1. 14 Sep, 2009 1 commit
    • Frederic Weisbecker's avatar
      reiserfs: kill-the-BKL · 8ebc4232
      Frederic Weisbecker authored
      This patch is an attempt to remove the Bkl based locking scheme from
      reiserfs and is intended.
      
      It is a bit inspired from an old attempt by Peter Zijlstra:
      
         http://lkml.indiana.edu/hypermail/linux/kernel/0704.2/2174.html
      
      The bkl is heavily used in this filesystem to prevent from
      concurrent write accesses on the filesystem.
      
      Reiserfs makes a deep use of the specific properties of the Bkl:
      
      - It can be acqquired recursively by a same task
      - It is released on the schedule() calls and reacquired when schedule() returns
      
      The two properties above are a roadmap for the reiserfs write locking so it's
      very hard to simply replace it with a common mutex.
      
      - We need a recursive-able locking unless we want to restructure several blocks
        of the code.
      - We need to identify the sites where the bkl was implictly relaxed
        (schedule, wait, sync, etc...) so that we can in turn release and
        reacquire our new lock explicitly.
        Such implicit releases of the lock are often required to let other
        resources producer/consumer do their job or we can suffer unexpected
        starvations or deadlocks.
      
      So the new lock that replaces the bkl here is a per superblock mutex with a
      specific property: it can be acquired recursively by a same task, like the
      bkl.
      
      For such purpose, we integrate a lock owner and a lock depth field on the
      superblock information structure.
      
      The first axis on this patch is to turn reiserfs_write_(un)lock() function
      into a wrapper to manage this mutex. Also some explicit calls to
      lock_kernel() have been converted to reiserfs_write_lock() helpers.
      
      The second axis is to find the important blocking sites (schedule...(),
      wait_on_buffer(), sync_dirty_buffer(), etc...) and then apply an explicit
      release of the write lock on these locations before blocking. Then we can
      safely wait for those who can give us resources or those who need some.
      Typically this is a fight between the current writer, the reiserfs workqueue
      (aka the async commiter) and the pdflush threads.
      
      The third axis is a consequence of the second. The write lock is usually
      on top of a lock dependency chain which can include the journal lock, the
      flush lock or the commit lock. So it's dangerous to release and trying to
      reacquire the write lock while we still hold other locks.
      
      This is fine with the bkl:
      
            T1                       T2
      
      lock_kernel()
          mutex_lock(A)
          unlock_kernel()
          // do something
                                  lock_kernel()
                                      mutex_lock(A) -> already locked by T1
                                      schedule() (and then unlock_kernel())
          lock_kernel()
          mutex_unlock(A)
          ....
      
      This is not fine with a mutex:
      
            T1                       T2
      
      mutex_lock(write)
          mutex_lock(A)
          mutex_unlock(write)
          // do something
                                 mutex_lock(write)
                                    mutex_lock(A) -> already locked by T1
                                    schedule()
      
          mutex_lock(write) -> already locked by T2
          deadlock
      
      The solution in this patch is to provide a helper which releases the write
      lock and sleep a bit if we can't lock a mutex that depend on it. It's another
      simulation of the bkl behaviour.
      
      The last axis is to locate the fs callbacks that are called with the bkl held,
      according to Documentation/filesystem/Locking.
      
      Those are:
      
      - reiserfs_remount
      - reiserfs_fill_super
      - reiserfs_put_super
      
      Reiserfs didn't need to explicitly lock because of the context of these callbacks.
      But now we must take care of that with the new locking.
      
      After this patch, reiserfs suffers from a slight performance regression (for now).
      On UP, a high volume write with dd reports an average of 27 MB/s instead
      of 30 MB/s without the patch applied.
      Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
      Reviewed-by: default avatarIngo Molnar <mingo@elte.hu>
      Cc: Jeff Mahoney <jeffm@suse.com>
      Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: Bron Gondwana <brong@fastmail.fm>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Alexander Viro <viro@zeniv.linux.org.uk>
      LKML-Reference: <1239070789-13354-1-git-send-email-fweisbec@gmail.com>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      8ebc4232
  2. 09 Sep, 2009 3 commits
    • Linus Torvalds's avatar
      Linux 2.6.31 · 74fca6a4
      Linus Torvalds authored
      74fca6a4
    • Ed Cashin's avatar
      aoe: allocate unused request_queue for sysfs · 7135a71b
      Ed Cashin authored
      Andy Whitcroft reported an oops in aoe triggered by use of an
      incorrectly initialised request_queue object:
      
        [ 2645.959090] kobject '<NULL>' (ffff880059ca22c0): tried to add
      		an uninitialized object, something is seriously wrong.
        [ 2645.959104] Pid: 6, comm: events/0 Not tainted 2.6.31-5-generic #24-Ubuntu
        [ 2645.959107] Call Trace:
        [ 2645.959139] [<ffffffff8126ca2f>] kobject_add+0x5f/0x70
        [ 2645.959151] [<ffffffff8125b4ab>] blk_register_queue+0x8b/0xf0
        [ 2645.959155] [<ffffffff8126043f>] add_disk+0x8f/0x160
        [ 2645.959161] [<ffffffffa01673c4>] aoeblk_gdalloc+0x164/0x1c0 [aoe]
      
      The request queue of an aoe device is not used but can be allocated in
      code that does not sleep.
      
      Bruno bisected this regression down to
      
        cd43e26f
      
        block: Expose stacked device queues in sysfs
      
      "This seems to generate /sys/block/$device/queue and its contents for
       everyone who is using queues, not just for those queues that have a
       non-NULL queue->request_fn."
      
      Addresses http://bugs.launchpad.net/bugs/410198
      Addresses http://bugzilla.kernel.org/show_bug.cgi?id=13942
      
      Note that embedding a queue inside another object has always been
      an illegal construct, since the queues are reference counted and
      must persist until the last reference is dropped. So aoe was
      always buggy in this respect (Jens).
      Signed-off-by: default avatarEd Cashin <ecashin@coraid.com>
      Cc: Andy Whitcroft <apw@canonical.com>
      Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
      Cc: Bruno Premont <bonbons@linux-vserver.org>
      Cc: Martin K. Petersen <martin.petersen@oracle.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
      7135a71b
    • Linus Torvalds's avatar
      i915: disable interrupts before tearing down GEM state · e6890f6f
      Linus Torvalds authored
      Reinette Chatre reports a frozen system (with blinking keyboard LEDs)
      when switching from graphics mode to the text console, or when
      suspending (which does the same thing). With netconsole, the oops
      turned out to be
      
      	BUG: unable to handle kernel NULL pointer dereference at 0000000000000084
      	IP: [<ffffffffa03ecaab>] i915_driver_irq_handler+0x26b/0xd20 [i915]
      
      and it's due to the i915_gem.c code doing drm_irq_uninstall() after
      having done i915_gem_idle(). And the i915_gem_idle() path will do
      
        i915_gem_idle() ->
          i915_gem_cleanup_ringbuffer() ->
            i915_gem_cleanup_hws() ->
              dev_priv->hw_status_page = NULL;
      
      but if an i915 interrupt comes in after this stage, it may want to
      access that hw_status_page, and gets the above NULL pointer dereference.
      
      And since the NULL pointer dereference happens from within an interrupt,
      and with the screen still in graphics mode, the common end result is
      simply a silently hung machine.
      
      Fix it by simply uninstalling the irq handler before idling rather than
      after. Fixes
      
          http://bugzilla.kernel.org/show_bug.cgi?id=13819Reported-and-tested-by: default avatarReinette Chatre <reinette.chatre@intel.com>
      Acked-by: default avatarJesse Barnes <jbarnes@virtuousgeek.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      e6890f6f
  3. 08 Sep, 2009 1 commit
  4. 07 Sep, 2009 7 commits
  5. 06 Sep, 2009 1 commit
    • David S. Miller's avatar
      gianfar: Fix build. · d9d8e041
      David S. Miller authored
      Reported by Michael Guntsche <mike@it-loops.com>
      
      --------------------
      Commit
      38bddf04 gianfar: gfar_remove needs to call unregister_netdev()
      
      breaks the build of the gianfar driver because "dev" is undefined in
      this function. To quickly test rc9 I changed this to priv->ndev but I do
      not know if this is the correct one.
      --------------------
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      d9d8e041
  6. 05 Sep, 2009 27 commits