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Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i386, bisected, reproducable)

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From: Linus Torvalds <torvalds@...>
To: Andi Kleen <andi@...>
Cc: Bron Gondwana <brong@...>, Linux Kernel Mailing List <linux-kernel@...>, Nick Piggin <npiggin@...>, Andrew Morton <akpm@...>, Rob Mueller <robm@...>, Ingo Molnar <mingo@...>
Subject: Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i386, bisected, reproducable)
Date: Tuesday, June 17, 2008 - 5:14 pm

On Tue, 17 Jun 2008, Andi Kleen wrote:

That's not the problem, Andi.

The problem is that it returns THE WRONG VALUE!

If the fault happened on the second load, but the first load was never 
actually paired up with a store (because of unrolling the loop), then YOU 
MUST NOT CLAIM THAT YOU DID A 8-BYTE COPY! Because you have copied exactly 
_zero_ bytes, even though you _loaded_ 8 bytes successfully!

See?

Claiming that you copied 8 bytes when you didn't do anything at all is 
WRONG. It's so incredibly wrong that it is scary. 

			Linus
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Messages in current thread:
BUG: mmapfile/writev spurious zero bytes (x86_64/not i386, b..., Bron Gondwana, (Tue Jun 17, 2:00 am)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Bron Gondwana, (Tue Jun 17, 2:02 am)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Tue Jun 17, 1:08 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Bron Gondwana, (Tue Jun 17, 10:21 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Tue Jun 17, 1:45 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Tue Jun 17, 4:16 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Andi Kleen, (Tue Jun 17, 4:58 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Tue Jun 17, 5:14 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Andi Kleen, (Tue Jun 17, 5:26 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Tue Jun 17, 5:31 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Andi Kleen, (Tue Jun 17, 5:34 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Tue Jun 17, 5:46 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Nick Piggin, (Wed Jun 18, 2:10 am)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Tue Jun 17, 5:34 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Tue Jun 17, 4:41 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Andi Kleen, (Tue Jun 17, 5:15 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Tue Jun 17, 5:06 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Tue Jun 17, 5:20 pm)
BUG: mmapfile/writev spurious zero bytes still in the wild, Bron Gondwana, (Fri Oct 3, 7:44 am)
Re: BUG: mmapfile/writev spurious zero bytes still in the wild, Andrew Morton, (Fri Oct 3, 9:07 am)
Re: BUG: mmapfile/writev spurious zero bytes still in the wild, Bron Gondwana, (Fri Oct 3, 8:13 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Bron Gondwana, (Tue Jun 17, 11:14 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Wed Jun 18, 12:03 am)
Cyrus mmap vs lseek/write usage - (WAS: BUG: mmapfile/writev..., Bron Gondwana, (Wed Jun 18, 1:11 am)
Re: Cyrus mmap vs lseek/write usage - (WAS: BUG: mmapfile/wr..., Linus Torvalds, (Wed Jun 18, 12:22 pm)
Re: Cyrus mmap vs lseek/write usage - (WAS: BUG: mmapfile/wr..., Robert Mueller, (Wed Jun 18, 7:45 pm)
Re: Cyrus mmap vs lseek/write usage - (WAS: BUG: mmapfile/wr..., Linus Torvalds, (Wed Jun 18, 8:20 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Bron Gondwana, (Tue Jun 17, 10:27 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Andi Kleen, (Tue Jun 17, 5:16 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Tue Jun 17, 5:24 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Al Viro, (Tue Jun 17, 5:36 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Andi Kleen, (Tue Jun 17, 5:42 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Al Viro, (Tue Jun 17, 6:11 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Andi Kleen, (Tue Jun 17, 6:21 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i386,, Nick Piggin, (Wed Jun 18, 2:22 am)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Tue Jun 17, 5:49 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Andi Kleen, (Tue Jun 17, 5:30 pm)
Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i38..., Linus Torvalds, (Tue Jun 17, 5:37 pm)