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Wed, 20 May 2026 13:44:44 +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 kmDJJMy6DWrXUAAAD6G6ig (envelope-from ); Wed, 20 May 2026 13:44:44 +0000 From: Gabriel Krisman Bertazi To: "Fengnan Chang" Cc: , , , , Subject: Re: [PATCH] io_uring/io-wq: avoid repeated task_work scans during teardown In-Reply-To: <20260520031221.83210-1-changfengnan@bytedance.com> (Fengnan Chang's message of "Wed, 20 May 2026 11:12:21 +0800") References: <20260520031221.83210-1-changfengnan@bytedance.com> Date: Wed, 20 May 2026 15:44:36 +0200 Message-ID: <87wlwynqkb.fsf@mailhost.krisman.be> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-Spam-Level: X-Rspamd-Action: no action X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_FIVE(0.00)[6]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim,imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:106:10:150:64:167:received]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Queue-Id: 9FCFD67C46 X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spam-Flag: NO X-Spam-Score: -4.51 "Fengnan Chang" writes: > We hit hard-lockup reports from iou-wrk threads stuck in It seems like a soft-lockup instead no? From your description, eventually it solves itself, the task is just uninterruptible while contending on the spinlock. > + */ > +struct callback_head * > +task_work_cancel_match_all(struct task_struct *task, > + bool (*match)(struct callback_head *, void *data), > + void *data) > +{ > + struct callback_head **pprev = &task->task_works; > + struct callback_head *work, *next; > + struct callback_head *head = NULL, **tail = &head; > + unsigned long flags; > + > + if (likely(!task_work_pending(task))) > + return NULL; > + > + raw_spin_lock_irqsave(&task->pi_lock, flags); > + work = READ_ONCE(*pprev); > + while (work && work != &work_exited) { > + next = READ_ONCE(work->next); > + if (!match(work, data)) { > + pprev = &work->next; > + work = next; > + continue; > + } > + > + if (!try_cmpxchg(pprev, &work, next)) > + continue; IIUC, you could ignore the cmpxchg here because the following loop iteration on the caller would catch it and retry. In this case, it no retry in io_wq_cancel_tw_create, which looks weird. Did I miss something? > + > + work->next = NULL; > + *tail = work; > + tail = &work->next; > + work = next; > + } > + raw_spin_unlock_irqrestore(&task->pi_lock, flags); > + > + return head; > +} > + > static bool task_work_func_match(struct callback_head *cb, void *data) > { > return cb->func == data; -- Gabriel Krisman Bertazi