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From: Neil Brown on 2 Aug 2010 18:00
On Mon, 02 Aug 2010 16:15:38 +0200
Tejun Heo <tj(a)kernel.org> wrote:

> Commit a82afdf (block: use the same failfast bits for bio and request)
> moved BIO_RW_* bits around such that they match up with REQ_* bits.
> Unfortunately, fs.h hard coded READ, WRITE, READA and SWRITE as 0, 1,
> 2 and 3, and expected them to match with BIO_RW_* bits. READ/WRITE
> didn't change but BIO_RW_AHEAD was moved to bit 4 instead of bit 1,
> breaking READA and SWRITE.
>
> This patch updates READA and SWRITE such that they match the BIO_RW_*
> bits again. A follow up patch will update the definitions to directly
> use BIO_RW_* bits so that this kind of breakage won't happen again.
>
> Stable: The offending commit a82afdf was released with v2.6.32, so
> this patch should be applied to all kernels since then but it must
> _NOT_ be applied to kernels earlier than that.
>
> Signed-off-by: Tejun Heo <tj(a)kernel.org>
> Reported-and-bisected-by: Vladislav Bolkhovitin <vst(a)vlnb.net>
> Root-caused-by: Neil Brown <neilb(a)suse.de>
> Cc: Jens Axobe <axboe(a)kernel.dk>
> Cc: stable(a)kernel.org
> ---
> Aieee... thanks for root causing it Neil. That was a stupid bug. I
> knew that READ/WRITE were hardcoded but forgot about READA. :-(
> Moving BIO_RW_AHEAD back to bit 1 might be a better solution but I'm
> afraid that would cause more confusions downstream. This patch
> updates READA and SWRITE to match BIO_RW_AHEAD and should also appear
> in -stable releases. The next patch will create bio_types.h and
> define all constants in terms of BIO_RW_*.
>
> Thanks.
>
> (resending w/ Jens' new address)
>
> include/linux/fs.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> Index: work/include/linux/fs.h
> ===================================================================
> --- work.orig/include/linux/fs.h
> +++ work/include/linux/fs.h
> @@ -148,8 +148,8 @@ struct inodes_stat_t {
> #define RWA_MASK 2

Close, but not quite there - RWA_MASK must be 16 too !!

Thanks,
NeilBrown


> #define READ 0
> #define WRITE 1
> -#define READA 2 /* read-ahead - don't block if no resources */
> -#define SWRITE 3 /* for ll_rw_block() - wait for buffer lock */
> +#define READA 16 /* read-ahead - don't block if no resources */
> +#define SWRITE 17 /* for ll_rw_block() - wait for buffer lock */
> #define READ_SYNC (READ | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG))
> #define READ_META (READ | (1 << BIO_RW_META))
> #define WRITE_SYNC_PLUG (WRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_NOIDLE))

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From: Tejun Heo on 3 Aug 2010 05:30
On 08/02/2010 11:52 PM, Neil Brown wrote:
> Close, but not quite there - RWA_MASK must be 16 too !!

Indeed. Updated.

Thanks.

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tejun
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From: Vladislav Bolkhovitin on 5 Aug 2010 15:00

Jeff Moyer, on 08/05/2010 10:45 PM wrote:
> Tejun Heo<tj(a)kernel.org> writes:
>
>> Commit a82afdf (block: use the same failfast bits for bio and request)
>> moved BIO_RW_* bits around such that they match up with REQ_* bits.
>> Unfortunately, fs.h hard coded READ, WRITE, READA and SWRITE as 0, 1,
>> 2 and 3, and expected them to match with BIO_RW_* bits. READ/WRITE
>> didn't change but BIO_RW_AHEAD was moved to bit 4 instead of bit 1,
>> breaking READA and SWRITE.
>>
>> This patch updates READA and SWRITE such that they match the BIO_RW_*
>> bits again. A follow up patch will update the definitions to directly
>> use BIO_RW_* bits so that this kind of breakage won't happen again.
>>
>> Stable: The offending commit a82afdf was released with v2.6.32, so
>> this patch should be applied to all kernels since then but it must
>> _NOT_ be applied to kernels earlier than that.
>
> Would someone be so kind as to remind me how this problem manifests
> itself? I know I read this recently, but my memory and googling skills
> are both failing me. :(

See http://lkml.org/lkml/2010/7/28/315 and link inside.

Vlad
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From: Tao Ma on 6 Aug 2010 01:00
Hi Tejun,

On 08/06/2010 02:45 AM, Jeff Moyer wrote:
> Tejun Heo<tj(a)kernel.org> writes:
>
>> Commit a82afdf (block: use the same failfast bits for bio and request)
>> moved BIO_RW_* bits around such that they match up with REQ_* bits.
>> Unfortunately, fs.h hard coded READ, WRITE, READA and SWRITE as 0, 1,
>> 2 and 3, and expected them to match with BIO_RW_* bits. READ/WRITE
>> didn't change but BIO_RW_AHEAD was moved to bit 4 instead of bit 1,
>> breaking READA and SWRITE.
>>
>> This patch updates READA and SWRITE such that they match the BIO_RW_*
>> bits again. A follow up patch will update the definitions to directly
>> use BIO_RW_* bits so that this kind of breakage won't happen again.
>>
>> Stable: The offending commit a82afdf was released with v2.6.32, so
>> this patch should be applied to all kernels since then but it must
>> _NOT_ be applied to kernels earlier than that.
If only this patch goes into stable, do we need to change RWA_MASK in
this patch also(I have seen you change it the 2/2)?

-#define RWA_MASK 2
+#define RWA_MASK 16

Regards,
Tao

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From: Tejun Heo on 6 Aug 2010 02:40
Hello,

On 08/06/2010 06:04 AM, Tao Ma wrote:
> If only this patch goes into stable, do we need to change RWA_MASK in this patch also(I have seen you change it the 2/2)?
>
> -#define RWA_MASK 2
> +#define RWA_MASK 16

Yeah, Neil already pointed it out and updated patch has been posted
and merged.

Thanks.

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tejun
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