From: Qian Cai <cai@lca.pw>
To: Michal Hocko <mhocko@kernel.org>
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
Date: Wed, 27 Mar 2019 07:34:32 -0400 [thread overview]
Message-ID: <651bd879-c8c0-b162-fee7-1e523904b14e@lca.pw> (raw)
In-Reply-To: <20190327084432.GA11927@dhcp22.suse.cz>
On 3/27/19 4:44 AM, Michal Hocko wrote:
>> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
>> index a2d894d3de07..7f4545ab1f84 100644
>> --- a/mm/kmemleak.c
>> +++ b/mm/kmemleak.c
>> @@ -580,7 +580,16 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size,
>> struct rb_node **link, *rb_parent;
>> unsigned long untagged_ptr;
>>
>> - object = kmem_cache_alloc(object_cache, gfp_kmemleak_mask(gfp));
>> + /*
>> + * The tracked memory was allocated successful, if the kmemleak object
>> + * failed to allocate for some reasons, it ends up with the whole
>> + * kmemleak disabled, so try it harder.
>> + */
>> + gfp = (in_atomic() || irqs_disabled()) ?
>> + gfp_kmemleak_mask(gfp) | GFP_ATOMIC :
>> + gfp_kmemleak_mask(gfp) | __GFP_DIRECT_RECLAIM;
>
>
> The comment for in_atomic says:
> * Are we running in atomic context? WARNING: this macro cannot
> * always detect atomic context; in particular, it cannot know about
> * held spinlocks in non-preemptible kernels. Thus it should not be
> * used in the general case to determine whether sleeping is possible.
> * Do not use in_atomic() in driver code.
That is why it needs both in_atomic() and irqs_disabled(), so irqs_disabled()
can detect kernel functions held spinlocks even in non-preemptible kernels.
According to [1],
"This [2] is useful if you know that the data in question is only ever
manipulated from a "process context", ie no interrupts involved."
Since kmemleak only deal with kernel context, if a spinlock was held, it always
has local interrupt disabled.
ftrace is in the same boat where this commit was merged a while back that has
the same check.
ef99b88b16be
tracing: Handle ftrace_dump() atomic context in graph_trace_open()
[1] https://www.kernel.org/doc/Documentation/locking/spinlocks.txt
[2]
spin_lock(&lock);
...
spin_unlock(&lock);
next prev parent reply other threads:[~2019-03-27 11:34 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-27 0:59 [PATCH v4] kmemleak: survive in a low-memory situation Qian Cai
2019-03-27 8:44 ` Michal Hocko
2019-03-27 11:34 ` Qian Cai [this message]
2019-03-27 11:44 ` Michal Hocko
2019-03-27 13:05 ` Qian Cai
2019-03-27 13:17 ` Michal Hocko
2019-03-27 17:29 ` Catalin Marinas
2019-03-27 18:02 ` Qian Cai
2019-03-28 15:05 ` Catalin Marinas
2019-03-28 15:41 ` Qian Cai
2019-03-27 18:17 ` Michal Hocko
2019-03-27 18:21 ` Matthew Wilcox
2019-03-28 14:59 ` Catalin Marinas
2019-03-28 15:24 ` Qian Cai
2019-03-29 12:02 ` Michal Hocko
2019-03-29 16:16 ` Catalin Marinas
2019-04-01 20:12 ` Michal Hocko
2019-04-05 16:43 ` Catalin Marinas
2019-03-28 6:05 ` Pekka Enberg
2019-03-28 10:30 ` Catalin Marinas
2019-03-28 11:50 ` Pekka Enberg
2019-03-28 15:28 ` Catalin Marinas
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