I was looking at the code for register_blkdev and unregister_blkdev. I 
found that no
locking (spinlocks) are used to protect the blkdevs struture in these 
functions. I suspect
we have not seen a problem till now since

Either

1. register_blkdev is called from modules, and only module 
initialization is protected.
2. register_blkdev is called during init time for drivers in the kernel 
and I am not sure
    about whether calls to register_blkdev at this time are implicitly 
serialized, since only
    1 CPU is active during initialization

Anway, what I needed to know was if (1) and (2) are enough to ensure 
safety in register_blkdev
and unregister_blkdev.

May be I am missing something, there is already some lock which is held 
before these routines
are invoked, I could not find any.

Comments

Thanks,
Balbir Singh.