Re: [linus:master] [mm] c6307674ed: BUG:sleeping_function_called_from_invalid_context_at_mm/vmalloc.c

[Uladzislau Rezki]

On Mon, Apr 27, 2026 at 10:53:52AM +0200, Vlastimil Babka wrote:
> On 4/23/26 05:34, Herbert Xu wrote:
> > On Wed, Apr 22, 2026 at 10:32:16AM +0200, Uladzislau Rezki wrote:
> >>
> >> We have added non-sleeping flags for vmalloc() to extend kvmalloc()
> >> functionality as folk need those.
> >>  
> >> Another option, would be: always use vfree_atomic() from the kvfree()
> >> path.
> >>  
> >> Any thoughts?
> > 
> > Perhaps add a kvfree_atomic that just calls vfree_atomic?
> 
> kvfree()'s comment says
> 
> " * Context: Either preemptible task context or not-NMI interrupt."
> 
I am not sure the description clearly reflects the intended usage.
To me it sounds like all contexts but excluding NMI.

For example, calling this under spin_lock() will be invalid, as
the vfree() path may invoke cond_resched().

> so this is neither. It might be ok then to create kvfree_atomic(). Always
> using vfree_atomic() from kvfree() might be wasteful.
> 
> > For rhashtable it really makes no difference either way.  But it
> > would eliminate the unsightly call to is_vmalloc_addr in rhashtable.
> > 
Seems atomic version makes sense here:

<snip>
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 15a60b501b95..2b5ab488e96b 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -1234,6 +1234,9 @@ void *kvrealloc_node_align_noprof(const void *p, size_t size, unsigned long alig
 extern void kvfree(const void *addr);
 DEFINE_FREE(kvfree, void *, if (!IS_ERR_OR_NULL(_T)) kvfree(_T))
 
+extern void kvfree_atomic(const void *addr);
+DEFINE_FREE(kvfree_atomic, void *, if (!IS_ERR_OR_NULL(_T)) kvfree_atomic(_T))
+
 extern void kvfree_sensitive(const void *addr, size_t len);
 
 unsigned int kmem_cache_size(struct kmem_cache *s);
diff --git a/mm/slub.c b/mm/slub.c
index 2b2d33cc735c..e25a0eab6ff7 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -6802,6 +6802,22 @@ void kvfree(const void *addr)
 }
 EXPORT_SYMBOL(kvfree);
 
+/**
+ * kvfree_atomic() - Free memory.
+ * @addr: Pointer to allocated memory.
+ *
+ * Same as kvfree(), but safe to use in atomic contexts.
+ * Must not be called from NMI context.
+ */
+void kvfree_atomic(const void *addr)
+{
+	if (is_vmalloc_addr(addr))
+		vfree_atomic(addr);
+	else
+		kfree(addr);
+}
+EXPORT_SYMBOL(kvfree_atomic);
+
 /**
  * kvfree_sensitive - Free a data object containing sensitive information.
  * @addr: address of the data object to be freed.
<snip>

I can post it if no objections.

--
Uladzislau Rezki