linux-kernel - Re: [PATCH v3] lockdep: Teach lockdep about memalloc_noio

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Date:   Wed, 1 Mar 2017 17:01:23 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nikolay Borisov <nborisov@...e.com>
Cc:     linux-kernel@...r.kernel.org, mhocko@...nel.org,
        vbabka.lkml@...il.com, linux-mm@...ck.org, mingo@...hat.com
Subject: Re: [PATCH v3] lockdep: Teach lockdep about memalloc_noio_save

On Wed, Mar 01, 2017 at 04:46:59PM +0100, Peter Zijlstra wrote:
> On Wed, Mar 01, 2017 at 01:29:57PM +0200, Nikolay Borisov wrote:
> > Commit 21caf2fc1931 ("mm: teach mm by current context info to not do I/O
> > during memory allocation") added the memalloc_noio_(save|restore) functions
> > to enable people to modify the MM behavior by disbaling I/O during memory
> > allocation. This was further extended in Fixes: 934f3072c17c ("mm: clear 
> > __GFP_FS when PF_MEMALLOC_NOIO is set"). memalloc_noio_* functions prevent 
> > allocation paths recursing back into the filesystem without explicitly 
> > changing the flags for every allocation site. However, lockdep hasn't been 
> > keeping up with the changes and it entirely misses handling the memalloc_noio
> > adjustments. Instead, it is left to the callers of __lockdep_trace_alloc to 
> > call the functino after they have shaven the respective GFP flags. 
> > 
> > Let's fix this by making lockdep explicitly do the shaving of respective
> > GFP flags. 
> 
> I edited that to look like the below, then my compiler said:
> 
> ../kernel/locking/lockdep.c: In function ‘lockdep_set_current_reclaim_state’:
> ../kernel/locking/lockdep.c:3866:33: error: implicit declaration of function ‘memalloc_noio_flags’ [-Werror=implicit-function-declaration]
>   current->lockdep_reclaim_gfp = memalloc_noio_flags(gfp_mask);
>                                  ^~~~~~~~~~~~~~~~~~~
> cc1: some warnings being treated as errors
> ../scripts/Makefile.build:294: recipe for target 'kernel/locking/lockdep.o' failed
> 

OK, its because Ingo moved crud around.

Ingo, this patch ought to go in tip/locking/core where it will actually
compile, but once you merge that sched.h header mucking in things go
*boom*.

How do you want this?