[PATCH] fixup bogus e820 entry with mem=

This was reported because someone was getting oopses reading /proc/iomem.
It was tracked down to a zero-sized 'struct resource' entry which was
located right at 4GB.

You need two conditions to hit this bug: a BIOS E820_RAM area starting at
exactly the boundary where you specify mem= (to get a zero-sized entry),
and for the legacy_init_iomem_resources() loop to skip that resource (which
only happens at exactly 4G).

I think the killing zero-sized e820 entry is the easiest way to fix this.
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/setup.c

@@ -389,14 +389,24 @@ static void __init limit_regions(unsigned long long size)
 		}
 	}
 	for (i = 0; i < e820.nr_map; i++) {
-		if (e820.map[i].type == E820_RAM) {
-			current_addr = e820.map[i].addr + e820.map[i].size;
-			if (current_addr >= size) {
-				e820.map[i].size -= current_addr-size;
-				e820.nr_map = i + 1;
-				return;
-			}
+		current_addr = e820.map[i].addr + e820.map[i].size;
+		if (current_addr < size)
+			continue;
+
+		if (e820.map[i].type != E820_RAM)
+			continue;
+
+		if (e820.map[i].addr >= size) {
+			/*
+			 * This region starts past the end of the
+			 * requested size, skip it completely.
+			 */
+			e820.nr_map = i;
+		} else {
+			e820.nr_map = i + 1;
+			e820.map[i].size -= current_addr - size;
 		}
+		return;
 	}
 }