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[94.245.46.49]) by smtp.gmail.com with ESMTPSA id u27sm586992ljd.79.2020.07.15.11.35.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jul 2020 11:35:44 -0700 (PDT) From: "Uladzislau Rezki (Sony)" To: LKML , RCU , linux-mm@kvack.org, "Paul E . McKenney" Cc: Andrew Morton , "Theodore Y . Ts'o" , Matthew Wilcox , Joel Fernandes , Sebastian Andrzej Siewior , Uladzislau Rezki , Oleksiy Avramchenko Subject: [PATCH 1/1] rcu/tree: Drop the lock before entering to page allocator Date: Wed, 15 Jul 2020 20:35:37 +0200 Message-Id: <20200715183537.4010-1-urezki@gmail.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 X-Rspamd-Queue-Id: D24721819E764 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: If the kernel is built with CONFIG_PROVE_RAW_LOCK_NESTING option, the lockedp will complain about violation of the nesting rules. It does the raw_spinlock vs. spinlock nesting checks. Internally the kfree_rcu() uses raw_spinlock_t whereas the page allocator internally deals with spinlock_t to access to its zones. In order to prevent such vialation that is in question we can drop the internal raw_spinlock_t before entering to the page allocaor. Signed-off-by: Uladzislau Rezki (Sony) --- kernel/rcu/tree.c | 36 +++++++++++++++++++----------------- 1 file changed, 19 insertions(+), 17 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 21c2fa5bd8c3..7469bd1e5c2c 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3278,21 +3278,22 @@ static void kfree_rcu_monitor(struct work_struct = *work) } =20 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) { struct kvfree_rcu_bulk_data *bnode; int idx; =20 - if (unlikely(!krcp->initialized)) + *krcp =3D krc_this_cpu_lock(flags); + if (unlikely(!(*krcp)->initialized)) return false; =20 - lockdep_assert_held(&krcp->lock); idx =3D !!is_vmalloc_addr(ptr); =20 /* Check if a new block is required. */ - if (!krcp->bkvhead[idx] || - krcp->bkvhead[idx]->nr_records =3D=3D KVFREE_BULK_MAX_ENTR) { - bnode =3D get_cached_bnode(krcp); + if (!(*krcp)->bkvhead[idx] || + (*krcp)->bkvhead[idx]->nr_records =3D=3D KVFREE_BULK_MAX_ENTR) { + bnode =3D get_cached_bnode(*krcp); if (!bnode) { /* * To keep this path working on raw non-preemptible @@ -3306,6 +3307,9 @@ kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cp= u *krcp, void *ptr) if (IS_ENABLED(CONFIG_PREEMPT_RT)) return false; =20 + preempt_disable(); + krc_this_cpu_unlock(*krcp, *flags); + /* * NOTE: For one argument of kvfree_rcu() we can * drop the lock and get the page in sleepable @@ -3315,6 +3319,9 @@ kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cp= u *krcp, void *ptr) */ bnode =3D (struct kvfree_rcu_bulk_data *) __get_free_page(GFP_NOWAIT | __GFP_NOWARN); + + *krcp =3D krc_this_cpu_lock(flags); + preempt_enable(); } =20 /* Switch to emergency path. */ @@ -3323,15 +3330,15 @@ kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_= cpu *krcp, void *ptr) =20 /* Initialize the new block. */ bnode->nr_records =3D 0; - bnode->next =3D krcp->bkvhead[idx]; + bnode->next =3D (*krcp)->bkvhead[idx]; =20 /* Attach it to the head. */ - krcp->bkvhead[idx] =3D bnode; + (*krcp)->bkvhead[idx] =3D bnode; } =20 /* Finally insert. */ - krcp->bkvhead[idx]->records - [krcp->bkvhead[idx]->nr_records++] =3D ptr; + (*krcp)->bkvhead[idx]->records + [(*krcp)->bkvhead[idx]->nr_records++] =3D ptr; =20 return true; } @@ -3369,24 +3376,19 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_c= allback_t func) ptr =3D (unsigned long *) func; } =20 - krcp =3D 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 =3D true; - goto unlock_return; + return; } =20 /* * Under high memory pressure GFP_NOWAIT can fail, * in that case the emergency path is maintained. */ - success =3D kvfree_call_rcu_add_ptr_to_bulk(krcp, ptr); + success =3D add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr); if (!success) { if (head =3D=3D NULL) // Inline if kvfree_rcu(one_arg) call. --=20 2.20.1