Patch "fs, seqfile: always allow oom killer" has been added to the 4.3-stable tree

This is a note to let you know that I've just added the patch titled

fs, seqfile: always allow oom killer

to the 4.3-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
fs-seqfile-always-allow-oom-killer.patch
and it can be found in the queue-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Greg Thelen <[email protected]>
Date: Fri, 6 Nov 2015 16:32:42 -0800
Subject: fs, seqfile: always allow oom killer

From: Greg Thelen <[email protected]>

commit 0f930902eb8806cff8dcaef9ff9faf3cfa5fd748 upstream.

Since 5cec38ac866b ("fs, seq_file: fallback to vmalloc instead of oom kill processes") seq_buf_alloc() avoids calling the oom killer for PAGE_SIZE or smaller allocations; but larger allocations can use the oom killer via vmalloc(). Thus reads of small files can return ENOMEM, but larger files use the oom killer to avoid ENOMEM.

The effect of this bug is that reads from /proc and other virtual filesystems can return ENOMEM instead of the preferred behavior - oom killing something (possibly the calling process). I don't know of anyone except Google who has noticed the issue.

I suspect the fix is more needed in smaller systems where there isn't any reclaimable memory. But these seem like the kinds of systems which probably don't use the oom killer for production situations.

Memory overcommit requires use of the oom killer to select a victim regardless of file size.

Enable oom killer for small seq_buf_alloc() allocations.

---
 fs/seq_file.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

@@ -25,12 +25,17 @@ static void seq_set_overflow(struct seq_
 static void *seq_buf_alloc(unsigned long size)
 {
 	void *buf;
+	gfp_t gfp = GFP_KERNEL;
 
 	/*
-	 * __GFP_NORETRY to avoid oom-killings with high-order allocations -
-	 * it's better to fall back to vmalloc() than to kill things.
+	 * For high order allocations, use __GFP_NORETRY to avoid oom-killing -
+	 * it's better to fall back to vmalloc() than to kill things.  For small
+	 * allocations, just use GFP_KERNEL which will oom kill, thus no need
+	 * for vmalloc fallback.
 	 */
-	buf = kmalloc(size, GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN);
+	if (size > PAGE_SIZE)
+		gfp |= __GFP_NORETRY | __GFP_NOWARN;
+	buf = kmalloc(size, gfp);
 	if (!buf && size > PAGE_SIZE)
 		buf = vmalloc(size);
 	return buf;

Patches currently in stable-queue which might be from [email protected] are

queue-4.3/fs-seqfile-always-allow-oom-killer.patch