Re: commit 8031c3ddc70a breaks RAID5 on MIPS kernel where PAGE_SIZE == 64K

[Shaohua Li <shli@kernel.org>]

On Sun, Oct 08, 2017 at 04:34:52PM -0400, Joshua Kinard wrote:
> Hi,
> 
> Testing 4.13.5 out on my SGI Octane, I discovered that my RAID5 arrays were no
> longer auto-assembling.  The error being thrown was an "attempt to access
> beyond the end of the device".  I've hand-transcribed a block of these errors
> from a manual attempt to assemble the array via mdadm from a netboot image:
> 
> / # mdadm -A /dev/md0 /dev/sda1 /dev/sdb1 /dev/sdc1
> [   56.303339] md: md0 stopped.
> [   56.323565] md/raid:md0: device sda1 operational as raid disk 0
> [   56.334556] md/raid:md0: device sdb1 operational as raid disk 2
> [   56.345396] md/raid:md0: device sdc1 operational as raid disk 1
> [   56.350750] md/raid:md0: raid level 5 active with 3 out of 3 devices,
> algorithm 2
> [   56.369529] attempt to access beyond end of device
> [   56.380149] sda1: rw=2048, want=4194312, limit=4194305
> [   56.390823] attempt to access beyond end of device
> [   56.401500] sdc1: rw=2048, want=4194312, limit=4194305
> [   56.412313] attempt to access beyond end of device
> [   56.423146] sdb1: rw=2048, want=4194312, limit=4194305
> [   56.433985] md0: failed to create bitmap (-5)
> mdadm: failed to RUN_ARRAY /dev/md0: input/output error
> [   56.457979] md: md0 stopped.
> / #
> 
> I've traced the offending commit down to 8031c3ddc70a ("md/bitmap: copy correct
> data for bitmap super"):
> 
> https://git.linux-mips.org/cgit/ralf/linux.git/commit/?id=8031c3ddc70ab93099e7d1814382dba39f57b43e
> 
> Per the commit message, it makes an assumption that PAGE_SIZE is 4K.  MIPS
> kernels allow you to change the value of PAGE_SIZE at compile time to something
> other than 4K.  It appears that 4K and 16K both work, while 64K, which is what
> I use on this machine, is broken with this commit applied.
> 
> Reverting this patch or setting PAGE_SIZE to 4K or 16K will resolve the issue,
> but there are advantages to using 64K PAGE_SIZEs on these platforms.  I am not
> sure that 16K is wholly safe either, FWIW, given the assumption made in the commit.

Can you try below one?


diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index d2121637b4ab..f68ec973fbdd 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -153,6 +153,7 @@ static int read_sb_page(struct mddev *mddev, loff_t offset,
 
 	struct md_rdev *rdev;
 	sector_t target;
+	int target_size;
 
 	rdev_for_each(rdev, mddev) {
 		if (! test_bit(In_sync, &rdev->flags)
@@ -161,9 +162,12 @@ static int read_sb_page(struct mddev *mddev, loff_t offset,
 			continue;
 
 		target = offset + index * (PAGE_SIZE/512);
+		target_size = min_t(u64, size, i_size_read(rdev->bdev->bd_inode) -
+			((target + rdev->sb_start) << 9));
+		target_size = roundup(target_size,
+			bdev_logical_block_size(rdev->bdev));
 
-		if (sync_page_io(rdev, target,
-				 roundup(size, bdev_logical_block_size(rdev->bdev)),
+		if (sync_page_io(rdev, target, target_size,
 				 page, REQ_OP_READ, 0, true)) {
 			page->index = index;
 			return 0;