md: set MD_CHANGE_PENDING in a atomic region

Some code waits for a metadata update by:

1. flagging that it is needed (MD_CHANGE_DEVS or MD_CHANGE_CLEAN)
2. setting MD_CHANGE_PENDING and waking the management thread
3. waiting for MD_CHANGE_PENDING to be cleared

If the first two are done without locking, the code in md_update_sb()
which checks if it needs to repeat might test if an update is needed
before step 1, then clear MD_CHANGE_PENDING after step 2, resulting
in the wait returning early.

So make sure all places that set MD_CHANGE_PENDING are atomicial, and
bit_clear_unless (suggested by Neil) is introduced for the purpose.

Cc: Martin Kepplinger <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: Sasha Levin <[email protected]>
Cc: <[email protected]>
Reviewed-by: NeilBrown <[email protected]>
Signed-off-by: Guoqing Jiang <[email protected]>
Signed-off-by: Shaohua Li <[email protected]>

0 files changed, 0 insertions, 0 deletions