linux-kernel - Re: [PATCH v4] kmemleak: survive in a low-memory situation

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Date:   Wed, 27 Mar 2019 14:17:18 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Qian Cai <cai@....pw>
Cc:     akpm@...ux-foundation.org, catalin.marinas@....com, cl@...ux.com,
        willy@...radead.org, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] kmemleak: survive in a low-memory situation

On Wed 27-03-19 09:05:31, Qian Cai wrote:
> On 3/27/19 7:44 AM, Michal Hocko wrote> What? Normal spin lock implementation
> doesn't disable interrupts. So
> > either I misunderstand what you are saying or you seem to be confused.
> > the thing is that in_atomic relies on preempt_count to work properly and
> > if you have CONFIG_PREEMPT_COUNT=n then you simply never know whether
> > preemption is disabled so you do not know that a spin_lock is held.
> > irqs_disabled on the other hand checks whether arch specific flag for
> > IRQs handling is set (or cleared). So you would only catch irq safe spin
> > locks with the above check.
> 
> Exactly, because kmemleak_alloc() is only called in a few call sites, slab
> allocation, neigh_hash_alloc(), alloc_page_ext(), sg_kmalloc(),
> early_amd_iommu_init() and blk_mq_alloc_rqs(), my review does not yield any of
> those holding irq unsafe spinlocks.

I do not understand. What about a regular kmalloc(GFP_NOWAIT) callers with a simple
spinlock held?

-- 
Michal Hocko
SUSE Labs