• NeilBrown's avatar
    sched: Remove proliferation of wait_on_bit() action functions · 74316201
    NeilBrown authored
    The current "wait_on_bit" interface requires an 'action'
    function to be provided which does the actual waiting.
    There are over 20 such functions, many of them identical.
    Most cases can be satisfied by one of just two functions, one
    which uses io_schedule() and one which just uses schedule().
    
    So:
     Rename wait_on_bit and        wait_on_bit_lock to
            wait_on_bit_action and wait_on_bit_lock_action
     to make it explicit that they need an action function.
    
     Introduce new wait_on_bit{,_lock} and wait_on_bit{,_lock}_io
     which are *not* given an action function but implicitly use
     a standard one.
     The decision to error-out if a signal is pending is now made
     based on the 'mode' argument rather than being encoded in the action
     function.
    
     All instances of the old wait_on_bit and wait_on_bit_lock which
     can use the new version have been changed accordingly and their
     action functions have been discarded.
     wait_on_bit{_lock} does not return any specific error code in the
     event of a signal so the caller must check for non-zero and
     interpolate their own error code as appropriate.
    
    The wait_on_bit() call in __fscache_wait_on_invalidate() was
    ambiguous as it specified TASK_UNINTERRUPTIBLE but used
    fscache_wait_bit_interruptible as an action function.
    David Howells confirms this should be uniformly
    "uninterruptible"
    
    The main remaining user of wait_on_bit{,_lock}_action is NFS
    which needs to use a freezer-aware schedule() call.
    
    A comment in fs/gfs2/glock.c notes that having multiple 'action'
    functions is useful as they display differently in the 'wchan'
    field of 'ps'. (and /proc/$PID/wchan).
    As the new bit_wait{,_io} functions are tagged "__sched", they
    will not show up at all, but something higher in the stack.  So
    the distinction will still be visible, only with different
    function names (gds2_glock_wait versus gfs2_glock_dq_wait in the
    gfs2/glock.c case).
    
    Since first version of this patch (against 3.15) two new action
    functions appeared, on in NFS and one in CIFS.  CIFS also now
    uses an action function that makes the same freezer aware
    schedule call as NFS.
    Signed-off-by: default avatarNeilBrown <neilb@suse.de>
    Acked-by: David Howells <dhowells@redhat.com> (fscache, keys)
    Acked-by: Steven Whitehouse <swhiteho@redhat.com> (gfs2)
    Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Steve French <sfrench@samba.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Link: http://lkml.kernel.org/r/20140707051603.28027.72349.stgit@notabene.brownSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    74316201
transaction.c 74.9 KB