Re: [PATCH v3] kasan: Don't call find_vm_area() in RT kernel

[Waiman Long <llong@redhat.com>]

On 2/17/25 11:28 AM, Andrey Konovalov wrote:
> On Mon, Feb 17, 2025 at 5:21 AM 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.
>>
>> Fixes: e30a0361b851 ("kasan: make report_lock a raw spinlock")
>> Signed-off-by: Waiman Long <longman@redhat.com>
>> ---
>>   mm/kasan/report.c | 43 ++++++++++++++++++++++++++++++-------------
>>   1 file changed, 30 insertions(+), 13 deletions(-)
>>
>>   [v3] Rename helper to print_vmalloc_info_set_page.
>>
>> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
>> index 3fe77a360f1c..7c8c2e173aa4 100644
>> --- a/mm/kasan/report.c
>> +++ b/mm/kasan/report.c
>> @@ -370,6 +370,34 @@ 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.
> Quoting your response from the other thread:
>
>> Lockdep currently issues warnings for taking spinlock_t inside
>> raw_spinlock_t because it is not allowed in RT. Test coverage of RT
>> kernels is likely less than !RT kernel and so less bug of this kind will
>> be caught. By making !RT doing the same check, we increase coverage.
>> However, we do allow override in the !RT case, but it has to be done on
>> a case-by-case basis.
> Got it.
>
> So let's put this exactly this explanation in the comment, otherwise
> it's unclear why we need something special for the !RT case.

Sure. Will do that.


>> + */
>> +static inline void print_vmalloc_info_set_page(void *addr, struct page **ppage)
>> +{
>> +       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);
>> +               if (va) {
>> +                       pr_err("The buggy address belongs to the virtual mapping at\n"
>> +                              " [%px, %px) created by:\n"
>> +                              " %pS\n",
>> +                              va->addr, va->addr + va->size, va->caller);
>> +                       pr_err("\n");
>> +
>> +                       *ppage = vmalloc_to_page(addr);
> Looking at the code again, I actually like the Andrey Ryabinin's
> suggestion from the v1 thread: add a separate function that contains
> an annotated call of find_vm_area(). And keep vmalloc_to_page()
> outside of it, just as done in the upstream version now.

I can make the change if it is what you want.

Cheers,
Longman