linux-kernel - Re: [RFC-PATCH 1/2] mm: Add __GFP_NO

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Message-ID: <20200813183121.GY2674@hirez.programming.kicks-ass.net>
Date:   Thu, 13 Aug 2020 20:31:21 +0200
From:   peterz@...radead.org
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Michal Hocko <mhocko@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Uladzislau Rezki <urezki@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Joel Fernandes <joel@...lfernandes.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag

On Thu, Aug 13, 2020 at 09:29:04AM -0700, Paul E. McKenney wrote:
> OK.  So the current situation requires a choice between these these
> alternatives, each of which has shortcomings that have been mentioned
> earlier in this thread:
> 
> 1.	Prohibit invoking allocators from raw atomic context, such
> 	as when holding a raw spinlock.

This! This has always been the case, why are we even considering change
here?

> 2.	Adding a GFP_ flag.

The patch 1/2 in this thread is horrendous crap.

> 3.	Reusing existing GFP_ flags/values/whatever to communicate
> 	the raw-context information that was to be communicated by
> 	the new GFP_ flag.
> 
> 4.	Making lockdep forgive acquiring spinlocks while holding
> 	raw spinlocks, but only in CONFIG_PREEMPT_NONE=y kernels.
> 
> Am I missing anything?

How would 4 solve anything?


In other words, what is the actual friggin problem? I've not seen one
described anywhere.