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Sun, 25 Oct 2026 07:56:04 +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 1Fb/MRS23Wp+bwAAD6G6ig (envelope-from ); Sun, 25 Oct 2026 07:56:04 +0000 Date: Sun, 25 Oct 2026 08:56:04 +0100 Message-ID: <87o6ci6wob.wl-tiwai@suse.de> From: Takashi Iwai To: Cen Zhang Cc: perex@perex.cz, tiwai@suse.com, linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, jjzuming@gmail.com Subject: Re: [PATCH] ALSA: ump: Drain sequencer callbacks before freeing their client In-Reply-To: References: User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 Mule/6.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Spam-Flag: NO X-Spam-Level: X-Spamd-Result: default: False [-12.30 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_TLS_ALL(0.00)[]; TO_DN_SOME(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; FREEMAIL_TO(0.00)[gmail.com]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[perex.cz,suse.com,vger.kernel.org,gmail.com]; RCPT_COUNT_SEVEN(0.00)[7]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] X-Spam-Score: -12.30 On Sat, 24 Oct 2026 10:02:47 +0200, Cen Zhang wrote: > > seq_ump_client_free() cancels group_notify_work while the endpoint still > publishes seq_ops and seq_client. A received Function Block update can > enter the sequencer callback after cancellation and queue the work again. > Even disabling the work cannot protect a callback that already loaded > seq_client and then resumes after the client has been freed. > > A USB UMP endpoint can continue receiving while its sequencer binding > is removed. The following order uses the same endpoint and client: > > Sequencer binding removal UMP input completion > ------------------------- -------------------- > cancel_work_sync() > load seq_ops and seq_client > delete sequencer client > clear endpoint binding > kfree(client) > schedule group_notify_work > read client->seq_client > > Cover all calls through seq_ops with SRCU in the UMP core. Withdraw the > operations pointer and wait for those callbacks before canceling work > and deleting the client. No producer can then queue work after the final > cancellation, and both the client and callback code remain available > until the last in-flight callback returns. > > Publish seq_ops with release/acquire ordering so the separately stored > seq_client is initialized before any callback uses it. Use SRCU because > sequencer notification delivery can sleep; no callback needs to change > its existing execution context or allocation behavior. > > Fixes: 4a16a3af0571 ("ALSA: seq: ump: Handle FB info update") > Assisted-by: LLM > Signed-off-by: Cen Zhang Applied now. Thanks. Takashi