On 05/15/2018 12:49 AM, Shaohua Li wrote:
On Fri, May 11, 2018 at 10:46:59AM +0800, Xiao Ni wrote:
Hi Shaohua
On 05/11/2018 06:23 AM, Shaohua Li wrote:
From: Shaohua Li <shli@xxxxxx>
The recent flush request handling seems unncessary complicated. The main
issue is in rdev_end_flush we can either get rdev of the bio or the
flush_info, not both, or we need extra memory to for the other. With the
extra memory, we need reallocate the memory in disk hotadd/remove.
Actually the original patch forgets one case of add_new_disk for memory
allocation, and we have kernel crash.
add_new_disk just adds disk to md as a spare disk. After reshape raid
disks update_raid_disks realloc memory. Why is there a kernel crash?
Could you explain more?
Not always reshape. It's very easy to reproduce. Just create a linear array,
grow up one disk, and run some file io triggering flush.
Hi Shaohua
How do I grow up one disk after creating a raid0 array? Something like
those steps?
mdadm -CR /dev/md0 -l1 -n2 /dev/sdb1 /dev/sdc1 --size=50M
mdadm -CR /dev/md1 -l0 /dev/md0 /dev/sdd2
mdadm /dev/md0 --grow --size=max
I read the code again and I still can't catch the point. In
md_flush_request it just sends
flush bio to md_rdev which is not faulty and the raid_disk is not -1.
After add_new_disk
the md_rdev->raid_disk is -1. It can change to the role number only
after reshaping. So
for this situation it can't panic.
The idea is always to increase all rdev reference in md_flush_request
and decrease the references after bio finish. In this way,
rdev_end_flush doesn't need to know rdev, so we don't need to allocate
extra memory.
Is there a situation like this? It plugs one disk to the raid after the
flush
bios submitted to underlayer disks. After those flush bios come back there
is one more rdev in the list mddev->disks. If decrements all rdev reference
at one time, it can decrease the rdev reference which doesn't submit flush
bio. It's the reason I try to allocate memory for bios[0] in flush_info.
I think we wait all IO finish before the hot add/remove disks.
I read the related codes and did some tests. In fact it don't wait IO
finish. I call raid1 get_unqueued_pending
in add_new_disk before bind_rdev_to_array(list_add_rcu(&rdev->same_set,
&mddev->disks); ). it shows
there are I/O. Should it call mddev_suspend in add_new_disk? If it can
wait all IO finish, there is no need to
alloc memory for bios[]
Regards
Xiao
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