git: kernel -- ffs: Replace softupdates critical section locks with lockmgr.

[Venkatesh Srinivas]

commit 8e90f899fdf61479c5e76faa87e7ff716982ed08
Author: Venkatesh Srinivas <me at endeavour.zapto.org>
Date:   Wed Mar 28 11:09:15 2012 -0700

    kernel -- ffs: Replace softupdates critical section locks  with lockmgr.
    
    ffs softupdates was using a combination of critical sections and the mplock
    to construct its acquire_lock/free_lock/interlocked_sleep primitives.
    
    The softupdates I/O completion callback had a few points where it could block,
    causing it to lose the mplock and any critical sections it held. When it did
    so, front-end softupdates code would try to grab the lock but panic on seeing
    the I/O completion callback in progress. This was not a problem in older
    systems, as splx() would prevent the I/O callback from starting while
    softdep code was executing.
    
    This patch converts to using hard locks (lockmgr), which are held even while
    a thread is blocked.
    
    getdirtybuf(), locking a dirty buffer via BUF_LOCK, was changed to not
    deadlock against the I/O completion path; specifically it drops the softdep
    lock when its non-blocking attempt to lock a dirty buffer fails. One caller
    of getdirtybuf() also required changes to retry locking buffers.
    
    Closes-bug: 2291
    Partially-from: FreeBSD r140709
    Reported-by: tuxillo, marino, Rumko, vsrinivas
    Discussed-with: dillon

Summary of changes:
 sys/vfs/ufs/ffs_softdep.c |  356 +++++++++++++++------------------------------
 1 files changed, 117 insertions(+), 239 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/8e90f899fdf61479c5e76faa87e7ff716982ed08


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