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

[Waiman Long <llong@redhat.com>]

On 2/11/25 5:57 PM, Andrew Morton wrote:
> On Tue, 11 Feb 2025 11:07:50 -0500 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
>>
>> The print_address_description() is run with a raw_spinlock_t acquired
>> and interrupt disabled. The find_vm_area() function 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. 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.
>>
> Thanks.  I added it and shall await review from the KASAN developers.
>
> I'm thinking we add
>
> Fixes: c056a364e954 ("kasan: print virtual mapping info in reports")
> Cc: <stable@vger.kernel.org>
>
> but c056a364e954 is 3 years old and I don't think we care about -rt in
> such old kernels.  Thoughts?

The KASAN report_lock was changed to a raw_spinlock_t in v6.13 kernel 
with commit e30a0361b851 ("kasan: make report_lock a raw spinlock") to 
fix a similar RT problem. The report_lock is acquired before calling 
print_address_description(). Before commit e30a0361b851, this 
find_vm_area() is a secondary issue. We may consider commit e30a0361b851 
isn't complete and this is a fix for that.

The DEFINE_WAIT_OVERRIDE_MAP() macro was introduced in v6.4. So this 
patch cannot be backported to a version earlier than that unless commit 
0cce06ba859a is there.

Cheers,
Longman