Re: [PATCH mm] mm: fix BUG with kvzalloc+GFP_ATOMIC

[Uladzislau Rezki <urezki@gmail.com>]

On Fri, Sep 23, 2022 at 03:35:12PM +0200, Florian Westphal wrote:
> Michal Hocko <mhocko@suse.com> wrote:
> > On Fri 23-09-22 12:38:58, Florian Westphal wrote:
> > > Martin Zaharinov reports BUG() in mm land for 5.19.10 kernel:
> > >  kernel BUG at mm/vmalloc.c:2437!
> > >  invalid opcode: 0000 [#1] SMP
> > >  CPU: 28 PID: 0 Comm: swapper/28 Tainted: G        W  O      5.19.9 #1
> > >  [..]
> > >  RIP: 0010:__get_vm_area_node+0x120/0x130
> > >   __vmalloc_node_range+0x96/0x1e0
> > >   kvmalloc_node+0x92/0xb0
> > >   bucket_table_alloc.isra.0+0x47/0x140
> > >   rhashtable_try_insert+0x3a4/0x440
> > >   rhashtable_insert_slow+0x1b/0x30
> > >  [..]
> > > 
> > > bucket_table_alloc uses kvzallocGPF_ATOMIC).  If kmalloc fails, this now
> > > falls through to vmalloc and hits code paths that assume GFP_KERNEL.
> > > 
> > > Revert the problematic change and stay with slab allocator.
> > 
> > Why don't you simply fix the caller?
> 
> Uh, not following?
> 
> kvzalloc(GFP_ATOMIC) was perfectly fine, is this illegal again?
>
<snip>
static struct vm_struct *__get_vm_area_node(unsigned long size,
		unsigned long align, unsigned long shift, unsigned long flags,
		unsigned long start, unsigned long end, int node,
		gfp_t gfp_mask, const void *caller)
{
	struct vmap_area *va;
	struct vm_struct *area;
	unsigned long requested_size = size;

	BUG_ON(in_interrupt());
...
<snip>

vmalloc is not supposed to be called from the IRQ context. If it is possible
it would be better to fix the bucket_table_alloc() by not calling it from the
IRQ context.  

--
Uladzislau Rezki