• David Howells's avatar
    [PATCH] keys: Discard key spinlock and use RCU for key payload · 76d8aeab
    David Howells authored
    The attached patch changes the key implementation in a number of ways:
    
     (1) It removes the spinlock from the key structure.
    
     (2) The key flags are now accessed using atomic bitops instead of
         write-locking the key spinlock and using C bitwise operators.
    
         The three instantiation flags are dealt with with the construction
         semaphore held during the request_key/instantiate/negate sequence, thus
         rendering the spinlock superfluous.
    
         The key flags are also now bit numbers not bit masks.
    
     (3) The key payload is now accessed using RCU. This permits the recursive
         keyring search algorithm to be simplified greatly since no locks need be
         taken other than the usual RCU preemption disablement. Searching now does
         not require any locks or semaphores to be held; merely that the starting
         keyring be pinned.
    
     (4) The keyring payload now includes an RCU head so that it can be disposed
         of by call_rcu(). This requires that the payload be copied on unlink to
         prevent introducing races in copy-down vs search-up.
    
     (5) The user key payload is now a structure with the data following it. It
         includes an RCU head like the keyring payload and for the same reason. It
         also contains a data length because the data length in the key may be
         changed on another CPU whilst an RCU protected read is in progress on the
         payload. This would then see the supposed RCU payload and the on-key data
         length getting out of sync.
    
         I'm tempted to drop the key's datalen entirely, except that it's used in
         conjunction with quota management and so is a little tricky to get rid
         of.
    
     (6) Update the keys documentation.
    Signed-Off-By: default avatarDavid Howells <dhowells@redhat.com>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    76d8aeab
request_key.c 9.07 KB