[4.2.y-ckt stable] Patch "drivers/base/memory.c: prohibit offlining of memory blocks with missing sections" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    drivers/base/memory.c: prohibit offlining of memory blocks with missing sections

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 9e44f16905d9210070f7d6595040a88b925c9911 Mon Sep 17 00:00:00 2001
From: Seth Jennings <sjennings at variantweb.net>
Date: Fri, 11 Dec 2015 13:40:57 -0800
Subject: drivers/base/memory.c: prohibit offlining of memory blocks with
 missing sections

commit 26bbe7ef6d5cdc7ec08cba6d433fca4060f258f3 upstream.

Commit bdee237c0343 ("x86: mm: Use 2GB memory block size on large-memory
x86-64 systems") and 982792c782ef ("x86, mm: probe memory block size for
generic x86 64bit") introduced large block sizes for x86.  This made it
possible to have multiple sections per memory block where previously,
there was a only every one section per block.

Since blocks consist of contiguous ranges of section, there can be holes
in the blocks where sections are not present.  If one attempts to
offline such a block, a crash occurs since the code is not designed to
deal with this.

This patch is a quick fix to gaurd against the crash by not allowing
blocks with non-present sections to be offlined.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=107781

Signed-off-by: Seth Jennings <sjennings at variantweb.net>
Reported-by: Andrew Banman <abanman at sgi.com>
Cc: Daniel J Blueman <daniel at numascale.com>
Cc: Yinghai Lu <yinghai at kernel.org>
Cc: Greg KH <greg at kroah.com>
Cc: Russ Anderson <rja at sgi.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/base/memory.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 2804aed..25425d3 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -303,6 +303,10 @@ static int memory_subsys_offline(struct device *dev)
 	if (mem->state == MEM_OFFLINE)
 		return 0;

+	/* Can't offline block with non-present sections */
+	if (mem->section_count != sections_per_block)
+		return -EINVAL;
+
 	return memory_block_change_state(mem, MEM_OFFLINE, MEM_ONLINE);
 }

--
1.9.1