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Wed, 24 Jun 2026 13:41:23 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id FeK3BIPeO2q0FQAAD6G6ig (envelope-from ); Wed, 24 Jun 2026 13:41:23 +0000 Date: Wed, 24 Jun 2026 14:41:20 +0100 From: Pedro Falcato To: "Harry Yoo (Oracle)" Cc: Vlastimil Babka , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Alexei Starovoitov , Andrii Nakryiko , Puranjay Mohan , Amery Hung , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Suren Baghdasaryan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, rcu@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH for-next v3 2/9] mm/slab, slub_kunit: register kprobe to trigger _nolock APIs Message-ID: References: <20260615-kfree_rcu_nolock-v3-0-70a54f3775bb@kernel.org> <20260615-kfree_rcu_nolock-v3-2-70a54f3775bb@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260615-kfree_rcu_nolock-v3-2-70a54f3775bb@kernel.org> X-Spam-Flag: NO X-Spam-Score: -3.80 X-Spamd-Result: default: False [-3.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_RHS_NOT_FQDN(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; TO_DN_SOME(0.00)[]; MISSING_XM_UA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[30]; FUZZY_RATELIMITED(0.00)[rspamd.com]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; R_RATELIMIT(0.00)[to_ip_from(RLg9nrgqsibwm9ympc34uc4grz)]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[kernel.org,linux-foundation.org,linux.dev,gentwo.org,google.com,gmail.com,linutronix.de,goodmis.org,nvidia.com,joshtriplett.org,efficios.com,kvack.org,vger.kernel.org,lists.linux.dev]; RCVD_TLS_ALL(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] X-Spam-Level: On Mon, Jun 15, 2026 at 08:05:56PM +0900, Harry Yoo (Oracle) wrote: > Since kmalloc_nolock() always fails in NMI and hardirq contexts on > PREEMPT_RT, slub_kunit cannot properly test _nolock() APIs. > > Register a kprobe pre-handler to invoke kmalloc_nolock() and > kfree_nolock() in the middle of the slab allocator. However, do not > register the handler on UP kernels [1]. Maybe explain in the commit message why that is? > To attach the pre-handler while s->cpu_sheaves->lock or n->list_lock > is held, add a wrapper function for lockdep_assert_held() that calls > a no-op function slab_attach_kprobe_locked() on debug builds. The Why lockdep? Wouldn't it make more sense to add these triggers after locking these locks? > function is optimized away when neither CONFIG_PROVE_LOCKING nor > CONFIG_DEBUG_VM is selected and register_kprobe() fails. > > The function calls barrier() to prevent the compiler from optimizing > away its callsites. Otherwise, the compiler may consider the function > does not have any side effect and remove callsites. My wider comment is the following: this looks very useful but perhaps should be lifted to Kunit itself? There's already function redirection (which could be used for this as well). I don't know if that suits your purposes? Choosing to say "I want to hook this random function using kprobe and give it custom behavior" sounds lovely for all sorts of testing. -- Pedro