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McKenney" To: Sebastian Andrzej Siewior Cc: Boqun Feng , Vlastimil Babka , Marco Elver , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, sfr@canb.auug.org.au, longman@redhat.com, cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, Tomas Gleixner , Peter Zijlstra Subject: Re: [PATCH 2/2] scftorture: Use a lock-less list to free memory. Message-ID: <45725c86-d07f-4422-a6fd-c9f02744ac75@paulmck-laptop> Reply-To: paulmck@kernel.org References: <88694240-1eea-4f4c-bb7b-80de25f252e7@paulmck-laptop> <20241104105053.2182833-1-bigeasy@linutronix.de> <20241104105053.2182833-2-bigeasy@linutronix.de> <20241107112107.3rO2RTzX@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20241107112107.3rO2RTzX@linutronix.de> X-Rspam-User: X-Rspamd-Queue-Id: 87DB740002 X-Rspamd-Server: rspam11 X-Stat-Signature: 9uwuiifp7rya578yxgbp3nzz7dbti9n4 X-HE-Tag: 1730988489-344805 X-HE-Meta: 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 Zs5dlLsC 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 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: List-Subscribe: List-Unsubscribe: On Thu, Nov 07, 2024 at 12:21:07PM +0100, Sebastian Andrzej Siewior wrote: > On 2024-11-04 17:00:19 [-0800], Boqun Feng wrote: > > Hi Sebastian, > Hi Boqun, > > … > > I think this needs to be: > > > > scf_cleanup_free_list(cpu); > > > > or > > > > scf_cleanup_free_list(curcpu); > > > > because scfp->cpu is actually the thread number, and I got a NULL > > dereference: > > > > [ 14.219225] BUG: unable to handle page fault for address: ffffffffb2ff7210 > > Right. Replaced with cpu. > … > > > > Another thing is, how do we guarantee that we don't exit the loop > > eariler (i.e. while there are still callbacks on the list)? After the > > following scftorture_invoke_one(), there could an IPI pending somewhere, > > and we may exit this loop if torture_must_stop() is true. And that IPI > > might add its scf_check to the list but no scf_cleanup_free_list() is > > going to handle that, right? > > Okay. Assuming that IPIs are done by the time scf_torture_cleanup is > invoked, I added scf_cleanup_free_list() for all CPUs there. This statement in scf_torture_cleanup() is supposed to wait for all outstanding IPIs: smp_call_function(scf_cleanup_handler, NULL, 0); And the scf_cleanup_handler() function is as follows: static void scf_cleanup_handler(void *unused) { } Does that work, or am I yet again being overly naive? > Reposted at > https://lore.kernel.org/20241107111821.3417762-1-bigeasy@linutronix.de Thank you! I will do some testing on this later today. Thanx, Paul