[alsa-devel] sound: another deadlock in snd_seq_pool_done

[Takashi Iwai]

On Sat, 04 Mar 2017 17:31:21 +0100,
Dmitry Vyukov wrote:
> 
> Hello,
> 
> The following program creates processes deadlocked in snd_seq_pool_done:
> 
> https://gist.githubusercontent.com/dvyukov/97efc9cb6d63b1b2c7b737b82cc8b0d6/raw/3546b133ae0b2d3e1190ae7c1f4e240ce7ce132e/gistfile1.txt
> 
> After few seconds I get:
> 
> # ps afxu | grep a.out
> root      8660  2.0  0.0      0     0 pts/0    Zl   16:27   0:00
> [a.out] <defunct>
> 
> # kill -9 8660
> 
> # cat /proc/8660/status
> Name: a.out
> State: Z (zombie)
> Tgid: 8660
> Ngid: 0
> Pid: 8660
> PPid: 1
> TracerPid: 0
> Uid: 0 0 0 0
> Gid: 0 0 0 0
> FDSize: 0
> Groups: 0
> NStgid: 8660
> NSpid: 8660
> NSpgid: 8660
> NSsid: 2971
> Threads: 2
> SigQ: 1/3304
> SigPnd: 0000000000000000
> ShdPnd: 0000000000000100
> SigBlk: 0000000000000000
> SigIgn: 0000000180000000
> SigCgt: 0000000000000440
> CapInh: 0000000000000000
> CapPrm: 0000003fffffffff
> CapEff: 0000003fffffffff
> CapBnd: 0000003fffffffff
> CapAmb: 0000000000000000
> NoNewPrivs: 0
> Seccomp: 0
> Cpus_allowed: f
> Cpus_allowed_list: 0-3
> Mems_allowed: 00000000,00000001
> Mems_allowed_list: 0
> voluntary_ctxt_switches: 12
> nonvoluntary_ctxt_switches: 0
> 
> # cat /proc/8660/task/*/stack
> [<ffffffff835406db>] snd_seq_pool_done+0x31b/0x620
> sound/core/seq/seq_memory.c:436
> [<ffffffff8353a11e>] snd_seq_ioctl_set_client_pool+0x1ae/0x600
> sound/core/seq/seq_clientmgr.c:1836
> [<ffffffff835382ba>] snd_seq_ioctl+0x2da/0x4d0
> sound/core/seq/seq_clientmgr.c:2130
> [<ffffffff81aced2f>] vfs_ioctl fs/ioctl.c:45 [inline]
> [<ffffffff81aced2f>] do_vfs_ioctl+0x1bf/0x1790 fs/ioctl.c:685
> [<ffffffff81ad038f>] SYSC_ioctl fs/ioctl.c:700 [inline]
> [<ffffffff81ad038f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
> [<ffffffff8457dc41>] entry_SYSCALL_64_fastpath+0x1f/0xc2

Now I've been trying to reproduce the hang, alas it didn't happen on
my VM by some reason.

In anyway, below is an untested fix for possible races against
snd_seq_pool_done() and cell insertions.  Could you check whether it
cures your issue?


thanks,

Takashi

---
diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
index 4c935202ce23..f3b1d7f50b81 100644
--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -1832,6 +1832,7 @@ static int snd_seq_ioctl_set_client_pool(struct snd_seq_client *client,
 	     info->output_pool != client->pool->size)) {
 		if (snd_seq_write_pool_allocated(client)) {
 			/* remove all existing cells */
+			snd_seq_pool_mark_closing(client->pool);
 			snd_seq_queue_client_leave_cells(client->number);
 			snd_seq_pool_done(client->pool);
 		}
diff --git a/sound/core/seq/seq_fifo.c b/sound/core/seq/seq_fifo.c
index 448efd4e980e..33980d1c8037 100644
--- a/sound/core/seq/seq_fifo.c
+++ b/sound/core/seq/seq_fifo.c
@@ -72,6 +72,9 @@ void snd_seq_fifo_delete(struct snd_seq_fifo **fifo)
 		return;
 	*fifo = NULL;
 
+	if (f->pool)
+		snd_seq_pool_mark_closing(f->pool);
+
 	snd_seq_fifo_clear(f);
 
 	/* wake up clients if any */
diff --git a/sound/core/seq/seq_memory.c b/sound/core/seq/seq_memory.c
index 1a1acf3ddda4..d4c61ec9be13 100644
--- a/sound/core/seq/seq_memory.c
+++ b/sound/core/seq/seq_memory.c
@@ -415,6 +415,18 @@ int snd_seq_pool_init(struct snd_seq_pool *pool)
 	return 0;
 }
 
+/* refuse the further insertion to the pool */
+void snd_seq_pool_mark_closing(struct snd_seq_pool *pool)
+{
+	unsigned long flags;
+
+	if (snd_BUG_ON(!pool))
+		return;
+	spin_lock_irqsave(&pool->lock, flags);
+	pool->closing = 1;
+	spin_unlock_irqrestore(&pool->lock, flags);
+}
+
 /* remove events */
 int snd_seq_pool_done(struct snd_seq_pool *pool)
 {
@@ -425,10 +437,6 @@ int snd_seq_pool_done(struct snd_seq_pool *pool)
 		return -EINVAL;
 
 	/* wait for closing all threads */
-	spin_lock_irqsave(&pool->lock, flags);
-	pool->closing = 1;
-	spin_unlock_irqrestore(&pool->lock, flags);
-
 	if (waitqueue_active(&pool->output_sleep))
 		wake_up(&pool->output_sleep);
 
@@ -485,6 +493,7 @@ int snd_seq_pool_delete(struct snd_seq_pool **ppool)
 	*ppool = NULL;
 	if (pool == NULL)
 		return 0;
+	snd_seq_pool_mark_closing(pool);
 	snd_seq_pool_done(pool);
 	kfree(pool);
 	return 0;
diff --git a/sound/core/seq/seq_memory.h b/sound/core/seq/seq_memory.h
index 4a2ec779b8a7..32f959c17786 100644
--- a/sound/core/seq/seq_memory.h
+++ b/sound/core/seq/seq_memory.h
@@ -84,6 +84,7 @@ static inline int snd_seq_total_cells(struct snd_seq_pool *pool)
 int snd_seq_pool_init(struct snd_seq_pool *pool);
 
 /* done pool - free events */
+void snd_seq_pool_mark_closing(struct snd_seq_pool *pool);
 int snd_seq_pool_done(struct snd_seq_pool *pool);
 
 /* create pool */