lkml.org 
[lkml]   [2019]   [Jul]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] mm: check for sleepable context in kvfree
On Tue, Jul 23, 2019 at 02:19:03PM -0400, Jeff Layton wrote:
> On Tue, 2019-07-23 at 11:11 -0700, Matthew Wilcox wrote:
> > On Tue, Jul 23, 2019 at 02:05:11PM -0400, Jeff Layton wrote:
> > > On Tue, 2019-07-23 at 10:55 -0700, Matthew Wilcox wrote:
> > > > I think it's a bit of a landmine, to be honest. How about we have kvfree()
> > > > call vfree_atomic() instead?
> > >
> > > Not a bad idea, though it means more overhead for the vfree case.
> > >
> > > Since we're spitballing here...could we have kvfree figure out whether
> > > it's running in a context where it would need to queue it instead and
> > > only do it in that case?
> > >
> > > We currently have to figure that out for the might_sleep_if anyway. We
> > > could just have it DTRT instead of printk'ing and dumping the stack in
> > > that case.
> >
> > I don't think we have a generic way to determine if we're currently
> > holding a spinlock. ie this can fail:
> >
> > spin_lock(&my_lock);
> > kvfree(p);
> > spin_unlock(&my_lock);
> >
> > If we're preemptible, we can check the preempt count, but !CONFIG_PREEMPT
> > doesn't record the number of spinlocks currently taken.
>
> Ahh right...that makes sense.
>
> Al also suggested on IRC that we could add a kvfree_atomic if that were
> useful. That might be good for new callers, but we'd probably need a
> patch like this one to suss out which of the existing kvfree callers
> would need to switch to using it.
>
> I think you're quite right that this is a landmine. That said, this
> seems like something we ought to try to clean up.

I'd rather add a kvfree_fast(). So something like this:

diff --git a/mm/util.c b/mm/util.c
index bab284d69c8c..992f0332dced 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -470,6 +470,28 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
}
EXPORT_SYMBOL(kvmalloc_node);

+/**
+ * kvfree_fast() - Free memory.
+ * @addr: Pointer to allocated memory.
+ *
+ * kvfree_fast frees memory allocated by any of vmalloc(), kmalloc() or
+ * kvmalloc(). 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. Must not
+ * hold a spinlock as it can sleep.
+ */
+void kvfree_fast(const void *addr)
+{
+ might_sleep();
+
+ if (is_vmalloc_addr(addr))
+ vfree(addr);
+ else
+ kfree(addr);
+}
+EXPORT_SYMBOL(kvfree_fast);
+
/**
* kvfree() - Free memory.
* @addr: Pointer to allocated memory.
@@ -478,12 +500,12 @@ 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.
*/
void kvfree(const void *addr)
{
if (is_vmalloc_addr(addr))
- vfree(addr);
+ vfree_atomic(addr);
else
kfree(addr);
}
\
 
 \ /
  Last update: 2019-07-23 20:30    [W:0.036 / U:1.256 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site