linux-kernel - Re: [PATCH 1/5] percpu_ida: Make percpu_ida

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Message-ID: <1390191463.5567.760.camel@haakon3.risingtidesystems.com>
Date:	Sun, 19 Jan 2014 20:17:43 -0800
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	target-devel <target-devel@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Kent Overstreet <kmo@...erainc.com>,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 1/5] percpu_ida: Make percpu_ida_alloc accept task state
 bitmask

On Sun, 2014-01-19 at 18:38 -0800, Linus Torvalds wrote:
> On Sun, Jan 19, 2014 at 2:16 AM, Nicholas A. Bellinger
> <nab@...ux-iscsi.org> wrote:
> >
> > This patch changes percpu_ida_alloc() to accept task state bitmask
> > for prepare_to_wait() to support interruptible sleep for callers
> > that require it.
> 
> This patch-series is not bisectable. Afaik, the first patch will break
> the build (or at least cause the end result to not actually work).
> 
> This kind of "split up one large patch into many small patches THAT
> DON'T ACTUALLY WORK INDIVIDUALLY" model is pure and utter garbage.
> 
> So a big NAK on this series as being completely broken.
> 

So the late night reasoning was to allow the patches to apply cleanly to
stable.  That was, indeed, a bad decision.

> To fix it, I would suggest:
> 
>  - make the first patch change all *existing* users (that only have
> the atomic vs uninterruptible semantics) pass in either
> TASK_UNINTERRUPTIBLE or TASK_RUNNING depending on whether they had
> __GFP_WAIT or not.
> 
>    So the first patch would not change *any* semantics or behavior, it
> would only change the calling convention.
> 
>  - do the cleanup patches to block/blk-mq-tag.c to not have those
> "gfp" calling convention, and instead passing in the state natively
> 
>  - add the TASK_INTERRUPTIBLE case last (which includes the new
> "signal_pending_state()" logic in percpu_ida_alloc())
> 
> that way, all patches compile cleanly and should each work
> individually, and they all do clearly just one thing. And the biggest
> patch in the series (the first one) doesn't actually make any semantic
> changes.

-v2 sent out.  Please review.

Jens, please review the blk-mq specific changes in patch #1, and let me
know if you'd like to pick-up #2 via the block tree, or have it included
in target-pending/for-next.

Thanks,

--nab

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