linux-kernel - [PATCH] mm/util.c: Make kvfree() safe for calling while holding spinlocks

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Message-Id: <20211222194828.15320-1-manfred@colorfullife.com>
Date:   Wed, 22 Dec 2021 20:48:28 +0100
From:   Manfred Spraul <manfred@...orfullife.com>
To:     LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Vasily Averin <vvs@...tuozzo.com>, cgel.zte@...il.com,
        shakeelb@...gle.com, rdunlap@...radead.org, dbueso@...e.de,
        unixbhaskar@...il.com, chi.minghao@....com.cn, arnd@...db.de,
        Zeal Robot <zealci@....com.cn>, linux-mm@...ck.org,
        1vier1@....de, Manfred Spraul <manfred@...orfullife.com>,
        stable@...r.kernel.org
Subject: [PATCH] mm/util.c: Make kvfree() safe for calling while holding spinlocks

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.

Reported-by: Zeal Robot <zealci@....com.cn>
Reported-by: Minghao Chi <chi.minghao@....com.cn>
Link: https://lore.kernel.org/all/20211222081026.484058-1-chi.minghao@zte.com.cn/
Fixes: fc37a3b8b438 ("[PATCH] ipc sem: use kvmalloc for sem_undo allocation")
Cc: stable@...r.kernel.org
Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
---
 mm/util.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 741ba32a43ac..7f9181998835 100644
--- 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);
 }
-- 
2.33.1