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From: Neil Brown <neilb@cse.unsw.edu.au>
To: Linus Torvalds <torvalds@transmeta.com>
Date: Wed, 13 Dec 2000 11:17:19 +1100 (EST)
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cc: Jasper Spaans <jasper@spaans.ds9a.nl>, linux-kernel@vger.kernel.org
Subject: Re: [BUG] raid5 crash with 2.4.0-test12 [Was: Linux-2.4.0-test12]
In-Reply-To: message from Linus Torvalds on Tuesday December 12
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On Tuesday December 12, torvalds@transmeta.com wrote:
> 
> 
> On Wed, 13 Dec 2000, Neil Brown wrote:
> >
> > Could you add this test to the top of md_make_request as well, because
> > requests to raid5 don't go through generic_make_request.
> 
> Sure they do. Everything that calls ll_rw_block() or submit_bh() will go
> through generic_make_request.
> 
> Neil, you're probably thinking about __make_request(), which only triggers
> for "normal" devices.

Yes... you are right.  Alright, I can't escape it any other way so I
guess I must admit that  it is a raid5 bug.

But how can raid5 be calling b_end_io on a buffer_head that was never
passed to generic_make_request?
Answer, it snoops on the buffer cache to try to do complete stripe
writes.
The following patch disabled that code.

NeilBrown

--- drivers/md/raid5.c	2000/12/13 00:13:54	1.1
+++ drivers/md/raid5.c	2000/12/13 00:14:07
@@ -1009,6 +1009,7 @@
 	struct buffer_head *bh;
 	int method1 = INT_MAX, method2 = INT_MAX;
 
+#if 0
 	/*
 	 * Attempt to add entries :-)
 	 */
@@ -1039,6 +1040,7 @@
 			atomic_dec(&bh->b_count);
 		}
 	}
+#endif
 	PRINTK("handle_stripe() -- begin writing, stripe %lu\n", sh->sector);
 	/*
 	 * Writing, need to update parity buffer.
 
-
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