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Ts'o" , Joel Fernandes , Sebastian Andrzej Siewior , Oleksiy Avramchenko Subject: Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag In-Reply-To: <20200811153327.GW4295@paulmck-ThinkPad-P72> References: <20200809204354.20137-1-urezki@gmail.com> <20200809204354.20137-2-urezki@gmail.com> <20200810123141.GF4773@dhcp22.suse.cz> <20200810160739.GA29884@pc636> <20200810192525.GG4773@dhcp22.suse.cz> <87pn7x6y4a.fsf@nanos.tec.linutronix.de> <20200811153327.GW4295@paulmck-ThinkPad-P72> Date: Tue, 11 Aug 2020 17:43:16 +0200 Message-ID: <87h7t96ve3.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: 08FC218229837 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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: "Paul E. McKenney" writes: > On Tue, Aug 11, 2020 at 04:44:21PM +0200, Thomas Gleixner wrote: >> Now RCU creates a new thing which enforces to make page allocation in >> atomic context possible on RT. What for? >> >> What's the actual use case in truly atomic context for this new thing on >> an RT kernel? > > It is not just RT kernels. CONFIG_PROVE_RAW_LOCK_NESTING=y propagates > this constraint to all configurations, and a patch in your new favorite > subsystem really did trigger this lockdep check in a non-RT kernel. > >> The actual RCU code disabling interrupts is an implementation detail >> which can easily be mitigated with a local lock. > > In this case, we are in raw-spinlock context on entry to kfree_rcu(). Where?