>
> On Thu, Aug 17, 2023 at 2:34 AM Zqiang <qiang.zhang1211@xxxxxxxxx> wrote:
> >
> > Currently, for double invoke call_rcu(), will dump rcu_head objects
> > memory info, if the objects is not allocated from the slab allocator,
> > the vmalloc_dump_obj() will be invoke and the vmap_area_lock spinlock
> > need to be held, since the call_rcu() can be invoked in interrupt context,
> > therefore, there is a possibility of spinlock deadlock scenarios.
> >
> > And in Preempt-RT kernel, the rcutorture test also trigger the following
> > lockdep warning:
> >
> > BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
> > in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 1, name: swapper/0
> [...]
> >
> > The statistics about the source of 'rhp', the kmem_valid_obj() accounts
> > for more than 97.5%, and vmalloc accounts for less than 1%, this statistic
> > comes from leizhen. this commit therefore drop vmalloc_dump_obj() from
> > mem_dump_obj() and only check whether is vmalloc address.
> > Signed-off-by: Zqiang <qiang.zhang1211@xxxxxxxxx>
> > ---
> > include/linux/vmalloc.h | 5 -----
> > mm/util.c | 7 +++----
> > mm/vmalloc.c | 14 --------------
> > 3 files changed, 3 insertions(+), 23 deletions(-)
> >
> > diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> > index c720be70c8dd..d7c4e112a4ad 100644
> > --- a/include/linux/vmalloc.h
> > +++ b/include/linux/vmalloc.h
> > @@ -289,10 +289,5 @@ pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
> > int register_vmap_purge_notifier(struct notifier_block *nb);
> > int unregister_vmap_purge_notifier(struct notifier_block *nb);
> >
> > -#if defined(CONFIG_MMU) && defined(CONFIG_PRINTK)
> > -bool vmalloc_dump_obj(void *object);
> > -#else
> > -static inline bool vmalloc_dump_obj(void *object) { return false; }
> > -#endif
> >
> > #endif /* _LINUX_VMALLOC_H */
> > diff --git a/mm/util.c b/mm/util.c
> > index ddfbb22dc187..fbc007adc108 100644
> > --- a/mm/util.c
> > +++ b/mm/util.c
> > @@ -1066,10 +1066,9 @@ void mem_dump_obj(void *object)
> > if (kmem_dump_obj(object))
> > return;
> >
> > - if (vmalloc_dump_obj(object))
> > - return;
> > -
> > - if (virt_addr_valid(object))
> > + if (is_vmalloc_addr(object))
> > + type = "vmalloc memory";
> > + else if (virt_addr_valid(object))
> > type = "non-slab/vmalloc memory";
> > else if (object == NULL)
> > type = "NULL pointer";
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 93cf99aba335..224af955bcb5 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -4271,20 +4271,6 @@ void pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
> > }
> > #endif /* CONFIG_SMP */
> >
> > -#ifdef CONFIG_PRINTK
> > -bool vmalloc_dump_obj(void *object)
> > -{
> > - struct vm_struct *vm;
> > - void *objp = (void *)PAGE_ALIGN((unsigned long)object);
> > -
> > - vm = find_vm_area(objp);
>
> What about adding something like the following to vmalloc.c. Would it work?
>
> +static struct vmap_area *find_vmap_area_trylock(unsigned long addr)
> +{
> + struct vmap_area *va;
> +
> + if (!spin_trylock(&vmap_area_lock))
> + return NULL;
> + va = __find_vmap_area(addr);
> + spin_unlock(&vmap_area_lock);
> +
> + return va;
> +}
>
> and call it from vmalloc_dump_obj():
>
> vm = find_vm_area_trylock(objp);
>
> And then keep the rest of your patch as it is but add back the call to
> vmalloc_dump_obj() in mem_dump_obj():
>
> if (vmalloc_dump_obj(object))
> return;
>
> - if (virt_addr_valid(object))
> + if (is_vmalloc_addr(object))
> + type = "vmalloc memory";
> + else if (virt_addr_valid(object))
> type = "non-slab/vmalloc memory";
>
>
> If that still throws "sleeping function called" type warnings, then
> that is a preempt RT issue because spin_trylock() on conversion to a
> sleeping lock should not be sleeping as it is uncontended.
>
Hello, Joel
I did a test in the RT kernel with the following modifications, and
didn't trigger
sleeping function called warning.
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 93cf99aba335..e07b0e34249b 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4272,12 +4272,24 @@ void pcpu_free_vm_areas(struct vm_struct
**vms, int nr_vms)
#endif /* CONFIG_SMP */
#ifdef CONFIG_PRINTK
+static struct vm_struct *find_vmap_area_trylock(unsigned long addr)
+{
+ struct vmap_area *va;
+
+ if (!spin_trylock(&vmap_area_lock))
+ return NULL;
+ va = __find_vmap_area(addr, &vmap_area_root);
+ spin_unlock(&vmap_area_lock);
+
+ return va ? va->vm : NULL;
+}
+
bool vmalloc_dump_obj(void *object)
{
struct vm_struct *vm;
void *objp = (void *)PAGE_ALIGN((unsigned long)object);
- vm = find_vm_area(objp);
+ vm = find_vmap_area_trylock((unsigned long)objp);
if (!vm)
return false;
pr_cont(" %u-page vmalloc region starting at %#lx allocated at %pS\n",
If double call_rcu() appears in different threads at the same time,
It is possible to dump only one of the vmalloc information.
Thanks
Zqiang
>
> But I could be missing something and I'll look more later. But for now
> off to pick up a rental car here...
>
> thanks,
>
> - Joel
