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Wed, 29 Jul 2020 16:32:47 -0700 (PDT) Date: Wed, 29 Jul 2020 16:32:46 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: "Zhang, Qiang" cc: "cl@linux.com" , "penberg@kernel.org" , "iamjoonsoo.kim@lge.com" , "akpm@linux-foundation.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: =?UTF-8?Q?Re=3A_=E5=9B=9E=E5=A4=8D=3A_=5BPATCH=5D_mm=2Fslab=2Ec=3A?= =?UTF-8?Q?_add_node_spinlock_protect_in_=5F=5Fcache=5Ffree=5F?= =?UTF-8?Q?alien?= In-Reply-To: Message-ID: References: <20200728095551.30634-1-qiang.zhang@windriver.com>, User-Agent: Alpine 2.23 (DEB 453 2020-06-18) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: EAB8A180442CB 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: On Wed, 29 Jul 2020, Zhang, Qiang wrote: > > From: Zhang Qiang > > > > We should add node spinlock protect "n->alien" which may be > > assigned to NULL in cpuup_canceled func. cause address access > > exception. > > > > >Hi, do you have an example NULL pointer dereference where you have hit > >this? > If you have a NULL pointer dereference or a GPF that occurred because of this, it would be helpful to provide as rationale. > >This rather looks like something to fix up in cpuup_canceled() since it's > >currently manipulating the alien cache for the canceled cpu's node. > > yes , it is fix up in cpuup_canceled it's > currently manipulating the alien cache for the canceled cpu's node which may be the same as the node being operated on in the __cache_free_alien func. > > void cpuup_canceled > { > n = get_node(cachep, node); > spin_lock_irq(&n->list_lock); > ... > n->alien = NULL; > spin_unlock_irq(&n->list_lock); > .... > } > Right, so the idea is that this should be fixed in cpuup_canceled() instead -- why would we invaliate the entire node's alien cache because a single cpu failed to come online?