[md PATCH 00/18] Assorted minor fixes, particularly RCU protection.

NeilBrown
2016-06-02T06:19:52Z

The 'rdev' fields in each personality's config data are often accessed
under rcu_read_lock() protection to avoid races with
->hot_remove_disk() removing the rdev.

Originally this was not necessary during resync/recovery etc because
->hot_remove_disk() was only called from md_check_recovery(), and it
would only make the call if there was no resync etc happening.

However we now call ->hot_remove_disk() (from
remove_and_add_spares()) from other contexts, so there could be a race
in the resync code.

So this patch set adds a lot of extra rcu_read_lock protection and
clean up some other bits and pieces on the way.

My goal was the final patch. If you have a large raid10 array and
fail half of the devices at once (e.g. unplug a rack with half of the
mirrors) then synchronize_rcu() will be called once for each device,
which can add up to a big delay. A single call should suffice.
The final patch makes that change.

Thanks,
NeilBrown
---

NeilBrown (18):
md: disconnect device from personality before trying to remove it.
md/raid1,raid10: don't recheck "Faulty" flag in read-balance.
md/raid10: fix refounct imbalance when resyncing an array with a replacement device.
md/raid10: add rcu protection in raid10_status.
md/raid10: add rcu protection to rdev access in raid10_sync_request.
md/raid10: add rcu protection to rdev access during reshape.
md/raid10: minor code improvement in fix_read_error()
md/raid10: simplify print_conf a little.
md/raid10: stop print_conf from being too verbose.
md/raid1: small cleanup in raid1_end_read/write_request
md/raid1: small code cleanup in end_sync_write
md/raid1: add rcu protection to rdev in fix_read_error
md/raid5: add rcu protection to rdev accesses in handle_failed_sync.
md/raid5: add rcu protection to rdev accesses in want_replace
md/raid5: add rcu protection to rdev accesses in raid5_status.
md/multipath: add rcu protection to rdev access in multipath_status.
md: be extra careful not to take a reference to a Faulty device.
md: reduce the number of synchronize_rcu() calls when multiple devices fail.

drivers/md/md.c | 29 ++++++-
drivers/md/md.h | 5 +
drivers/md/multipath.c | 29 ++++---
drivers/md/raid1.c | 125 ++++++++++++++--------------
drivers/md/raid10.c | 213 +++++++++++++++++++++++++++++-------------------
drivers/md/raid5.c | 41 ++++++---
6 files changed, 264 insertions(+), 178 deletions(-)

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