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Peter Anvin" , Andrew Morton , Dave Chinner , Qi Zheng , Roman Gushchin , Muchun Song , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Uladzislau Rezki , David Hildenbrand , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Sebastian Andrzej Siewior , Clark Williams , suleiman@google.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-rt-devel@lists.linux.dev Subject: Re: [RFC 06/10] Reclaim memory from blocked kernel stacks Message-ID: <20260828125706.GQ687043@noisy.programming.kicks-ass.net> References: <20260827232948.2520558-1-stevensd@google.com> <20260827232948.2520558-7-stevensd@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260827232948.2520558-7-stevensd@google.com> X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 83C441C0007 X-Stat-Signature: ekh7mujronq6qiiwmohmed1kggtmq5g4 X-HE-Tag: 1787921836-491681 X-HE-Meta: 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 yTndrKiD kckAVt/XYYOKgO4GayfkRd5nh9gYYVZEyh7szL/IacXm48qG+2xPrcbtmdJb+9qXwPpnDEiLD8RKvlzoQuDCPUzDCLb1jDsJtePEYr16bK85VkjoigBiNFGtfBIuEIU3IVDxF6RiQ9yEoNEGvb+jHLs24HNfGUqgbURXZudhwcaob3Lo4YvR61rLkBrJnPd84u3+PLSNN/BOB+jI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 27, 2026 at 04:29:44PM -0700, David Stevens wrote: > +DEFINE_CLASS(allow_stack_reclaim, bool, > + ({ > + if (!_T) > + current->flags &= ~PF_RECLAIMABLE_STACK; > + }), > + ({ > + bool was_set = current->flags & PF_RECLAIMABLE_STACK; > + > + current->flags |= PF_RECLAIMABLE_STACK; > + was_set; > + }), > + void) > + allow_stack_reclaim(prev); > +void __allow_stack_reclaim(struct task_struct *tsk) > +{ > + union stack_reclaim_state prev_state, target_state; > + > + if (WARN_ON_ONCE(tsk->__state == TASK_DEAD)) > + return; > + > + prev_state.val = READ_ONCE(tsk->stack_reclaim_state.val); > + do { > + target_state.val = prev_state.val; > + > + if (prev_state.stack_state != STACK_PREPARE_RECLAIM) { > + WARN(prev_state.stack_state != STACK_IN_USE, > + "Reclaimable state %x for previously running task", prev_state.val); > + return; > + } > + target_state.stack_state = STACK_RECLAIMABLE; > + } while (!try_cmpxchg(&tsk->stack_reclaim_state.val, &prev_state.val, target_state.val)); > + > + if (irq_work_queue(&tsk->stack_reclaim_work->irq_work)) { > + /* > + * Take a ref that gets released by do_reclaim_stack() so we don't > + * have to worry about races with remove_from_stack_shrinker(). > + */ > + get_task_struct(tsk); > + } > +} > +static inline void allow_stack_reclaim(struct task_struct *tsk) > +{ > + if (unlikely(tsk->flags & PF_RECLAIMABLE_STACK)) > + __allow_stack_reclaim(tsk); > +} So you have a guard with the same name as a function, but the function only functions when inside the guard of the same name. WTF ?! Anyway, it looks like you're sprinkling this guard around a few specific block sites. Which seems to suggest your PF_ flag *should* have been a TASK_ flag, no?