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

[Michal Hocko <mhocko@kernel.org>]

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