[alsa-devel] sound: WARNING in snd_rawmidi_transmit_ack

[Takashi Iwai]

On Sun, 24 Jan 2016 17:29:12 +0100,
Dmitry Vyukov wrote:
> 
> Hello,
> 
> The following program triggers WARNING in snd_rawmidi_transmit_ack:
> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 20739 at sound/core/rawmidi.c:1136
> snd_rawmidi_transmit_ack+0x275/0x400()
> Modules linked in:
> CPU: 1 PID: 20739 Comm: syz-executor Tainted: G        W       4.4.0+ #276
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>  00000000ffffffff ffff8800346af8d8 ffffffff82999e2d 0000000000000000
>  ffff88002fea97c0 ffffffff86d3f920 ffff8800346af918 ffffffff81352089
>  ffffffff84f80bd5 ffffffff86d3f920 0000000000000470 ffff8800600b9b68
> Call Trace:
>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>  [<ffffffff82999e2d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
>  [<ffffffff81352089>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482
>  [<ffffffff813522b9>] warn_slowpath_null+0x29/0x30 kernel/panic.c:515
>  [<ffffffff84f80bd5>] snd_rawmidi_transmit_ack+0x275/0x400
> sound/core/rawmidi.c:1136
>  [<ffffffff84fdb3c1>] snd_virmidi_output_trigger+0x4b1/0x5a0
> sound/core/seq/seq_virmidi.c:163
>  [<     inline     >] snd_rawmidi_output_trigger sound/core/rawmidi.c:150
>  [<ffffffff84f87ed9>] snd_rawmidi_kernel_write1+0x549/0x780
> sound/core/rawmidi.c:1223
>  [<ffffffff84f89fd3>] snd_rawmidi_write+0x543/0xb30 sound/core/rawmidi.c:1273
>  [<ffffffff817b0323>] __vfs_write+0x113/0x480 fs/read_write.c:528
>  [<ffffffff817b1db7>] vfs_write+0x167/0x4a0 fs/read_write.c:577
>  [<     inline     >] SYSC_write fs/read_write.c:624
>  [<ffffffff817b50a1>] SyS_write+0x111/0x220 fs/read_write.c:616
>  [<ffffffff86336c36>] entry_SYSCALL_64_fastpath+0x16/0x7a
> arch/x86/entry/entry_64.S:185
> ---[ end trace 93509ba74cc3e259 ]---
> 
> 
> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> #include <pthread.h>
> #include <stdint.h>
> #include <string.h>
> #include <sys/syscall.h>
> #include <unistd.h>
> #include <fcntl.h>
> 
> long r[11];
> 
> void* thr(void* arg)
> {
>   switch ((long)arg) {
>   case 0:
>     r[0] = syscall(SYS_mmap, 0x20000000ul, 0x10000ul, 0x3ul, 0x32ul,
>                    0xfffffffffffffffful, 0x0ul);
>     break;
>   case 1:
>     r[1] = syscall(SYS_open, "/dev/dmmidi2", O_RDWR, 0);
>     break;
>   case 2:
>     *(uint32_t*)0x20006fda = (uint32_t)0x28;
>     *(uint32_t*)0x20006fde = (uint32_t)0x7;
>     *(uint64_t*)0x20006fe2 = (uint64_t)0x0;
>     *(uint64_t*)0x20006fea = (uint64_t)0x7;
>     *(uint64_t*)0x20006ff2 = (uint64_t)0x8;
>     *(uint16_t*)0x20006ffa = (uint16_t)0xfffffffffffffff8;
>     r[8] = syscall(SYS_write, r[1], 0x20006fdaul, 0x28ul, 0, 0, 0);
>     break;
>   case 3:
>     memcpy((void*)0x20007000,
>            "\x3c\x3f\xbc\xd7\x07\xee\x01\x21\x84\x26\x11\x6d\xc6\xc3"
>            "\xac\x7f\x14\xa3\x15\xda\xa1\x34\x67\xe9\xb6\xf8\xa8\xdd"
>            "\xb5\xe0\x2a\x64\x6e\x04\x7c\x40\xdb\x64\x4f\x53\x41\x90"
>            "\x02\x3b\x48\xba\xf6\xd7\x32\xe5\x11\x3f\xe5\xc5\xf2\x5f"
>            "\x4e\x6f\x5b\xe9\x0e\x76\x1a\x72\x77\x68\xad\xd3\x1b\x8d"
>            "\x8f\x71\x2f\x40\xde\xf4\xbf\x78\x48\xc2\xc3\xe5\xe9\x11"
>            "\x11\xd2\x9a\x91\x94\x81\x57\x22\xef\x2a\x5b\xe2\x9e\xce"
>            "\x3f\xa6\x07\x54\xd4\xb6\x1f\x30\xfd\x09\x35\x54\xcc\x78"
>            "\x12\x37\x59\xf7\x5c\x51\xd2\x47\xb8\x40\x98\x2b\xb4\x8d"
>            "\xbf\xd5\x34\x26\xcd\xb5\xe4\x98\x2d\x0e\xb1\x71\x0f\x12"
>            "\x06\xb0\x2c\x78\x74\xba\x3d\x32\x9c\x72\x96\x0d\x91\x50"
>            "\x9a\xe3\xbc\x4f\x1e\x26\xb2\xe3\xb2\xa2\x68\x6f\x10\xb5"
>            "\xc1\x7f\xfc\xfd\xf0\xe6\xd9\x0c\xa0\xa7\x54\x2c\x62\x0d"
>            "\xee\x04\x5b\x9d\x73\xf4\xcc\x29\x37\x01\xc2\x35\x8d\x3c"
>            "\x8a\x2f\xe3\xf5\x55\x42\x77\x55\x2d\x49\x6f\x46\xf7\x34"
>            "\xb1\x5f\xe7\x98\x55\xb5\x7c\x4e\xd7\x47\x18\xd1\xf9\xf2"
>            "\xd2\xfe\x47\xff\x22\x04\xa9\x32\xe9\xd6\x28\xda\xe1\x85"
>            "\xcb\xc5\xe6\xc1\xca\x9e\x3f\x1f\x80\xe6",
>            248);
>     r[10] = syscall(SYS_write, r[1], 0x20007000ul, 0xf8ul, 0, 0, 0);
>     break;
>   }
>   return 0;
> }
> 
> int main()
> {
>   long i;
>   pthread_t th[4];
> 
>   memset(r, -1, sizeof(r));
>   for (i = 0; i < 4; i++) {
>     pthread_create(&th[i], 0, thr, (void*)i);
>     usleep(10000);
>   }
>   for (i = 0; i < 4; i++) {
>     pthread_create(&th[i], 0, thr, (void*)i);
>     if (i % 2 == 0)
>       usleep(10000);
>   }
>   usleep(100000);
>   return 0;
> }
> 
> On commit 30f05309bde49295e02e45c7e615f73aa4e0ccc2.

Could you check the patch below?  It's untested yet in my side due to
other bugs...


thanks,

Takashi

---
diff --git a/sound/core/seq/seq_virmidi.c b/sound/core/seq/seq_virmidi.c
index 3da2d48610b3..1d13057c84cf 100644
--- a/sound/core/seq/seq_virmidi.c
+++ b/sound/core/seq/seq_virmidi.c
@@ -160,8 +160,11 @@ static void snd_virmidi_output_trigger(struct snd_rawmidi_substream *substream,
 		vmidi->trigger = 1;
 		if (vmidi->seq_mode == SNDRV_VIRMIDI_SEQ_DISPATCH &&
 		    !(vmidi->rdev->flags & SNDRV_VIRMIDI_SUBSCRIBE)) {
-			snd_rawmidi_transmit_ack(substream, substream->runtime->buffer_size - substream->runtime->avail);
-			return;		/* ignored */
+			while (snd_rawmidi_transmit(substream, buf,
+						    sizeof(buf)) > 0) {
+				/* ignored */
+			}
+			return;
 		}
 		if (vmidi->event.type != SNDRV_SEQ_EVENT_NONE) {
 			if (snd_seq_kernel_client_dispatch(vmidi->client, &vmidi->event, in_atomic(), 0) < 0)