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Wed, 12 Feb 2025 09:52:43 -0800 (PST) Message-ID: Date: Wed, 12 Feb 2025 18:52:39 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] kasan: Don't call find_vm_area() in RT kernel To: Waiman Long Cc: Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , Andrew Morton , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, Nico Pache References: <20250211160750.1301353-1-longman@redhat.com> Content-Language: en-US From: Andrey Ryabinin In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 2/12/25 2:34 PM, Waiman Long wrote: > > On 2/12/25 6:59 AM, Andrey Ryabinin wrote: >> On Tue, Feb 11, 2025 at 5:08 PM Waiman Long wrote: >>> diff --git a/mm/kasan/report.c b/mm/kasan/report.c >>> index 3fe77a360f1c..e1ee687966aa 100644 >>> --- a/mm/kasan/report.c >>> +++ b/mm/kasan/report.c >>> @@ -398,9 +398,20 @@ static void print_address_description(void *addr, u8 tag, >>>                  pr_err("\n"); >>>          } >>> >>> -       if (is_vmalloc_addr(addr)) { >>> -               struct vm_struct *va = find_vm_area(addr); >>> +       if (!is_vmalloc_addr(addr)) >>> +               goto print_page; >>> >>> +       /* >>> +        * RT kernel cannot call find_vm_area() in atomic context. >>> +        * For !RT kernel, prevent spinlock_t inside raw_spinlock_t warning >>> +        * by raising wait-type to WAIT_SLEEP. >>> +        */ >>> +       if (!IS_ENABLED(CONFIG_PREEMPT_RT)) { >>> +               static DEFINE_WAIT_OVERRIDE_MAP(vmalloc_map, LD_WAIT_SLEEP); >>> +               struct vm_struct *va; >>> + >>> +               lock_map_acquire_try(&vmalloc_map); >>> +               va = find_vm_area(addr); >> Can we hide all this logic behind some function like >> kasan_find_vm_area() which would return NULL for -rt? > Sure. We can certainly do that. >> >>>                  if (va) { >>>                          pr_err("The buggy address belongs to the virtual mapping at\n" >>>                                 " [%px, %px) created by:\n" >>> @@ -410,8 +421,13 @@ static void print_address_description(void *addr, u8 tag, >>> >>>                          page = vmalloc_to_page(addr); >> Or does vmalloc_to_page() secretly take  some lock somewhere so we >> need to guard it with this 'vmalloc_map' too? >> So my suggestion above wouldn't be enough, if that's the case. > > AFAICS, vmalloc_to_page() doesn't seem to take any lock.  Even if it takes another spinlock, it will still be under the vmalloc_map protection until lock_map_release() is called. > I meant to do something like bellow, which would leave vmalloc_to_page() out of vmalloc_map scope. That's why I raised this question. --- mm/kasan/report.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/mm/kasan/report.c b/mm/kasan/report.c index 3fe77a360f1c..f3683215f4ca 100644 --- a/mm/kasan/report.c +++ b/mm/kasan/report.c @@ -370,6 +370,20 @@ static inline bool init_task_stack_addr(const void *addr) sizeof(init_thread_union.stack)); } +static inline struct vm_struct *kasan_find_vm_area(void *addr) +{ + static DEFINE_WAIT_OVERRIDE_MAP(vmalloc_map, LD_WAIT_SLEEP); + struct vm_struct *va; + + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + return NULL; + + lock_map_acquire_try(&vmalloc_map); + va = find_vm_area(addr); + lock_map_release(&vmalloc_map); + return va; +} + static void print_address_description(void *addr, u8 tag, struct kasan_report_info *info) { @@ -399,8 +413,7 @@ static void print_address_description(void *addr, u8 tag, } if (is_vmalloc_addr(addr)) { - struct vm_struct *va = find_vm_area(addr); - + struct vm_area *va = kasan_find_vm_area(addr); if (va) { pr_err("The buggy address belongs to the virtual mapping at\n" " [%px, %px) created by:\n" -- 2.45.3