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From: Jim Nelson <james4765@verizon.net>
To: Jan Dittmer <jdittmer@ppp0.net>
Cc: kernel-janitors@lists.osdl.org, linux-kernel@vger.kernel.org,
	akpm@osdl.org
Subject: [KJ] Re: [PATCH] esp: replace cli()/sti() with
Date: Sat, 18 Dec 2004 03:46:47 +0000	[thread overview]
Message-ID: <41C3A827.9090301@verizon.net> (raw)
In-Reply-To: <41C385FC.3010109@ppp0.net>

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Jan Dittmer wrote:
> James Nelson wrote:
> 
>>This is an attempt to make the esp driver SMP-correct.
> 
> 
> You're trying to protect the info data, correct? Could you please
> add a comment to the locks which data structures need to be
> protected by them?!
> Just blindly replacing cli/sti with spin_(un)lock doesn't make it
> SMP save.
> 

*sigh* Thought it wouldn't be that easy.



> 
>>diff -urN --exclude='*~' linux-2.6.10-rc3-mm1-original/drivers/char/esp.c linux-2.6.10-rc3-mm1/drivers/char/esp.c
>>--- linux-2.6.10-rc3-mm1-original/drivers/char/esp.c	2004-12-03 16:52:13.000000000 -0500
>>+++ linux-2.6.10-rc3-mm1/drivers/char/esp.c	2004-12-17 18:11:31.275037730 -0500
>>@@ -212,14 +214,14 @@
>> 	if (serial_paranoia_check(info, tty->name, "rs_stop"))
>> 		return;
>> 	
>>-	save_flags(flags); cli();
>>+	spin_lock_irqsave(&esp_lock, flags);
> 
> 
> info can change between return and lock
> 

Okay.  I see what you are talking about.  I'll dig into it tomorrow (after some 
sleep).

OTOH, this would have been SMP-incorrect even before cli()/sti() was dropped in 2.5 .

> 
>> 	if (info->IER & UART_IER_THRI) {
>> 		info->IER &= ~UART_IER_THRI;
>> 		serial_out(info, UART_ESI_CMD1, ESI_SET_SRV_MASK);
>> 		serial_out(info, UART_ESI_CMD2, info->IER);
>> 	}
>> 
>>-	restore_flags(flags);
>>+	spin_unlock_irqrestore(&esp_lock, flags);
>> }
>> 
>> static void rs_start(struct tty_struct *tty)
>>@@ -230,13 +232,13 @@
>> 	if (serial_paranoia_check(info, tty->name, "rs_start"))
>> 		return;
>> 	
>>-	save_flags(flags); cli();
>>+	spin_lock_irqsave(&esp_lock, flags);
> 
> 
> same here.
> 
> 
>> 	if (info->xmit_cnt && info->xmit_buf && !(info->IER & UART_IER_THRI)) {
>> 		info->IER |= UART_IER_THRI;
>> 		serial_out(info, UART_ESI_CMD1, ESI_SET_SRV_MASK);
>> 		serial_out(info, UART_ESI_CMD2, info->IER);
>> 	}
>>-	restore_flags(flags);
>>+	spin_unlock_irqrestore(&esp_lock, flags);
>> }
>> 
>> /*
> 
> 
> Didn't read the rest. Are you sure you didn't introduce a deadlock in
> the interrupt handler? {transmit,receiver}_chars_{pio,dma} also try to take
> the lock.
> 

Hm.  I made the assumption (silly me) that the code was inherently SMP-correct, 
and just needed the function calls replaced.

Live and learn.

Jim

> Jan
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 


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WARNING: multiple messages have this Message-ID (diff)
From: Jim Nelson <james4765@verizon.net>
To: Jan Dittmer <jdittmer@ppp0.net>
Cc: kernel-janitors@lists.osdl.org, linux-kernel@vger.kernel.org,
	akpm@osdl.org
Subject: Re: [PATCH] esp: replace cli()/sti() with spin_lock_irqsave()/spin_unlock_irqrestore()
Date: Fri, 17 Dec 2004 22:46:47 -0500	[thread overview]
Message-ID: <41C3A827.9090301@verizon.net> (raw)
In-Reply-To: <41C385FC.3010109@ppp0.net>

Jan Dittmer wrote:
> James Nelson wrote:
> 
>>This is an attempt to make the esp driver SMP-correct.
> 
> 
> You're trying to protect the info data, correct? Could you please
> add a comment to the locks which data structures need to be
> protected by them?!
> Just blindly replacing cli/sti with spin_(un)lock doesn't make it
> SMP save.
> 

*sigh* Thought it wouldn't be that easy.



> 
>>diff -urN --exclude='*~' linux-2.6.10-rc3-mm1-original/drivers/char/esp.c linux-2.6.10-rc3-mm1/drivers/char/esp.c
>>--- linux-2.6.10-rc3-mm1-original/drivers/char/esp.c	2004-12-03 16:52:13.000000000 -0500
>>+++ linux-2.6.10-rc3-mm1/drivers/char/esp.c	2004-12-17 18:11:31.275037730 -0500
>>@@ -212,14 +214,14 @@
>> 	if (serial_paranoia_check(info, tty->name, "rs_stop"))
>> 		return;
>> 	
>>-	save_flags(flags); cli();
>>+	spin_lock_irqsave(&esp_lock, flags);
> 
> 
> info can change between return and lock
> 

Okay.  I see what you are talking about.  I'll dig into it tomorrow (after some 
sleep).

OTOH, this would have been SMP-incorrect even before cli()/sti() was dropped in 2.5 .

> 
>> 	if (info->IER & UART_IER_THRI) {
>> 		info->IER &= ~UART_IER_THRI;
>> 		serial_out(info, UART_ESI_CMD1, ESI_SET_SRV_MASK);
>> 		serial_out(info, UART_ESI_CMD2, info->IER);
>> 	}
>> 
>>-	restore_flags(flags);
>>+	spin_unlock_irqrestore(&esp_lock, flags);
>> }
>> 
>> static void rs_start(struct tty_struct *tty)
>>@@ -230,13 +232,13 @@
>> 	if (serial_paranoia_check(info, tty->name, "rs_start"))
>> 		return;
>> 	
>>-	save_flags(flags); cli();
>>+	spin_lock_irqsave(&esp_lock, flags);
> 
> 
> same here.
> 
> 
>> 	if (info->xmit_cnt && info->xmit_buf && !(info->IER & UART_IER_THRI)) {
>> 		info->IER |= UART_IER_THRI;
>> 		serial_out(info, UART_ESI_CMD1, ESI_SET_SRV_MASK);
>> 		serial_out(info, UART_ESI_CMD2, info->IER);
>> 	}
>>-	restore_flags(flags);
>>+	spin_unlock_irqrestore(&esp_lock, flags);
>> }
>> 
>> /*
> 
> 
> Didn't read the rest. Are you sure you didn't introduce a deadlock in
> the interrupt handler? {transmit,receiver}_chars_{pio,dma} also try to take
> the lock.
> 

Hm.  I made the assumption (silly me) that the code was inherently SMP-correct, 
and just needed the function calls replaced.

Live and learn.

Jim

> Jan
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 


  reply	other threads:[~2004-12-18  3:46 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-12-17 23:18 [KJ] [PATCH] esp: replace cli()/sti() with James Nelson
2004-12-17 23:18 ` [PATCH] esp: replace cli()/sti() with spin_lock_irqsave()/spin_unlock_irqrestore() James Nelson
2004-12-18  1:21 ` [KJ] Re: [PATCH] esp: replace cli()/sti() with Jan Dittmer
2004-12-18  1:21   ` [PATCH] esp: replace cli()/sti() with spin_lock_irqsave()/spin_unlock_irqrestore() Jan Dittmer
2004-12-18  3:46   ` Jim Nelson [this message]
2004-12-18  3:46     ` Jim Nelson

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