Re: Linux 2.6.20-rc1

[Linus Torvalds]

On Fri, 15 Dec 2006, Alistair John Strachan wrote:
> 
> In total isolation, v2.6.19..0e75f9063f5c55fb0b0b546a7c356f8ec186825e it 
> breaks. Reverting just 0e75f9063f5c55fb0b0b546a7c356f8ec186825e, it works 
> again.
> 
> So I think this is the source, but I can't explain why it "goes away" before 
> git1 and "comes back" before 2.6.20-rc1.

Can you see if the kernel state at commit 77d172ce ("[PATCH] fix SG_IO bio 
leak") is good? Ie just do something like

	git checkout -b test-branch 77d172ce

and compile and test that?

That commit _should_ be the one that fixed whatever problems that commit 
0e75f906 introduced. It *did* fix it for other - somewhat similar - 
situations.

That said: Jens - I think 0e75f906 was a mistake. "blk_rq_unmap()" really 
should be passed the "struct bio", not the "struct request *". Right now 
it does something _really_ strange with requests with linked bio's, and I 
don't think your and FUJITA's "leak fix" really works. What happens when 
the bio was a linked list on the request, and you put the old _head_ on 
the request with "rq->bio = bio"? What happens to the other parts of it?

IOW, I think this is broken. I think we should revert 0e75f906. Or at 
least you should explain to me why it's not broken, and why clearly people 
(eg Alistair) still see problems with it?

		Linus
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