockdep_assert_held(&krcp->lock); idx = !!is_vmalloc_addr(ptr); /* Check if a new block is required. */ - if (!krcp->bkvhead[idx] || - krcp->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) { - bnode = get_cached_bnode(krcp); - /* Switch to emergency path. */ + if (!(*krcp)->bkvhead[idx] || + (*krcp)->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) { + bnode = get_cached_bnode(*krcp); + if (!bnode && can_alloc_page) { + krc_this_cpu_unlock(*krcp, *flags); + bnode = (struct kvfree_rcu_bulk_data *) + __get_free_page(gfp); + *krcp = krc_this_cpu_lock(flags); + } + if (!bnode) return false; /* Initialize the new block. */ bnode->nr_records = 0; - bnode->next = krcp->bkvhead[idx]; + bnode->next = (*krcp)->bkvhead[idx]; /* Attach it to the head. */ - krcp->bkvhead[idx] = bnode; + (*krcp)->bkvhead[idx] = bnode; } /* Finally insert. */ - krcp->bkvhead[idx]->records - [krcp->bkvhead[idx]->nr_records++] = ptr; + (*krcp)->bkvhead[idx]->records + [(*krcp)->bkvhead[idx]->nr_records++] = ptr; return true; } @@ -3474,20 +3492,16 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) ptr = (unsigned long *) func; } - krcp = krc_this_cpu_lock(&flags); - // Queue the object but don't yet schedule the batch. if (debug_rcu_head_queue(ptr)) { // Probable double kfree_rcu(), just leak. WARN_ONCE(1, "%s(): Double-freed call. rcu_head %p\n", __func__, head); - // Mark as success and leave. - success = true; - goto unlock_return; + return; } - success = kvfree_call_rcu_add_ptr_to_bulk(krcp, ptr); + success = add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr, !head); if (!success) { run_page_cache_worker(krcp); -- 2.20.1
