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[94.245.46.49]) by smtp.gmail.com with ESMTPSA id c17sm9529603lfr.23.2020.08.09.13.44.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 09 Aug 2020 13:44:05 -0700 (PDT) From: "Uladzislau Rezki (Sony)" To: LKML , RCU , linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , "Paul E . McKenney" , Matthew Wilcox Cc: "Theodore Y . Ts'o" , Joel Fernandes , Sebastian Andrzej Siewior , Uladzislau Rezki , Oleksiy Avramchenko Subject: [PATCH 2/2] rcu/tree: use __GFP_NO_LOCKS flag Date: Sun, 9 Aug 2020 22:43:54 +0200 Message-Id: <20200809204354.20137-3-urezki@gmail.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200809204354.20137-1-urezki@gmail.com> References: <20200809204354.20137-1-urezki@gmail.com> MIME-Version: 1.0 X-Rspamd-Queue-Id: A65743D663 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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: Enter the page allocator with newly introduced __GFP_NO_LOCKS flag instead of former GFP_NOWAIT | __GFP_NOWARN sequence. Such approach address two concerns. See them below: a) If built with CONFIG_PROVE_RAW_LOCK_NESTING, the lockdep complains about violation("BUG: Invalid wait context") of the nesting rules. It does the raw_spinlock vs. spinlock nesting checks, i.e. it is not legal to acquire a spinlock_t while holding a raw_spinlock_t. Internally the kfree_rcu() uses raw_spinlock_t whereas the page allocator internally deals with spinlock_t to access to its zones. The code also can be broken from higher level of view: raw_spin_lock(&some_lock); kfree_rcu(some_pointer, some_field_offset); b) If built with CONFIG_PREEMPT_RT. Please note, in that case spinlock_t is converted into sleepable variant. Invoking the page allocator from atomic contexts leads to: "BUG: scheduling while atomic". Signed-off-by: Uladzislau Rezki (Sony) --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 30e7e252b9e7..48cb64800108 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3327,7 +3327,7 @@ kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp, void *ptr) * pages are available. */ bnode = (struct kvfree_rcu_bulk_data *) - __get_free_page(GFP_NOWAIT | __GFP_NOWARN); + __get_free_page(__GFP_NO_LOCKS); } /* Switch to emergency path. */