tree 977805735b8ce122d67da721e8a960c15ef89769
parent 3d492c2e0146ccaad08c7cbe16e2e229328b5e79
author Tahsin Erdogan <tahsin@google.com> 1487129258 -0800
committer Jens Axboe <axboe@fb.com> 1487173204 -0700

block: do not allow updates through sysfs until registration completes

When a new disk shows up, sysfs queue directory is created before elevator
is registered. This allows a user to attempt a scheduler switch even though
the initial registration hasn't completed yet.

In one scenario, blk_register_queue() calls elv_register_queue() and
right before cfq_registered_queue() is called, another process executes
elevator_switch() and replaces q->elevator with deadline scheduler. When
cfq_registered_queue() executes it interprets e->elevator_data as struct
cfq_data even though it is actually struct deadline_data.

Grab q->sysfs_lock in blk_register_queue() to synchronize with sysfs
callers.

Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Signed-off-by: Jens Axboe <axboe@fb.com>