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  1. 14 9月, 2009 1 次提交
    • F
      reiserfs: kill-the-BKL · 8ebc4232
      由 Frederic Weisbecker 提交于 
      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: NFrederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: NIngo 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: NIngo Molnar <mingo@elte.hu>
      8ebc4232
  3. 10 9月, 2009 1 次提交
  5. 09 9月, 2009 3 次提交
    • E
      aoe: allocate unused request_queue for sysfs · 7135a71b
      由 Ed Cashin 提交于 
      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: NEd 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: NJens Axboe <jens.axboe@oracle.com>
      7135a71b
    • L
      i915: disable interrupts before tearing down GEM state · e6890f6f
      由 Linus Torvalds 提交于 
      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: NReinette Chatre <reinette.chatre@intel.com>
Acked-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      e6890f6f
    • Z
      drm/i915: fix mask bits setting · 7c8460db
      由 Zhenyu Wang 提交于 
      eDP is exclusive connector too, and add missing crtc_mask
setting for TV.

This fixes

	http://bugzilla.kernel.org/show_bug.cgi?id=14139Signed-off-by: NZhenyu Wang <zhenyuw@linux.intel.com>
Reported-and-tested-by: NCarlos R. Mafra <crmafra2@gmail.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      7c8460db
  7. 08 9月, 2009 5 次提交
  9. 07 9月, 2009 2 次提交
  11. 06 9月, 2009 28 次提交