On Wed, 10 Jul 2013 19:54:09 +0200 Martin Wilck <mwilck@xxxxxxxx> wrote: > Hi Neil, hi all, > > I discovered a weird behavior of mdadm -Db - it will switch a RAID array > from read-auto state to write-pending. For DDF (and possibly other > formats) this will cause metadata writes. > > If I read the code correctly, the reason is that mdadm -Db will use the > GET_BITMAP_FILE ioctl, which calls md_allow_write(). I saw this on a > CentOS 6.3 kernel but comparing the code I didn't see a difference in > recent kernels. > > I am wondering if this is intentional, and if no, if anything could be > done about it. It is certainly surprising behavior. > > Regards > Martin I hadn't thought of that consequence. Probably the best thing to do is: diff --git a/drivers/md/md.c b/drivers/md/md.c index d059af5..b19a1c8 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -5629,10 +5629,7 @@ static int get_bitmap_file(struct mddev * mddev, void __user * arg) char *ptr, *buf = NULL; int err = -ENOMEM; - if (md_allow_write(mddev)) - file = kmalloc(sizeof(*file), GFP_NOIO); - else - file = kmalloc(sizeof(*file), GFP_KERNEL); + file = kmalloc(sizeof(*file), GFP_NOIO); if (!file) goto out; A failure here is not likely and not catastrophic. Does it fix the situation for you? NeilBrown
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