Patchwork Oops with 2.6.29-rc7 on POWER5

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Submitter Benjamin Herrenschmidt
Date March 10, 2009, 12:36 a.m.
Message ID <1236645375.7260.200.camel@pasglop>
Download mbox | patch
Permalink /patch/24237/
State Accepted, archived
Headers show

Comments

Benjamin Herrenschmidt - March 10, 2009, 12:36 a.m.
On Mon, 2009-03-09 at 20:05 -0400, Josh Boyer wrote:
> [c00000000fffb830] [c0000000005fe504] .mutex_lock_nested+0x78/0x4b0
> (unreliable)
> [c00000000fffb950] [c00000000039d520] .echo_char_raw+0x40/0x98
> [c00000000fffb9f0] [c00000000039fd68] .n_tty_receive_buf+0xb48/0x1104
> [c00000000fffbbb0] [c0000000003a3a08] .flush_to_ldisc+0x160/0x244
> [c00000000fffbc80] [c0000000003a3b5c] .tty_flip_buffer_push+0x70/0x9c
> [c00000000fffbd10] [c0000000003b9e94] .hvsi_interrupt+0x464/0x590
> [c00000000fffbe50] [c000000000119168] .handle_IRQ_event+0x60/0xdc
> [c00000000fffbef0] [c00000000011baf0] .handle_fasteoi_irq+0x108/0x1a8
> 
Do that patch help ?

Alan, any comment about the races talked about in those comments ? Are
they still something I should worry about ?

hvc: Remove tty->low_latency on pseries backends

The hvcs and hvsi backends both set tty->low_latency to one, along
with more or less scary comments regarding bugs or races that would
happen if not doing so.

However, they also both call tty_flip_buffer_push() in conexts where
it's illegal to do so since some recent tty changes (or at least it
may have been illegal always but it nows blows) when low_latency is
set (ie, hard interrupt or with spinlock held and irqs disabled).

This removes the setting for now to get them back to working condition,
we'll have to address the races described in the comments separately
if they are still an issue (some of this might have been fixed already).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---
Josh Boyer - March 10, 2009, 11:43 a.m.
On Tue, Mar 10, 2009 at 11:36:15AM +1100, Benjamin Herrenschmidt wrote:
>On Mon, 2009-03-09 at 20:05 -0400, Josh Boyer wrote:
>> [c00000000fffb830] [c0000000005fe504] .mutex_lock_nested+0x78/0x4b0
>> (unreliable)
>> [c00000000fffb950] [c00000000039d520] .echo_char_raw+0x40/0x98
>> [c00000000fffb9f0] [c00000000039fd68] .n_tty_receive_buf+0xb48/0x1104
>> [c00000000fffbbb0] [c0000000003a3a08] .flush_to_ldisc+0x160/0x244
>> [c00000000fffbc80] [c0000000003a3b5c] .tty_flip_buffer_push+0x70/0x9c
>> [c00000000fffbd10] [c0000000003b9e94] .hvsi_interrupt+0x464/0x590
>> [c00000000fffbe50] [c000000000119168] .handle_IRQ_event+0x60/0xdc
>> [c00000000fffbef0] [c00000000011baf0] .handle_fasteoi_irq+0x108/0x1a8
>> 
>Do that patch help ?

Yes.  No more oopses on the hvc console when I hit 'enter'.

>Alan, any comment about the races talked about in those comments ? Are
>they still something I should worry about ?

If not, we should look at getting this into 2.6.29.  I know it's getting
very late, but having kernels oops whenever someone hits enter on the
console probably isn't very good either.

josh

Patch

Index: linux-work/drivers/char/hvcs.c
===================================================================
--- linux-work.orig/drivers/char/hvcs.c	2009-03-10 11:28:03.000000000 +1100
+++ linux-work/drivers/char/hvcs.c	2009-03-10 11:28:08.000000000 +1100
@@ -1139,15 +1139,6 @@  static int hvcs_open(struct tty_struct *
 	hvcsd->tty = tty;
 	tty->driver_data = hvcsd;
 
-	/*
-	 * Set this driver to low latency so that we actually have a chance at
-	 * catching a throttled TTY after we flip_buffer_push.  Otherwise the
-	 * flush_to_async may not execute until after the kernel_thread has
-	 * yielded and resumed the next flip_buffer_push resulting in data
-	 * loss.
-	 */
-	tty->low_latency = 1;
-
 	memset(&hvcsd->buffer[0], 0x00, HVCS_BUFF_LEN);
 
 	/*
Index: linux-work/drivers/char/hvsi.c
===================================================================
--- linux-work.orig/drivers/char/hvsi.c	2009-03-10 11:27:19.000000000 +1100
+++ linux-work/drivers/char/hvsi.c	2009-03-10 11:27:22.000000000 +1100
@@ -810,7 +810,6 @@  static int hvsi_open(struct tty_struct *
 	hp = &hvsi_ports[line];
 
 	tty->driver_data = hp;
-	tty->low_latency = 1; /* avoid throttle/tty_flip_buffer_push race */
 
 	mb();
 	if (hp->state == HVSI_FSP_DIED)