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Fri, 04 Jul 2025 06:09:13 -0700 (PDT) Message-ID: Date: Fri, 4 Jul 2025 15:07:54 +0200 Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] kasan: remove kasan_find_vm_area() to prevent possible deadlock To: Andrey Konovalov , Yeoreum Yun Cc: glider@google.com, dvyukov@google.com, vincenzo.frascino@arm.com, akpm@linux-foundation.org, bigeasy@linutronix.de, clrkwllms@kernel.org, rostedt@goodmis.org, byungchul@sk.com, max.byungchul.park@gmail.com, ysk@kzalloc.com, kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev References: <20250703181018.580833-1-yeoreum.yun@arm.com> Content-Language: en-US From: Andrey Ryabinin In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 7/3/25 9:05 PM, Andrey Konovalov wrote: > On Thu, Jul 3, 2025 at 8:55 PM Yeoreum Yun wrote: >> >> Hi Andrey, >> >>>> >>>> find_vm_area() couldn't be called in atomic_context. >>>> If find_vm_area() is called to reports vm area information, >>>> kasan can trigger deadlock like: >>>> >>>> CPU0 CPU1 >>>> vmalloc(); >>>> alloc_vmap_area(); >>>> spin_lock(&vn->busy.lock) >>>> spin_lock_bh(&some_lock); >>>> >>>> >>>> spin_lock(&some_lock); >>>> >>>> kasan_report(); >>>> print_report(); >>>> print_address_description(); >>>> kasan_find_vm_area(); >>>> find_vm_area(); >>>> spin_lock(&vn->busy.lock) // deadlock! >>>> >>>> To prevent possible deadlock while kasan reports, remove kasan_find_vm_area(). >>> >>> Can we keep it for when we are in_task()? >> >> We couldn't do. since when kasan_find_vm_area() is called, >> the report_lock is grabbed with irq disabled. >> >> Please check discuss with Andrey Ryabinin: >> https://lore.kernel.org/all/4599f645-f79c-4cce-b686-494428bb9e2a@gmail.com/ > > That was about checking for !in_interrupt(), but I believe checking > for in_task() is different? But I'm not an expert on these checks. The problem is that CPU1 grabs '&vn->busy.lock' after the '&some_lock'. This could happen both in task and in irq contexts, so the in_task() guard just won't change anything.