[PATCH] ALSA: emu10k1: don't deadlock in proc-functions

[PATCH] ALSA: emu10k1: don't deadlock in proc-functions

[Michael Gernoth]

The functions snd_emu10k1_proc_spdif_read and snd_emu1010_fpga_read
acquire the emu_lock before accessing the FPGA. The function used
to access the FPGA (snd_emu1010_fpga_read) also tries to take
the emu_lock which causes a deadlock.
Remove the outer locking in the proc-functions (guarding only the
already safe fpga read) to prevent this deadlock.

Signed-off-by: Michael Gernoth <michael@gernoth.net>
---
 sound/pci/emu10k1/emuproc.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/sound/pci/emu10k1/emuproc.c b/sound/pci/emu10k1/emuproc.c
index 2ca9f2e..415d23c 100644
--- a/sound/pci/emu10k1/emuproc.c
+++ b/sound/pci/emu10k1/emuproc.c
@@ -245,27 +245,19 @@ static void snd_emu10k1_proc_spdif_read(struct snd_info_entry *entry,
 	u32 rate;
 
 	if (emu->card_capabilities->emu_model) {
-		spin_lock_irqsave(&emu->emu_lock, flags);
 		snd_emu1010_fpga_read(emu, 0x38, &value);
-		spin_unlock_irqrestore(&emu->emu_lock, flags);
 		if ((value & 0x1) == 0) {
-			spin_lock_irqsave(&emu->emu_lock, flags);
 			snd_emu1010_fpga_read(emu, 0x2a, &value);
 			snd_emu1010_fpga_read(emu, 0x2b, &value2);
-			spin_unlock_irqrestore(&emu->emu_lock, flags);
 			rate = 0x1770000 / (((value << 5) | value2)+1);	
 			snd_iprintf(buffer, "ADAT Locked : %u\n", rate);
 		} else {
 			snd_iprintf(buffer, "ADAT Unlocked\n");
 		}
-		spin_lock_irqsave(&emu->emu_lock, flags);
 		snd_emu1010_fpga_read(emu, 0x20, &value);
-		spin_unlock_irqrestore(&emu->emu_lock, flags);
 		if ((value & 0x4) == 0) {
-			spin_lock_irqsave(&emu->emu_lock, flags);
 			snd_emu1010_fpga_read(emu, 0x28, &value);
 			snd_emu1010_fpga_read(emu, 0x29, &value2);
-			spin_unlock_irqrestore(&emu->emu_lock, flags);
 			rate = 0x1770000 / (((value << 5) | value2)+1);	
 			snd_iprintf(buffer, "SPDIF Locked : %d\n", rate);
 		} else {
@@ -415,9 +407,7 @@ static void snd_emu_proc_emu1010_reg_read(struct snd_info_entry *entry,
 	snd_iprintf(buffer, "EMU1010 Registers:\n\n");
 
 	for(i = 0; i < 0x40; i+=1) {
-		spin_lock_irqsave(&emu->emu_lock, flags);
 		snd_emu1010_fpga_read(emu, i, &value);
-		spin_unlock_irqrestore(&emu->emu_lock, flags);
 		snd_iprintf(buffer, "%02X: %08X, %02X\n", i, value, (value >> 8) & 0x7f);
 	}
 }
-- 
2.1.4

Re: [PATCH] ALSA: emu10k1: don't deadlock in proc-functions

[Takashi Iwai]

At Thu, 9 Apr 2015 23:42:15 +0200,
Michael Gernoth wrote:
> 
> The functions snd_emu10k1_proc_spdif_read and snd_emu1010_fpga_read
> acquire the emu_lock before accessing the FPGA. The function used
> to access the FPGA (snd_emu1010_fpga_read) also tries to take
> the emu_lock which causes a deadlock.
> Remove the outer locking in the proc-functions (guarding only the
> already safe fpga read) to prevent this deadlock.
> 
> Signed-off-by: Michael Gernoth <michael@gernoth.net>

Oh, this is a really old bug.  Thanks for spotting out.
Applied now with additional fixes (removing superfluous flags
variables causing compile warnings).


Takashi

> ---
>  sound/pci/emu10k1/emuproc.c | 10 ----------
>  1 file changed, 10 deletions(-)
> 
> diff --git a/sound/pci/emu10k1/emuproc.c b/sound/pci/emu10k1/emuproc.c
> index 2ca9f2e..415d23c 100644
> --- a/sound/pci/emu10k1/emuproc.c
> +++ b/sound/pci/emu10k1/emuproc.c
> @@ -245,27 +245,19 @@ static void snd_emu10k1_proc_spdif_read(struct snd_info_entry *entry,
>  	u32 rate;
>  
>  	if (emu->card_capabilities->emu_model) {
> -		spin_lock_irqsave(&emu->emu_lock, flags);
>  		snd_emu1010_fpga_read(emu, 0x38, &value);
> -		spin_unlock_irqrestore(&emu->emu_lock, flags);
>  		if ((value & 0x1) == 0) {
> -			spin_lock_irqsave(&emu->emu_lock, flags);
>  			snd_emu1010_fpga_read(emu, 0x2a, &value);
>  			snd_emu1010_fpga_read(emu, 0x2b, &value2);
> -			spin_unlock_irqrestore(&emu->emu_lock, flags);
>  			rate = 0x1770000 / (((value << 5) | value2)+1);	
>  			snd_iprintf(buffer, "ADAT Locked : %u\n", rate);
>  		} else {
>  			snd_iprintf(buffer, "ADAT Unlocked\n");
>  		}
> -		spin_lock_irqsave(&emu->emu_lock, flags);
>  		snd_emu1010_fpga_read(emu, 0x20, &value);
> -		spin_unlock_irqrestore(&emu->emu_lock, flags);
>  		if ((value & 0x4) == 0) {
> -			spin_lock_irqsave(&emu->emu_lock, flags);
>  			snd_emu1010_fpga_read(emu, 0x28, &value);
>  			snd_emu1010_fpga_read(emu, 0x29, &value2);
> -			spin_unlock_irqrestore(&emu->emu_lock, flags);
>  			rate = 0x1770000 / (((value << 5) | value2)+1);	
>  			snd_iprintf(buffer, "SPDIF Locked : %d\n", rate);
>  		} else {
> @@ -415,9 +407,7 @@ static void snd_emu_proc_emu1010_reg_read(struct snd_info_entry *entry,
>  	snd_iprintf(buffer, "EMU1010 Registers:\n\n");
>  
>  	for(i = 0; i < 0x40; i+=1) {
> -		spin_lock_irqsave(&emu->emu_lock, flags);
>  		snd_emu1010_fpga_read(emu, i, &value);
> -		spin_unlock_irqrestore(&emu->emu_lock, flags);
>  		snd_iprintf(buffer, "%02X: %08X, %02X\n", i, value, (value >> 8) & 0x7f);
>  	}
>  }
> -- 
> 2.1.4
> 
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