Uladzislau Rezki <urezki@xxxxxxxxx> wrote:
> On Fri, Sep 23, 2022 at 03:35:12PM +0200, Florian Westphal wrote:
> > Michal Hocko <mhocko@xxxxxxxx> 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.
It uses kvzalloc, not vmalloc api.
Before 2018, rhashtable did use kzalloc OR kvzalloc, depending on gfp_t.
Quote from 93f976b5190df327939 changelog:
As of ce91f6ee5b3b ("mm: kvmalloc does not fallback to vmalloc for
incompatible gfp flags") we can simplify the caller
and trust kvzalloc() to just do the right thing.
I fear that if this isn't allowed it will result in hard-to-spot bugs
because things will work fine until a fallback to vmalloc happens.
rhashtable may not be the only user of kvmalloc api that rely on
ability to call it from (soft)irq.
