md: Relax minimum size restrictions on chunk_size.

Currently, the 'chunk_size' of an array must be at-least PAGE_SIZE.

This makes moving an array to a machine with a larger PAGE_SIZE, or
changing the kernel to use a larger PAGE_SIZE, can stop an array from
working.

For RAID10 and RAID4/5/6, this is non-trivial to fix as the resync
process works on whole pages at a time, and assumes them to be wholly
within a stripe.  For other raid personalities, this restriction is
not needed at all and can be dropped.

So remove the test on chunk_size from common can, and add it in just
the places where it is needed: raid10 and raid4/5/6.

Signed-off-by: NeilBrown <neilb@suse.de>

3 files changed, 11 insertions, 8 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index a29187d1fcf5..be2014f6e37b 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -3520,17 +3520,12 @@ static int do_md_run(mddev_t * mddev)
                         return -EINVAL;
                 }
                 /*
-                 * chunk-size has to be a power of 2 and multiples of PAGE_SIZE
+                 * chunk-size has to be a power of 2
                  */
                 if ( (1 << ffz(~chunk_size)) != chunk_size) {
                         printk(KERN_ERR "chunk_size of %d not valid\n", chunk_size);
                         return -EINVAL;
                 }
-                if (chunk_size < PAGE_SIZE) {
-                        printk(KERN_ERR "too small chunk_size: %d < %ld\n",
-                                chunk_size, PAGE_SIZE);
-                        return -EINVAL;
-                }
 
                 /* devices must have minimum size of one chunk */
                 rdev_for_each(rdev, tmp, mddev) {
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 8bdc9bfc2887..e3794799f308 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2028,8 +2028,9 @@ static int run(mddev_t *mddev)
         int nc, fc, fo;
         sector_t stride, size;
 
-        if (mddev->chunk_size == 0) {
-                printk(KERN_ERR "md/raid10: non-zero chunk size required.\n");
+        if (mddev->chunk_size < PAGE_SIZE) {
+                printk(KERN_ERR "md/raid10: chunk size must be "
+                       "at least PAGE_SIZE(%ld).\n", PAGE_SIZE);
                 return -EINVAL;
         }
 
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index d72be4b89e64..a36a7435edf5 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4007,6 +4007,13 @@ static int run(mddev_t *mddev)
                 return -EIO;
         }
 
+        if (mddev->chunk_size < PAGE_SIZE) {
+                printk(KERN_ERR "md/raid5: chunk_size must be at least "
+                       "PAGE_SIZE but %d < %ld\n",
+                       mddev->chunk_size, PAGE_SIZE);
+                return -EINVAL;
+        }
+
         if (mddev->reshape_position != MaxSector) {
                 /* Check that we can continue the reshape.
                  * Currently only disks can change, it must