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