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

Commit bdee237c ("x86: mm: Use 2GB memory block size on large-memory
x86-64 systems") and 982792c7 ("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=107781Signed-off-by: NSeth Jennings <sjennings@variantweb.net>
Reported-by: NAndrew Banman <abanman@sgi.com>
Cc: Daniel J Blueman <daniel@numascale.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Greg KH <greg@kroah.com>
Cc: Russ Anderson <rja@sgi.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

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);
 }