Subject: Re: ALSA: pcm: use dma_can_mmap() to check if a device supports dma_mmap_*

From: Takashi Iwai <[email-masked]>
Date: Mon, 04 Nov 2019 09:02:41 +0100

On Mon, 04 Nov 2019 08:06:37 +0100,
youling 257 wrote:
> 
> This patch cause oops on android mainline kernel about gadget audio_source.
> Androidx86 run on android mainline kernel.
> 
> [ 385.104963] android_work: sent uevent USB_STATE=CONNECTED
> [ 385.109006] android_work: sent uevent USB_STATE=DISCONNECTED
> [ 385.182024] android_work: sent uevent USB_STATE=CONNECTED
> [ 385.184737] configfs-gadget gadget: high-speed config #1: b
> [ 385.184921] android_work: sent uevent USB_STATE=CONFIGURED
> [ 385.285268] BUG: kernel NULL pointer dereference, address: 0000000000000220
> [ 385.285339] #PF: supervisor read access in kernel mode
> [ 385.285374] #PF: error_code(0x0000) - not-present page
> [ 385.285436] PGD 80000000791e6067 P4D 80000000791e6067 PUD 0
> [ 385.285473] Oops: 0000 [#1] PREEMPT SMP PTI
> [ 385.285509] CPU: 0 PID: 5780 Comm: Binder:1383_5 Tainted: G O
> 5.4.0-rc6-android-x86_64+ #1
> [ 385.285571] Hardware name: Insyde ONDA Tablet/ONDA Tablet, BIOS
> ONDA.D890HBBNR0A 03/11/2015
> [ 385.285639] RIP: 0010:dma_can_mmap+0x5/0x30
> [ 385.285675] Code: 74 11 e9 ae 98 b2 00 48 8b 05 9f 40 94 01 48 85 c0
> 75 e3 31 c0 c3 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 0f 1f 44
> 00 00 <48> 8b 87 20 02 00 00 48 85 c0 74 09 48 83 78 10 00 0f 95 c0 c3
> 48
> [ 385.285762] RSP: 0018:ffffb39443b63b78 EFLAGS: 00010246
> [ 385.285797] RAX: 0000000000000001 RBX: ffffa28b91756600 RCX: 0000000000000040
> [ 385.285857] RDX: ffffffffb62b2a00 RSI: 0000000000000000 RDI: 0000000000000000
> [ 385.285917] RBP: ffffa28bac69f800 R08: ffffffffb63141b0 R09: ffffa28bf9a34a88
> [ 385.285952] R10: ffffffffb62b2be0 R11: ffffffffb62b2bd0 R12: 0000000000000008
> [ 385.286013] R13: 0000000000000000 R14: ffffa28bacd736a8 R15: ffffa28bacd736c8
> [ 385.286076] FS: 0000000000000000(0000) GS:ffffa28bfb600000(0063)
> knlGS:00000000f5d81970
> [ 385.286110] CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033
> [ 385.286171] CR2: 0000000000000220 CR3: 000000007b2f6000 CR4: 00000000001006f0
> [ 385.286232] Call Trace:
> [ 385.286275] snd_pcm_hw_constraints_complete+0x3e/0x1f0
> [ 385.286314] snd_pcm_open_substream+0x94/0x140
> [ 385.286377] snd_pcm_open+0xf0/0x240
> [ 385.286416] ? wake_up_q+0x60/0x60
> [ 385.286460] snd_pcm_playback_open+0x3d/0x60
> [ 385.286533] chrdev_open+0xa2/0x1c0
> [ 385.286574] ? cdev_put.part.0+0x20/0x20
> [ 385.286615] do_dentry_open+0x13a/0x380
> [ 385.286686] path_openat+0x588/0x15d0
> [ 385.286728] do_filp_open+0x91/0x100
> [ 385.286769] ? __check_object_size+0x136/0x147
> [ 385.286840] do_sys_open+0x184/0x280
> [ 385.286880] ? handle_mm_fault+0xd7/0x1c0
> [ 385.286920] do_fast_syscall_32+0x8e/0x250
> [ 385.286992] entry_SYSENTER_compat+0x7c/0x8e
> 
> [ 385.287302] CR2: 0000000000000220
> [ 385.287391] ---[ end trace 73ffcefcbbe2b9a0 ]---

Exactly which driver is hit?  The code path is via hw_support_mmap()
and it's currently:

static bool hw_support_mmap(struct snd_pcm_substream *substream)
{
	if (!(substream->runtime->hw.info & SNDRV_PCM_INFO_MMAP))
		return false;

	if (substream->ops->mmap ||
	    substream->dma_buffer.dev.type != SNDRV_DMA_TYPE_DEV)
		return true;

	return dma_can_mmap(substream->dma_buffer.dev.dev);
}

so at least the driver has already set the SNDRV_DMA_TYPE_DEV
explicitly (it's non-zero) and some device object, but the device
object was invalid for dma_can_mmap() call.

This smells more like a driver-side issue, not in the core side.

thanks,

Takashi

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