linux-kernel - [PATCH] mm: Make kvfree safe to call

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Date:   Fri, 26 Jul 2019 14:01:37 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Jeff Layton <jlayton@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Luis Henriques <lhenriques@...e.com>,
        Christoph Hellwig <hch@....de>,
        Carlos Maiolino <cmaiolino@...hat.com>
Subject: [PATCH] mm: Make kvfree safe to call

From: "Matthew Wilcox (Oracle)" <willy@...radead.org>

Since vfree() can sleep, calling kvfree() from contexts where sleeping
is not permitted (eg holding a spinlock) is a bit of a lottery whether
it'll work.  Introduce kvfree_safe() for situations where we know we can
sleep, but make kvfree() safe by default.

Reported-by: Jeff Layton <jlayton@...nel.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Luis Henriques <lhenriques@...e.com>
Cc: Christoph Hellwig <hch@....de>
Cc: Carlos Maiolino <cmaiolino@...hat.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
 mm/util.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

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);
 }
-- 
2.20.1