Re: initrd support broken in mips kernel 4.2

[Alexander Sverdlin <alexander.sverdlin@gmail.com>]

Hello Tony,

On 02/09/15 23:25, Alexander Sverdlin wrote:
>> Commit a6335fa11 (MIPS: bootmem: Don't use memory holes for page bitmap) 
>> > crashes kernel with a initramfs unpacking error when initrd is enabled. 
>> > 
>> > ---- error message ----
>> > Unpacking initramfs...
>> > Initramfs unpacking failed: junk in compressed archive
>> > BUG: Bad page state in process swapper  pfn:00261
>> > page:81004c20 count:0 mapcount:-127 mapping:  (null) index:0x2
>> > flags: 0x0()
>> > page dumped because: nonzero mapcount
>> > CPU: 0 PID: 1 Comm: swapper Not tainted 4.2.0+ #1782
>> > -----------------------
>> > 
>> > The modified logic in bootmem_init does not guarantee mapstart to be placed 
>> > after initrd_end. mapstart is set to the maximum of reserved_end and
>> > start. In case initrd_end is greater than reserved_end, mapstart is placed
>> > before initrd_end, and causes initramfs unpacking error.
> Indeed, seems that there are two problems with the patch. First, "<=" is wrong
> in the condition. This will fail if initrd and next zone are separated (in
> boot_mem_map), but have not gap in between. Second, without gap, initrd and PFN

Oh, "<=" is indeed correct. Could you please test this patch instead of the
previously proposed:

--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -338,7 +338,7 @@ static void __init bootmem_init(void)
 		if (end <= reserved_end)
 			continue;
 #ifdef CONFIG_BLK_DEV_INITRD
-		/* mapstart should be after initrd_end */
+		/* Skip zones before initrd and initrd itself */
 		if (initrd_end && end <= (unsigned long)PFN_UP(__pa(initrd_end)))
 			continue;
 #endif
@@ -371,6 +371,14 @@ static void __init bootmem_init(void)
 		max_low_pfn = PFN_DOWN(HIGHMEM_START);
 	}

+#ifdef CONFIG_BLK_DEV_INITRD
+	/*
+	 * mapstart should be after initrd_end
+	 */
+	if (initrd_end)
+		mapstart = max(mapstart, (unsigned long)PFN_UP(__pa(initrd_end)));
+#endif
+
 	/*
 	 * Initialize the boot-time allocator with low memory only.
 	 */