On 9/23/22 17:10, Uladzislau Rezki wrote:
On Fri, Sep 23, 2022 at 04:54:09PM +0200, Florian Westphal wrote:
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.
Doing the "p = kmalloc(sizeof(*p), GFP_ATOMIC);" from an atomic context
is also a problem nowadays. Such code should be fixed across the kernel
because of PREEMPT_RT support.
But the "atomic context" here is different, no? Calling kmalloc() from
IRQ handlers AFAIK is ok as IRQ handlers are threaded on PREEMPT_RT.
Calling it inside an local_irq_disable() would be a problem on the other
hand. But then under e.g. spin_lock_irqsave() could be ok as those don't
really disable irqs on RT.
--
Uladzislau Rezki
