Re: [PATCH v2] kasan: Don't call find_vm_area() in RT kernel

[Waiman Long <llong@redhat.com>]

On 2/12/25 8:48 PM, Andrey Konovalov wrote:
> On Wed, Feb 12, 2025 at 5:22 PM Waiman Long <longman@redhat.com> wrote:
>> The following bug report appeared with a test run in a RT debug kernel.
>>
>> [ 3359.353842] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
>> [ 3359.353848] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 140605, name: kunit_try_catch
>> [ 3359.353853] preempt_count: 1, expected: 0
>>    :
>> [ 3359.353933] Call trace:
>>    :
>> [ 3359.353955]  rt_spin_lock+0x70/0x140
>> [ 3359.353959]  find_vmap_area+0x84/0x168
>> [ 3359.353963]  find_vm_area+0x1c/0x50
>> [ 3359.353966]  print_address_description.constprop.0+0x2a0/0x320
>> [ 3359.353972]  print_report+0x108/0x1f8
>> [ 3359.353976]  kasan_report+0x90/0xc8
>> [ 3359.353980]  __asan_load1+0x60/0x70
>>
>> Commit e30a0361b851 ("kasan: make report_lock a raw spinlock")
>> changes report_lock to a raw_spinlock_t to avoid a similar RT problem.
>> The print_address_description() function is called with report_lock
>> acquired and interrupt disabled.  However, the find_vm_area() function
>> still needs to acquire a spinlock_t which becomes a sleeping lock in
>> the RT kernel. IOW, we can't call find_vm_area() in a RT kernel and
>> changing report_lock to a raw_spinlock_t is not enough to completely
>> solve this RT kernel problem.
>>
>> Fix this bug report by skipping the find_vm_area() call in this case
>> and just print out the address as is.
>>
>> For !RT kernel, follow the example set in commit 0cce06ba859a
>> ("debugobjects,locking: Annotate debug_object_fill_pool() wait type
>> violation") and use DEFINE_WAIT_OVERRIDE_MAP() to avoid a spinlock_t
>> inside raw_spinlock_t warning.
> Would it be possible to get lockdep to allow taking spinlock_t inside
> raw_spinlock_t instead of annotating the callers for the !RT case? Or
> is this a rare thing for this to be allowed on !RT?
>
>> Fixes: e30a0361b851 ("kasan: make report_lock a raw spinlock")
>> Signed-off-by: Waiman Long <longman@redhat.com>
>> ---
>>   mm/kasan/report.c | 47 ++++++++++++++++++++++++++++++++++-------------
>>   1 file changed, 34 insertions(+), 13 deletions(-)
>>
>>   [v2] Encapsulate the change into a new
>>        kasan_print_vmalloc_info_ret_page() helper
>>
>> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
>> index 3fe77a360f1c..9580ac3f3203 100644
>> --- a/mm/kasan/report.c
>> +++ b/mm/kasan/report.c
>> @@ -370,6 +370,38 @@ static inline bool init_task_stack_addr(const void *addr)
>>                          sizeof(init_thread_union.stack));
>>   }
>>
>> +/*
>> + * 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.
>> + *
>> + * Return: page pointer or NULL
>> + */
>> +static inline struct page *kasan_print_vmalloc_info_ret_page(void *addr)
> No need for the kasan_ prefix: this is a static function. (Also the
> _ret_* suffix is something I've never seen before in the kernel
> context, but I don't mind it.)

Sorry for missing that. Yes, I can remove the prefix. Will post a v3.

Cheers,
Longman