linux-kernel - Re: [PATCH 0/9] Add blockconsole version 1.1 (try 2)

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Date:	Thu, 07 Mar 2013 19:46:50 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Jörn Engel <joern@...fs.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>, Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [PATCH 0/9] Add blockconsole version 1.1 (try 2)

At Wed, 6 Mar 2013 14:49:50 -0500,
Jörn Engel wrote:
> 
> On Tue, 5 March 2013 18:36:41 +0100, Takashi Iwai wrote:
> > 
> > Another thing I noticed is that the panic handler calls bcon_write(),
> > and it doesn't write to the device by itself.  Is it really supposed
> > to work?
> 
> Clearly it is supposed to work.  In reality it sometimes does and
> sometimes does not.  Patches to improve the success rate are welcome.

What I thought is to driver submit_bio in the panic handler itself
so that no scheduling is involved, like the patch below.  But I'm not
sure whether it would actually work...

> 
> > Meanwhile I hacked the code to allow it being built as a module.
> > If anyone is interested, I'll send a patch series.  It's pretty
> > hackish, so likely need more brush up, though.
> 
> I am interested.

OK, I'll send a patch series.  It'll be built on top of my previous
patches.  And I wrote it after merging to 3.9-rc1, so might be
slightly fuzzy to your tree.


thanks,

Takashi

---
diff --git a/drivers/block/blockconsole.c b/drivers/block/blockconsole.c
index 5fc192a..5042a5a 100644
--- a/drivers/block/blockconsole.c
+++ b/drivers/block/blockconsole.c
@@ -361,6 +361,16 @@ static void bcon_writesector(struct blockconsole *bc, int index)
 	submit_bio(WRITE, bio);
 }
 
+static void bcon_do_writeback(struct blockconsole *bc)
+{
+	while (bcon_write_sector(bc) != bcon_console_sector(bc)) {
+		bcon_writesector(bc, bcon_write_sector(bc));
+		bcon_advance_write_bytes(bc, SECTOR_SIZE);
+		if (bcon_write_sector(bc) == 0)
+			bcon_erase_segment(bc);
+	}
+}
+
 static int bcon_writeback(void *_bc)
 {
 	struct blockconsole *bc = _bc;
@@ -373,12 +383,7 @@ static int bcon_writeback(void *_bc)
 		schedule();
 		if (kthread_should_stop())
 			break;
-		while (bcon_write_sector(bc) != bcon_console_sector(bc)) {
-			bcon_writesector(bc, bcon_write_sector(bc));
-			bcon_advance_write_bytes(bc, SECTOR_SIZE);
-			if (bcon_write_sector(bc) == 0)
-				bcon_erase_segment(bc);
-		}
+		bcon_do_writeback(bc);
 	}
 	return 0;
 }
@@ -476,7 +481,7 @@ static int blockconsole_panic(struct notifier_block *this, unsigned long event,
 	n = SECTOR_SIZE - bcon_console_ofs(bc);
 	if (n != SECTOR_SIZE)
 		bcon_advance_console_bytes(bc, n);
-	bcon_writeback(bc);
+	bcon_do_writeback(bc);
 	return NOTIFY_DONE;
 }
 

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