Hello Takashi, Thank you very much for your feedback! > -----Original Message----- > From: Takashi Iwai [mailto:tiwai@xxxxxxx] > Sent: Thursday, November 07, 2019 11:06 AM > To: Gabbasov, Andrew > Cc: alsa-devel@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Jaroslav > Kysela; Takashi Iwai; Timo Wischer > Subject: Re: [PATCH v2 8/8] ALSA: aloop: Support runtime change of > snd_timer via info interface > > On Tue, 05 Nov 2019 15:32:18 +0100, > Andrew Gabbasov wrote: > > > > Show and change sound card timer source with read-write info > > file in proc filesystem. Initial string can still be set as > > module parameter. > > > > The timer source string value can be changed at any time, > > but it is latched by PCM substream open callback (the first one > > for a particular cable). At this point it is actually used, that > > is the string is parsed, and the timer is looked up and opened. > > > > The timer source is set for a loopback card (the same as initial > > setting by module parameter), but every cable uses the value, > > current at the moment of open. > > > > Setting the value to empty string switches the timer to jiffies. > > > > Signed-off-by: Andrew Gabbasov <andrew_gabbasov@xxxxxxxxxx> > > Unfortunately the whole code here are racy. It may lead to a crash or > use-after-free easily. Some locking is needed definitely. You are right, using and changing of loopback->timer_source should be protected. I'll add locking with loopback->cable_lock to the bodies of print_timer_source_info() and change_timer_source_info() (like in the example diff below), similarly to other /proc files and mixer controls. All other uses of loopback->timer_source are already covered by loopback->cable_lock, except for loopback_set_timer_source() call from loopback_probe(), that is done at the very early stage and doesn't conflict with other uses. I think, in order to avoid racing problems, this will be enough, won't it? Thanks. Best regards, Andrew diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c index 415128a97774..ca9307dd780e 100644 --- a/sound/drivers/aloop.c +++ b/sound/drivers/aloop.c @@ -1684,8 +1684,10 @@ static void print_timer_source_info(struct snd_info_entry *entry, { struct loopback *loopback = entry->private_data; + mutex_lock(&loopback->cable_lock); snd_iprintf(buffer, "%s\n", loopback->timer_source ? loopback->timer_source : ""); + mutex_unlock(&loopback->cable_lock); } static void change_timer_source_info(struct snd_info_entry *entry, @@ -1694,8 +1696,10 @@ static void change_timer_source_info(struct snd_info_entry *entry, struct loopback *loopback = entry->private_data; char line[64]; + mutex_lock(&loopback->cable_lock); if (!snd_info_get_line(buffer, line, sizeof(line))) loopback_set_timer_source(loopback, strim(line)); + mutex_unlock(&loopback->cable_lock); } static int loopback_timer_source_proc_new(struct loopback *loopback) _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
