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[37.188.158.19]) by smtp.gmail.com with ESMTPSA id y62sm12010608edy.61.2020.06.17.04.31.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Jun 2020 04:31:59 -0700 (PDT) Date: Wed, 17 Jun 2020 13:31:57 +0200 From: Michal Hocko To: Matthew Wilcox Cc: dsterba@suse.cz, Joe Perches , Waiman Long , Andrew Morton , David Howells , Jarkko Sakkinen , James Morris , "Serge E. Hallyn" , Linus Torvalds , David Rientjes , Johannes Weiner , Dan Carpenter , "Jason A . Donenfeld" , linux-mm@kvack.org, keyrings@vger.kernel.org, linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, linux-pm@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-amlogic@lists.infradead.org, linux-mediatek@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-ppp@vger.kernel.org, wireguard@lists.zx2c4.com, linux-wireless@vger.kernel.org, devel@driverdev.osuosl.org, linux-scsi@vger.kernel.org, target-devel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-cifs@vger.kernel.org, linux-fscrypt@vger.kernel.org, ecryptfs@vger.kernel.org, kasan-dev@googlegroups.com, linux-bluetooth@vger.kernel.org, linux-wpan@vger.kernel.org, linux-sctp@vger.kernel.org, linux-nfs@vger.kernel.org, tipc-discussion@lists.sourceforge.net, linux-security-module@vger.kernel.org, linux-integrity@vger.kernel.org Subject: Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive() Message-ID: <20200617113157.GM9499@dhcp22.suse.cz> References: <20200616015718.7812-1-longman@redhat.com> <20200616230130.GJ27795@twin.jikos.cz> <20200617003711.GD8681@bombadil.infradead.org> <20200617071212.GJ9499@dhcp22.suse.cz> <20200617110820.GG8681@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200617110820.GG8681@bombadil.infradead.org> X-Rspamd-Queue-Id: EB11D180C07A3 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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: On Wed 17-06-20 04:08:20, Matthew Wilcox wrote: > On Wed, Jun 17, 2020 at 09:12:12AM +0200, Michal Hocko wrote: > > On Tue 16-06-20 17:37:11, Matthew Wilcox wrote: > > > Not just performance critical, but correctness critical. Since kvfree() > > > may allocate from the vmalloc allocator, I really think that kvfree() > > > should assert that it's !in_atomic(). Otherwise we can get into trouble > > > if we end up calling vfree() and have to take the mutex. > > > > FWIW __vfree already checks for atomic context and put the work into a > > deferred context. So this should be safe. It should be used as a last > > resort, though. > > Actually, it only checks for in_interrupt(). You are right. I have misremembered. You have made me look (thanks) ... > If you call vfree() under > a spinlock, you're in trouble. in_atomic() only knows if we hold a > spinlock for CONFIG_PREEMPT, so it's not safe to check for in_atomic() > in __vfree(). So we need the warning in order that preempt people can > tell those without that there is a bug here. ... Unless I am missing something in_interrupt depends on preempt_count() as well so neither of the two is reliable without PREEMPT_COUNT configured. -- Michal Hocko SUSE Labs