Re: Kernel crash due to alloc_tag_top_users() being called when !mem_profiling_support?

[David Wang <00107082@163.com>]

> On Wed, Jun 18, 2025 at 02:25:37PM +0800, kernel test robot wrote:
> > 
> > Hello,
> > 
> > for this change, we reported
> > "[linux-next:master] [lib/test_vmalloc.c]  7fc85b92db: Mem-Info"
> > in
> > https://lore.kernel.org/all/202505071555.e757f1e0-lkp@intel.com/
> > 
> > at that time, we made some tests with x86_64 config which runs well.
> > 
> > now we noticed the commit is in mainline now.
> 
> (Re-sending due to not Ccing people and the list...)
> 
> Hi, I'm facing the same error on my testing environment.
> 
> I think this is related to memory allocation profiling & code tagging
> subsystems rather than vmalloc, so let's add related folks to Cc.
> 
> After a quick skimming of the code, it seems the condition
> to trigger this is that on 1) MEM_ALLOC_PROFILING is compiled but
> 2) not enabled by default. and 3) allocation somehow failed, calling
> alloc_tag_top_users().
> 
> I see "Memory allocation profiling is not supported!" in the dmesg,
> which means it did not alloc & inititialize alloc_tag_cttype properly,
> but alloc_tag_top_users() tries to acquire the semaphore.
> 
> I think the kernel should not call alloc_tag_top_users() at all (or it
> should return an error) if mem_profiling_support == false?
> 
> Does the following work on your testing environment?
> 
> (Only did very light testing on my QEMU, but seems to fix the issue for me.)
> 
> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> index d48b80f3f007..57d4d5673855 100644
> --- a/lib/alloc_tag.c
> +++ b/lib/alloc_tag.c
> @@ -134,7 +134,9 @@ size_t alloc_tag_top_users(struct codetag_bytes *tags, size_t count, bool can_sl
>  	struct codetag_bytes n;
>  	unsigned int i, nr = 0;
>  
> -	if (can_sleep)
> +	if (!mem_profiling_support)
> +		return 0;
> +	else if (can_sleep)
>  		codetag_lock_module_list(alloc_tag_cttype, true);
>  	else if (!codetag_trylock_module_list(alloc_tag_cttype))
>  		return 0;

I think you are correct, this was introduced/exposed by
commit 780138b1 ("alloc_tag: check mem_profiling_support in alloc_tag_init")
(Before the commit, the BUG would only be triggered when alloc_tag_init failed)


David