From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.223.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 71690205E00 for ; Fri, 18 Apr 2025 11:08:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=195.135.223.131 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744974517; cv=none; b=t0cnXaW12ZP4mqpc+Cti+4sHo8Z54BWTyielrJ8gJhNJVeOkek4vZsijvt2cIZARbCYrmVUneRVJfrxAzE9AYrvGo1JMXtubNxAP5GSGyHW7fOmSz/PCP7dQeX8IiHP59xA6KhKjY9XzjvKxEibq64C8eMWeKxfRICBMk8dMY3E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744974517; c=relaxed/simple; bh=15ntGwiZUJaVMPPEUSrPQSIGAsEyqn03pKC/jI1niXA=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=AIrapZ8pUXi6acCfqqnAwBk/+cF8O/4rc7dwjhak+kF0ZU9SAALFEDzRmX5GY4pk6y644r+Ven6is8qdBL0LLjsYzG8meKigcult57ndIAhJ9ksxuWZYtPyHLz6tPkCAgRhGHyS0zCAMC1GW1V51VdmRRlqeISkV4RZatWUCGJg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=suse.de; spf=pass smtp.mailfrom=suse.de; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b=uWuFlcDy; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b=rQTOOSqj; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b=uWuFlcDy; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b=rQTOOSqj; arc=none smtp.client-ip=195.135.223.131 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=suse.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b="uWuFlcDy"; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b="rQTOOSqj"; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b="uWuFlcDy"; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b="rQTOOSqj" Received: from imap1.dmz-prg2.suse.org (unknown [10.150.64.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 518D21F770; Fri, 18 Apr 2025 11:08:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1744974513; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8Tn8D02kaMX0c/5P7w+cgqBjbKeXlSQDQopNVCUQYV4=; b=uWuFlcDydppCRW+UbXlB2H6YVWXeZvS7wiegzYGPIF3MBMS45mascd+3mDBdrmTAcSsOKS viQAkzIrPyBf3Ev1L7lkQ5/kJNe8nJpWv7wLAwGChwCq+/4r5+5ZlQXZW8p9QTwx9vwDid YvngROeNgY9RmcSirSz+uotid8DW18E= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1744974513; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8Tn8D02kaMX0c/5P7w+cgqBjbKeXlSQDQopNVCUQYV4=; b=rQTOOSqjBl/T8hjuZ5vlTPVJbTvW82z28KrJd7C3G+bD0RfRrpxjzHQUFxCaTXFlqgUjlF qd3EtcC2QUZ1mFBw== Authentication-Results: smtp-out2.suse.de; none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1744974513; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8Tn8D02kaMX0c/5P7w+cgqBjbKeXlSQDQopNVCUQYV4=; b=uWuFlcDydppCRW+UbXlB2H6YVWXeZvS7wiegzYGPIF3MBMS45mascd+3mDBdrmTAcSsOKS viQAkzIrPyBf3Ev1L7lkQ5/kJNe8nJpWv7wLAwGChwCq+/4r5+5ZlQXZW8p9QTwx9vwDid YvngROeNgY9RmcSirSz+uotid8DW18E= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1744974513; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8Tn8D02kaMX0c/5P7w+cgqBjbKeXlSQDQopNVCUQYV4=; b=rQTOOSqjBl/T8hjuZ5vlTPVJbTvW82z28KrJd7C3G+bD0RfRrpxjzHQUFxCaTXFlqgUjlF qd3EtcC2QUZ1mFBw== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 22C5313942; Fri, 18 Apr 2025 11:08:33 +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 pjPtBrEyAmiXNQAAD6G6ig (envelope-from ); Fri, 18 Apr 2025 11:08:33 +0000 Date: Fri, 18 Apr 2025 13:08:32 +0200 Message-ID: <87a58dvia7.wl-tiwai@suse.de> From: Takashi Iwai To: Hillf Danton Cc: alsa-devel@alsa-project.org, Mikhail Gavrilov , LKML Subject: Re: [PATCH 2/9] ALSA: usb-audio: Fix possible race at sync of urb completions In-Reply-To: <20250418103533.4078-1-hdanton@sina.com> References: <20210929080844.11583-1-tiwai@suse.de> <20210929080844.11583-3-tiwai@suse.de> <20250418103533.4078-1-hdanton@sina.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Spam-Level: X-Spamd-Result: default: False [-1.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; 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]; TAGGED_RCPT(0.00)[]; RCVD_TLS_ALL(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; FREEMAIL_TO(0.00)[sina.com]; FREEMAIL_ENVRCPT(0.00)[gmail.com,sina.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[alsa-project.org,gmail.com,vger.kernel.org]; RCPT_COUNT_THREE(0.00)[4]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.de:mid] X-Spam-Score: -1.80 X-Spam-Flag: NO On Fri, 18 Apr 2025 12:35:32 +0200, Hillf Danton wrote: > > On Wed, 29 Sep 2021 10:08:37 +0200 Takashi Iwai wrote: > > USB-audio driver tries to sync with the clear of all pending URBs in > > wait_clear_urbs(), and it waits for all bits in active_mask getting > > cleared. This works fine for the normal operations, but when a stream > > is managed in the implicit feedback mode, there is still a very thin > > race window: namely, in snd_complete_usb(), the active_mask bit for > > the current URB is once cleared before re-submitted in > > queue_pending_output_urbs(). If wait_clear_urbs() is called during > > that period, it may pass the test and go forward even though there may > > be a still pending URB. > > > > For covering it, this patch adds a new counter to each endpoint to > > keep the number of in-flight URBs, and changes wait_clear_urbs() > > checking this number instead. The counter is decremented at the end > > of URB complete, hence the reference is kept as long as the URB > > complete is in process. > > > > Signed-off-by: Takashi Iwai > > --- > > sound/usb/card.h | 1 + > > sound/usb/endpoint.c | 7 ++++++- > > 2 files changed, 7 insertions(+), 1 deletion(-) > > > > diff --git a/sound/usb/card.h b/sound/usb/card.h > > index 3329ce710cb9..746a765b2437 100644 > > --- a/sound/usb/card.h > > +++ b/sound/usb/card.h > > @@ -97,6 +97,7 @@ struct snd_usb_endpoint { > > unsigned int nominal_queue_size; /* total buffer sizes in URBs */ > > unsigned long active_mask; /* bitmask of active urbs */ > > unsigned long unlink_mask; /* bitmask of unlinked urbs */ > > + atomic_t submitted_urbs; /* currently submitted urbs */ > > char *syncbuf; /* sync buffer for all sync URBs */ > > dma_addr_t sync_dma; /* DMA address of syncbuf */ > > > > diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c > > index 29c4865966f5..06241568abf7 100644 > > --- a/sound/usb/endpoint.c > > +++ b/sound/usb/endpoint.c > > @@ -451,6 +451,7 @@ static void queue_pending_output_urbs(struct snd_usb_endpoint *ep) > > } > > > > set_bit(ctx->index, &ep->active_mask); > > + atomic_inc(&ep->submitted_urbs); > > } > > } > > > > @@ -488,6 +489,7 @@ static void snd_complete_urb(struct urb *urb) > > clear_bit(ctx->index, &ep->active_mask); > > spin_unlock_irqrestore(&ep->lock, flags); > > queue_pending_output_urbs(ep); > > smp_mb(); > > > + atomic_dec(&ep->submitted_urbs); /* decrement at last */ > > Does it match the comment to add a mb? How...? I don't understand your intention. Takashi