[PATCH v2 0/5] ALSA: Drop async signal support
Takashi Iwai
tiwai at suse.de
Mon Jul 25 16:52:31 CEST 2022
On Sun, 17 Jul 2022 12:16:13 +0200,
Jaroslav Kysela wrote:
>
> Dne 17. 07. 22 v 9:05 Takashi Iwai napsal(a):
> > Hi,
> >
> > this is a revised patch set for dropping fasync support from ALSA
> > core.
> >
> > The async signal itself is very difficult to use properly due to
> > various restrictions (e.g. you cannot perform any I/O in the context),
> > hence it's a feature that has been never used by real applications.
> >
> > OTOH, the real problem is that there have been quite a few syzcaller
> > reports indicating that fasync code path may lead to some potential
> > deadlocks for long time. Dropping the feature is the easiest
> > solution, obviously.
>
> I would probably prefer to fix the problem (deferred async kill or so). The
> SIGIO is just another way to wakeup the applications and there may be some
> corner cases, where this wakeup is usable (threaded apps). Note that we had
> some users (or testers) of SIGIO in past (at least there were questions about
> this support).
Hm, OK, then let's discard it for now.
The deferred kill_async() implementation would be something like below.
A quick test looks OK, so far, with the given syzkaller reproducer.
Ideally speaking, this should be fixed in the fasync sighandler side,
but it appears fragile -- kill_fasync() calls send_sigio(), and
send_sigio() takes read_lock(&tasklist_lock). And
read_lock(&tasklist_lock) itself is a common pattern taken in the
non/soft-IRQ contexts, which would conflict with the call in an
hard-IRQ context...
thanks,
Takashi
-- 8< --
diff --git a/include/sound/control.h b/include/sound/control.h
index fcd3cce673ec..eae443ba79ba 100644
--- a/include/sound/control.h
+++ b/include/sound/control.h
@@ -109,7 +109,7 @@ struct snd_ctl_file {
int preferred_subdevice[SND_CTL_SUBDEV_ITEMS];
wait_queue_head_t change_sleep;
spinlock_t read_lock;
- struct fasync_struct *fasync;
+ struct snd_fasync *fasync;
int subscribed; /* read interface is activated */
struct list_head events; /* waiting events for read */
};
diff --git a/include/sound/core.h b/include/sound/core.h
index dd28de2343b8..4365c35d038b 100644
--- a/include/sound/core.h
+++ b/include/sound/core.h
@@ -507,4 +507,12 @@ snd_pci_quirk_lookup_id(u16 vendor, u16 device,
}
#endif
+/* async signal helpers */
+struct snd_fasync;
+
+int snd_fasync_helper(int fd, struct file *file, int on,
+ struct snd_fasync **fasyncp);
+void snd_kill_fasync(struct snd_fasync *fasync, int signal, int poll);
+void snd_fasync_free(struct snd_fasync *fasync);
+
#endif /* __SOUND_CORE_H */
diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index 2d03c10f6a36..8c48a5bce88c 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -399,7 +399,7 @@ struct snd_pcm_runtime {
snd_pcm_uframes_t twake; /* do transfer (!poll) wakeup if non-zero */
wait_queue_head_t sleep; /* poll sleep */
wait_queue_head_t tsleep; /* transfer sleep */
- struct fasync_struct *fasync;
+ struct snd_fasync *fasync;
bool stop_operating; /* sync_stop will be called */
struct mutex buffer_mutex; /* protect for buffer changes */
atomic_t buffer_accessing; /* >0: in r/w operation, <0: blocked */
diff --git a/sound/core/control.c b/sound/core/control.c
index 4dba3a342458..f3e893715369 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -127,6 +127,7 @@ static int snd_ctl_release(struct inode *inode, struct file *file)
if (control->vd[idx].owner == ctl)
control->vd[idx].owner = NULL;
up_write(&card->controls_rwsem);
+ snd_fasync_free(ctl->fasync);
snd_ctl_empty_read_queue(ctl);
put_pid(ctl->pid);
kfree(ctl);
@@ -181,7 +182,7 @@ void snd_ctl_notify(struct snd_card *card, unsigned int mask,
_found:
wake_up(&ctl->change_sleep);
spin_unlock(&ctl->read_lock);
- kill_fasync(&ctl->fasync, SIGIO, POLL_IN);
+ snd_kill_fasync(ctl->fasync, SIGIO, POLL_IN);
}
read_unlock_irqrestore(&card->ctl_files_rwlock, flags);
}
@@ -2134,7 +2135,7 @@ static int snd_ctl_fasync(int fd, struct file * file, int on)
struct snd_ctl_file *ctl;
ctl = file->private_data;
- return fasync_helper(fd, file, on, &ctl->fasync);
+ return snd_fasync_helper(fd, file, on, &ctl->fasync);
}
/* return the preferred subdevice number if already assigned;
@@ -2302,7 +2303,7 @@ static int snd_ctl_dev_disconnect(struct snd_device *device)
read_lock_irqsave(&card->ctl_files_rwlock, flags);
list_for_each_entry(ctl, &card->ctl_files, list) {
wake_up(&ctl->change_sleep);
- kill_fasync(&ctl->fasync, SIGIO, POLL_ERR);
+ snd_kill_fasync(ctl->fasync, SIGIO, POLL_ERR);
}
read_unlock_irqrestore(&card->ctl_files_rwlock, flags);
diff --git a/sound/core/misc.c b/sound/core/misc.c
index 50e4aaa6270d..f9d100905b98 100644
--- a/sound/core/misc.c
+++ b/sound/core/misc.c
@@ -145,3 +145,53 @@ snd_pci_quirk_lookup(struct pci_dev *pci, const struct snd_pci_quirk *list)
}
EXPORT_SYMBOL(snd_pci_quirk_lookup);
#endif
+
+/* async signal helpers */
+struct snd_fasync {
+ struct fasync_struct *fasync;
+ struct work_struct work;
+ int signal;
+ int poll;
+};
+
+static void snd_fasync_work(struct work_struct *work)
+{
+ struct snd_fasync *fasync = container_of(work, struct snd_fasync, work);
+
+ kill_fasync(&fasync->fasync, fasync->signal, fasync->poll);
+}
+
+int snd_fasync_helper(int fd, struct file *file, int on,
+ struct snd_fasync **fasyncp)
+{
+ struct snd_fasync *fasync = *fasyncp;
+
+ if (!fasync) {
+ fasync = kzalloc(sizeof(*fasync), GFP_KERNEL);
+ if (!fasync)
+ return -ENOMEM;
+ INIT_WORK(&fasync->work, snd_fasync_work);
+ *fasyncp = fasync;
+ }
+ return fasync_helper(fd, file, on, &fasync->fasync);
+}
+EXPORT_SYMBOL_GPL(snd_fasync_helper);
+
+void snd_kill_fasync(struct snd_fasync *fasync, int signal, int poll)
+{
+ if (!fasync)
+ return;
+ fasync->signal = signal;
+ fasync->poll = poll;
+ schedule_work(&fasync->work);
+}
+EXPORT_SYMBOL_GPL(snd_kill_fasync);
+
+void snd_fasync_free(struct snd_fasync *fasync)
+{
+ if (!fasync)
+ return;
+ cancel_work_sync(&fasync->work);
+ kfree(fasync);
+}
+EXPORT_SYMBOL_GPL(snd_fasync_free);
diff --git a/sound/core/pcm.c b/sound/core/pcm.c
index 03fc5fa5813e..2ac742035310 100644
--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -1007,6 +1007,7 @@ void snd_pcm_detach_substream(struct snd_pcm_substream *substream)
substream->runtime = NULL;
}
mutex_destroy(&runtime->buffer_mutex);
+ snd_fasync_free(runtime->fasync);
kfree(runtime);
put_pid(substream->pid);
substream->pid = NULL;
diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index 1fc7c50ffa62..40751e5aff09 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1822,7 +1822,7 @@ void snd_pcm_period_elapsed_under_stream_lock(struct snd_pcm_substream *substrea
snd_timer_interrupt(substream->timer, 1);
#endif
_end:
- kill_fasync(&runtime->fasync, SIGIO, POLL_IN);
+ snd_kill_fasync(runtime->fasync, SIGIO, POLL_IN);
}
EXPORT_SYMBOL(snd_pcm_period_elapsed_under_stream_lock);
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index aa0453e51595..ad0541e9e888 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -3951,7 +3951,7 @@ static int snd_pcm_fasync(int fd, struct file * file, int on)
runtime = substream->runtime;
if (runtime->status->state == SNDRV_PCM_STATE_DISCONNECTED)
return -EBADFD;
- return fasync_helper(fd, file, on, &runtime->fasync);
+ return snd_fasync_helper(fd, file, on, &runtime->fasync);
}
/*
diff --git a/sound/core/timer.c b/sound/core/timer.c
index b3214baa8919..e08a37c23add 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -83,7 +83,7 @@ struct snd_timer_user {
unsigned int filter;
struct timespec64 tstamp; /* trigger tstamp */
wait_queue_head_t qchange_sleep;
- struct fasync_struct *fasync;
+ struct snd_fasync *fasync;
struct mutex ioctl_lock;
};
@@ -1345,7 +1345,7 @@ static void snd_timer_user_interrupt(struct snd_timer_instance *timeri,
}
__wake:
spin_unlock(&tu->qlock);
- kill_fasync(&tu->fasync, SIGIO, POLL_IN);
+ snd_kill_fasync(tu->fasync, SIGIO, POLL_IN);
wake_up(&tu->qchange_sleep);
}
@@ -1383,7 +1383,7 @@ static void snd_timer_user_ccallback(struct snd_timer_instance *timeri,
spin_lock_irqsave(&tu->qlock, flags);
snd_timer_user_append_to_tqueue(tu, &r1);
spin_unlock_irqrestore(&tu->qlock, flags);
- kill_fasync(&tu->fasync, SIGIO, POLL_IN);
+ snd_kill_fasync(tu->fasync, SIGIO, POLL_IN);
wake_up(&tu->qchange_sleep);
}
@@ -1453,7 +1453,7 @@ static void snd_timer_user_tinterrupt(struct snd_timer_instance *timeri,
spin_unlock(&tu->qlock);
if (append == 0)
return;
- kill_fasync(&tu->fasync, SIGIO, POLL_IN);
+ snd_kill_fasync(tu->fasync, SIGIO, POLL_IN);
wake_up(&tu->qchange_sleep);
}
@@ -1521,6 +1521,7 @@ static int snd_timer_user_release(struct inode *inode, struct file *file)
snd_timer_instance_free(tu->timeri);
}
mutex_unlock(&tu->ioctl_lock);
+ snd_fasync_free(tu->fasync);
kfree(tu->queue);
kfree(tu->tqueue);
kfree(tu);
@@ -2135,7 +2136,7 @@ static int snd_timer_user_fasync(int fd, struct file * file, int on)
struct snd_timer_user *tu;
tu = file->private_data;
- return fasync_helper(fd, file, on, &tu->fasync);
+ return snd_fasync_helper(fd, file, on, &tu->fasync);
}
static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
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