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authorTakashi Iwai <tiwai@suse.de>2022-07-28 14:59:42 +0200
committerTakashi Iwai <tiwai@suse.de>2022-07-29 12:57:10 +0200
commitef34a0ae7a2654bc9e58675e36898217fb2799d8 (patch)
tree3444d3d9264ced511f8378bf656b276fe800cc97 /sound
parent87eb04bb87fbdf1d53f0fc64e6fc56ba2b504762 (diff)
ALSA: core: Add async signal helpers
Currently the call of kill_fasync() from an interrupt handler might lead to potential spin deadlocks, as spotted by syzkaller. Unfortunately, it's not so trivial to fix this lock chain as it's involved with the tasklist_lock that is touched in allover places. As a temporary workaround, this patch provides the way to defer the async signal notification in a work. The new helper functions, snd_fasync_helper() and snd_kill_faync() are replacements for fasync_helper() and kill_fasync(), respectively. In addition, snd_fasync_free() needs to be called at the destructor of the relevant file object. Link: https://lore.kernel.org/r/20220728125945.29533-2-tiwai@suse.de Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound')
-rw-r--r--sound/core/misc.c94
1 files changed, 94 insertions, 0 deletions
diff --git a/sound/core/misc.c b/sound/core/misc.c
index 50e4aaa6270d..d32a19976a2b 100644
--- a/sound/core/misc.c
+++ b/sound/core/misc.c
@@ -10,6 +10,7 @@
#include <linux/time.h>
#include <linux/slab.h>
#include <linux/ioport.h>
+#include <linux/fs.h>
#include <sound/core.h>
#ifdef CONFIG_SND_DEBUG
@@ -145,3 +146,96 @@ snd_pci_quirk_lookup(struct pci_dev *pci, const struct snd_pci_quirk *list)
}
EXPORT_SYMBOL(snd_pci_quirk_lookup);
#endif
+
+/*
+ * Deferred async signal helpers
+ *
+ * Below are a few helper functions to wrap the async signal handling
+ * in the deferred work. The main purpose is to avoid the messy deadlock
+ * around tasklist_lock and co at the kill_fasync() invocation.
+ * fasync_helper() and kill_fasync() are replaced with snd_fasync_helper()
+ * and snd_kill_fasync(), respectively. In addition, snd_fasync_free() has
+ * to be called at releasing the relevant file object.
+ */
+struct snd_fasync {
+ struct fasync_struct *fasync;
+ int signal;
+ int poll;
+ int on;
+ struct list_head list;
+};
+
+static DEFINE_SPINLOCK(snd_fasync_lock);
+static LIST_HEAD(snd_fasync_list);
+
+static void snd_fasync_work_fn(struct work_struct *work)
+{
+ struct snd_fasync *fasync;
+
+ spin_lock_irq(&snd_fasync_lock);
+ while (!list_empty(&snd_fasync_list)) {
+ fasync = list_first_entry(&snd_fasync_list, struct snd_fasync, list);
+ list_del_init(&fasync->list);
+ spin_unlock_irq(&snd_fasync_lock);
+ if (fasync->on)
+ kill_fasync(&fasync->fasync, fasync->signal, fasync->poll);
+ spin_lock_irq(&snd_fasync_lock);
+ }
+ spin_unlock_irq(&snd_fasync_lock);
+}
+
+static DECLARE_WORK(snd_fasync_work, snd_fasync_work_fn);
+
+int snd_fasync_helper(int fd, struct file *file, int on,
+ struct snd_fasync **fasyncp)
+{
+ struct snd_fasync *fasync = NULL;
+
+ if (on) {
+ fasync = kzalloc(sizeof(*fasync), GFP_KERNEL);
+ if (!fasync)
+ return -ENOMEM;
+ INIT_LIST_HEAD(&fasync->list);
+ }
+
+ spin_lock_irq(&snd_fasync_lock);
+ if (*fasyncp) {
+ kfree(fasync);
+ fasync = *fasyncp;
+ } else {
+ if (!fasync) {
+ spin_unlock_irq(&snd_fasync_lock);
+ return 0;
+ }
+ *fasyncp = fasync;
+ }
+ fasync->on = on;
+ spin_unlock_irq(&snd_fasync_lock);
+ 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)
+{
+ unsigned long flags;
+
+ if (!fasync || !fasync->on)
+ return;
+ spin_lock_irqsave(&snd_fasync_lock, flags);
+ fasync->signal = signal;
+ fasync->poll = poll;
+ list_move(&fasync->list, &snd_fasync_list);
+ schedule_work(&snd_fasync_work);
+ spin_unlock_irqrestore(&snd_fasync_lock, flags);
+}
+EXPORT_SYMBOL_GPL(snd_kill_fasync);
+
+void snd_fasync_free(struct snd_fasync *fasync)
+{
+ if (!fasync)
+ return;
+ fasync->on = 0;
+ flush_work(&snd_fasync_work);
+ kfree(fasync);
+}
+EXPORT_SYMBOL_GPL(snd_fasync_free);