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[93.158.190.104]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43f235a5d31sm17305755e9.35.2025.04.09.07.11.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 09 Apr 2025 07:11:38 -0700 (PDT) Message-ID: <3e245617-81a5-4ea3-843f-b86261cf8599@gmail.com> Date: Wed, 9 Apr 2025 16:10:58 +0200 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/3] kasan: Avoid sleepable page allocation from atomic context To: Alexander Gordeev , Andrew Morton Cc: Hugh Dickins , Nicholas Piggin , Guenter Roeck , Juergen Gross , Jeremy Fitzhardinge , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, stable@vger.kernel.org References: <2d9f4ac4528701b59d511a379a60107fa608ad30.1744128123.git.agordeev@linux.ibm.com> Content-Language: en-US From: Andrey Ryabinin In-Reply-To: <2d9f4ac4528701b59d511a379a60107fa608ad30.1744128123.git.agordeev@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/8/25 6:07 PM, Alexander Gordeev wrote: > apply_to_page_range() enters lazy MMU mode and then invokes > kasan_populate_vmalloc_pte() callback on each page table walk > iteration. The lazy MMU mode may only be entered only under > protection of the page table lock. However, the callback can > go into sleep when trying to allocate a single page. > > Change __get_free_page() allocation mode from GFP_KERNEL to > GFP_ATOMIC to avoid scheduling out while in atomic context. > > Cc: stable@vger.kernel.org > Fixes: 3c5c3cfb9ef4 ("kasan: support backing vmalloc space with real shadow memory") > Signed-off-by: Alexander Gordeev > --- > mm/kasan/shadow.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c > index 88d1c9dcb507..edfa77959474 100644 > --- a/mm/kasan/shadow.c > +++ b/mm/kasan/shadow.c > @@ -301,7 +301,7 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr, > if (likely(!pte_none(ptep_get(ptep)))) > return 0; > > - page = __get_free_page(GFP_KERNEL); > + page = __get_free_page(GFP_ATOMIC); > if (!page) > return -ENOMEM; > I think a better way to fix this would be moving out allocation from atomic context. Allocate page prior to apply_to_page_range() call and pass it down to kasan_populate_vmalloc_pte(). Whenever kasan_populate_vmalloc_pte() will require additional page we could bail out with -EAGAIN, and allocate another one.