Re: [alsa-devel] sound: list corruption in delete_and_unsubscribe_port

On Tue, Feb 16, 2016 at 11:00 AM, Takashi Iwai tiwai@suse.de wrote:

On Tue, 16 Feb 2016 10:41:54 +0100, Dmitry Vyukov wrote:

...

Hello,

Here is a new one on 18558cae0272f8fd9647e69d3fec1565a7949865 (4.5-rc4). But need to note that sound become much more stable, I've seen only 2 of these over night.

The following program causes list corruption:

------------[ cut here ]------------ WARNING: CPU: 2 PID: 12546 at lib/list_debug.c:62 __list_del_entry+0x10b/0x1e0() list_del corruption, ffff880063512388->next is LIST_POISON1 (dead000000000100) Modules linked in: CPU: 2 PID: 12546 Comm: a.out Not tainted 4.5.0-rc4+ #328 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 ffffffff87b05080 ffff8800608b7a48 ffffffff82be46cf ffffffff81477fb8 fffffbfff0f60a10 ffff8800608b7ab8 ffff8800637d97c0 ffffffff86ad3780 0000000000000009 000000000000003e ffff8800608b7a88 ffffffff81355139 Call Trace: [<ffffffff81355249>] warn_slowpath_fmt+0xa9/0xd0 kernel/panic.c:494 [<ffffffff82c4c36b>] __list_del_entry+0x10b/0x1e0 lib/list_debug.c:60 [<ffffffff82c4c44d>] list_del+0xd/0x70 lib/list_debug.c:86 [<ffffffff852c38e3>] delete_and_unsubscribe_port+0x1e3/0x2f0 sound/core/seq/seq_ports.c:545 [<ffffffff852c43fa>] clear_subscriber_list+0x15a/0x260 sound/core/seq/seq_ports.c:250 [<ffffffff852c456a>] port_delete+0x6a/0x1c0 sound/core/seq/seq_ports.c:266 [<ffffffff852c5242>] snd_seq_delete_all_ports+0x242/0x350 sound/core/seq/seq_ports.c:330 [<ffffffff852ae1cf>] seq_free_client1+0x2f/0x290 sound/core/seq/seq_clientmgr.c:272 [<ffffffff852ae495>] seq_free_client+0x65/0x160 sound/core/seq/seq_clientmgr.c:299 [<ffffffff852b118d>] snd_seq_release+0x4d/0xb0 sound/core/seq/seq_clientmgr.c:380 [<ffffffff817c3256>] __fput+0x236/0x780 fs/file_table.c:208 [<ffffffff817c3825>] ____fput+0x15/0x20 fs/file_table.c:244 [<ffffffff813b3100>] task_work_run+0x170/0x210 kernel/task_work.c:115 [< inline >] tracehook_notify_resume include/linux/tracehook.h:191 [<ffffffff810066b1>] exit_to_usermode_loop+0x1d1/0x210 arch/x86/entry/common.c:251 [< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:282 [<ffffffff810084ea>] syscall_return_slowpath+0x2ba/0x340 arch/x86/entry/common.c:344 [<ffffffff866626e2>] int_ret_from_sys_call+0x25/0x9f arch/x86/entry/entry_64.S:281 ---[ end trace 4cad985f706f8ace ]---

Hm, this might be the remaining open race at deleting ports. Please try the patch below.

Yes, it fixes the crash for me.

Tested-by: Dmitry Vyukov dvyukov@google.com

Thanks!

thanks,

Takashi

---

diff --git a/sound/core/seq/seq_ports.c b/sound/core/seq/seq_ports.c index 921fb2bd8fad..fe686ee41c6d 100644 --- a/sound/core/seq/seq_ports.c +++ b/sound/core/seq/seq_ports.c @@ -535,19 +535,22 @@ static void delete_and_unsubscribe_port(struct snd_seq_client *client, bool is_src, bool ack) { struct snd_seq_port_subs_info *grp;

•   struct list_head *list;
  

•   bool empty;
  
    grp = is_src ? &port->c_src : &port->c_dest;
  

•   list = is_src ? &subs->src_list : &subs->dest_list;
    down_write(&grp->list_mutex);
    write_lock_irq(&grp->list_lock);
  

•   if (is_src)
  

•           list_del(&subs->src_list);
  

•   else
  

•           list_del(&subs->dest_list);
  

•   empty = list_empty(list);
  

•   if (!empty)
  

•           list_del_init(list);
    grp->exclusive = 0;
    write_unlock_irq(&grp->list_lock);
    up_write(&grp->list_mutex);
  
  

•   unsubscribe_port(client, port, grp, &subs->info, ack);
  

•   if (!empty)
  

•           unsubscribe_port(client, port, grp, &subs->info, ack);
  

}

/* connect two ports */