On Thu 27-01-22 06:59:50, Manfred Spraul wrote: > Hi Andrew, > > On 1/27/22 03:53, Andrew Morton wrote: > > On Wed, 22 Dec 2021 20:48:28 +0100 Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> wrote: > > > > > One codepath in find_alloc_undo() calls kvfree() while holding a spinlock. > > > Since vfree() can sleep this is a bug. > > > > > > Previously, the code path used kfree(), and kfree() is safe to be called > > > while holding a spinlock. > > > > > > Minghao proposed to fix this by updating find_alloc_undo(). > > > > > > Alternate proposal to fix this: Instead of changing find_alloc_undo(), > > > change kvfree() so that the same rules as for kfree() apply: > > > Having different rules for kfree() and kvfree() just asks for bugs. > > > > > > Disadvantage: Releasing vmalloc'ed memory will be delayed a bit. > > I know we've been around this loop a bunch of times and deferring was > > considered. But I forget the conclusion. IIRC, mhocko was involved? > > I do not remember a mail from mhocko. I do not remember either. > > Shakeel proposed to use the approach from Chi. > > Decision: https://marc.info/?l=linux-kernel&m=164132032717757&w=2 And I would agree with Shakeel and go with the original change to the ipc code. That is trivial and without any other side effects like this one. I bet nobody has evaluated what the undconditional deferred freeing has. At least changelog doesn't really dive into that more than a very vague statement that this will happen. > With Reviewed-by: > > https://marc.info/?l=linux-kernel&m=164132744522325&w=2 > > > --- a/mm/util.c > > > +++ b/mm/util.c > > > @@ -610,12 +610,12 @@ EXPORT_SYMBOL(kvmalloc_node); > > > * It is slightly more efficient to use kfree() or vfree() if you are certain > > > * that you know which one to use. > > > * > > > - * Context: Either preemptible task context or not-NMI interrupt. > > > + * Context: Any context except NMI interrupt. > > > */ > > > void kvfree(const void *addr) > > > { > > > if (is_vmalloc_addr(addr)) > > > - vfree(addr); > > > + vfree_atomic(addr); > > > else > > > kfree(addr); > > > } > -- Michal Hocko SUSE Labs
