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([2402:f000:1:1501:200:5efe:a66f:460b]) by smtp.gmail.com with ESMTPSA id z18-v6sm4817763pgc.0.2018.06.20.20.47.00 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 20 Jun 2018 20:47:02 -0700 (PDT) Subject: Re: [PATCH] mm: mempool: Fix a possible sleep-in-atomic-context bug in mempool_resize() To: Matthew Wilcox Cc: akpm@linux-foundation.org, dvyukov@google.com, gregkh@linuxfoundation.org, jthumshirn@suse.de, pombredanne@nexb.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20180621030714.10368-1-baijiaju1990@gmail.com> <20180621033839.GB12608@bombadil.infradead.org> From: Jia-Ju Bai Message-ID: <7a900944-5281-2e07-54f9-fc7574d2c538@gmail.com> Date: Thu, 21 Jun 2018 11:46:33 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <20180621033839.GB12608@bombadil.infradead.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/6/21 11:38, Matthew Wilcox wrote: > On Thu, Jun 21, 2018 at 11:07:14AM +0800, Jia-Ju Bai wrote: >> The kernel may sleep with holding a spinlock. >> The function call path (from bottom to top) in Linux-4.16.7 is: >> >> [FUNC] remove_element(GFP_KERNEL) >> mm/mempool.c, 250: remove_element in mempool_resize >> mm/mempool.c, 247: _raw_spin_lock_irqsave in mempool_resize >> >> To fix this bug, GFP_KERNEL is replaced with GFP_ATOMIC. >> >> This bug is found by my static analysis tool (DSAC-2) and checked by >> my code review. > But ... we don't use the flags argument. > > static void *remove_element(mempool_t *pool, gfp_t flags) > { > void *element = pool->elements[--pool->curr_nr]; > > BUG_ON(pool->curr_nr < 0); > kasan_unpoison_element(pool, element, flags); > check_element(pool, element); > return element; > } > > ... > > static void kasan_unpoison_element(mempool_t *pool, void *element, gfp_t flags) > { > if (pool->alloc == mempool_alloc_slab || pool->alloc == mempool_kmalloc) > kasan_unpoison_slab(element); > if (pool->alloc == mempool_alloc_pages) > kasan_alloc_pages(element, (unsigned long)pool->pool_data); > } > > So the correct patch would just remove this argument to remove_element() and > kasan_unpoison_element()? Yes, I also find this. I can submit a patch that removes the flag in: Definitions of kasan_unpoison_element() and remove_element() Three calls to remove_element() and one call to kasan_unpoison_element() in mempool.c. Do you think it is okay? Best wishes, Jia-Ju Bai