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Tue, 11 Aug 2026 17:02:08 +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 X4LrMZBVe2rdOQAAD6G6ig (envelope-from ); Tue, 11 Aug 2026 17:02:08 +0000 From: Gabriel Krisman Bertazi To: Vishnu Razdan via B4 Relay , axboe@kernel.dk Cc: io-uring@vger.kernel.org, vrazdan@openai.com, linux-kernel@vger.kernel.org, asml.silence@gmail.com Subject: Re: [PATCH] io_uring/io-wq: fix worker accounting when canceling creation callbacks In-Reply-To: <20260811-vrazdan-io-wq-b4-submit-v1-1-719ced16c921@openai.com> Organization: SUSE References: <20260811-vrazdan-io-wq-b4-submit-v1-1-719ced16c921@openai.com> Date: Tue, 11 Aug 2026 13:02:07 -0400 Message-ID: <87mruspp4g.fsf@mailhost.krisman.be> 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-Score: -3.01 X-Spam-Level: X-Rspamd-Action: no action X-Rspamd-Queue-Id: 59AE281DEE X-Spamd-Result: default: False [-3.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; 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)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; HAS_ORG_HEADER(0.00)[]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; RCVD_TLS_ALL(0.00)[]; RCPT_COUNT_FIVE(0.00)[6]; RCVD_COUNT_TWO(0.00)[2]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[vger.kernel.org,openai.com,gmail.com]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; RCVD_VIA_SMTP_AUTH(0.00)[]; TAGGED_RCPT(0.00)[vrazdan.openai.com]; DKIM_TRACE(0.00)[suse.de:+]; MISSING_XM_UA(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns,mailhost.krisman.be:mid,openai.com:email,suse.de:email,suse.de:dkim] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spam-Flag: NO Vishnu Razdan via B4 Relay writes: > From: Vishnu Razdan > > create_worker_cb() reserves an io-wq worker slot only after its > task-work callback runs. If the callback is canceled before then, > io_worker_cancel_cb() still decrements acct->nr_workers. When an > existing worker retires with its creation callback pending, that > worker has already decremented the same account's worker count. > > The resulting undercount permits worker creation beyond the account's > configured limit. On an AST2600 OpenBMC system, an unchanged sensor > daemon reached 4,291 threads with the original kernel. With an > equivalent downstream fix, 25 passive samples under its normal > workload showed 6-9 threads. > > Decrement nr_workers only when the canceled callback is not > create_worker_cb(). Continuation callbacks still release their reserved > slot, and both callback types retain the existing running-count, > reference-count, and create-state cleanup. > > Fixes: 1d5f5ea7cb7d ("io-wq: remove worker to owner tw dependency") > Cc: stable@vger.kernel.org > Assisted-by: Codex:gpt-5.6-sol > Signed-off-by: Vishnu Razdan > --- Reviewed-by: Gabriel Krisman Bertazi > Prevent unreserved worker-creation callbacks from decrementing the worker count. > --- > io_uring/io-wq.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c > index 2e14880ee..fa403ed24 100644 > --- a/io_uring/io-wq.c > +++ b/io_uring/io-wq.c > @@ -211,9 +211,12 @@ static void io_worker_cancel_cb(struct io_worker *worker) > struct io_wq *wq = worker->wq; > > atomic_dec(&acct->nr_running); > - raw_spin_lock(&acct->workers_lock); > - acct->nr_workers--; > - raw_spin_unlock(&acct->workers_lock); > + /* create_worker_cb() has not reserved a worker slot yet. */ > + if (worker->create_work.func != create_worker_cb) { > + raw_spin_lock(&acct->workers_lock); > + acct->nr_workers--; > + raw_spin_unlock(&acct->workers_lock); > + } > io_worker_ref_put(wq); > clear_bit_unlock(0, &worker->create_state); > io_worker_release(worker); > > --- > base-commit: d58772d8520c7ef247c4b95c9bd76d3a25da9ff5 > change-id: 20260810-vrazdan-io-wq-b4-submit-9c94df145718 > > Best regards, > -- > Vishnu Razdan > > -- Gabriel Krisman Bertazi