linux.git/fs/btrfs/async-thread.c, branch v2.6.32

Btrfs: fix deadlock on async thread startup

2009-10-05T13:44:45+00:00

The btrfs async worker threads are used for a wide variety of things,
including processing bio end_io functions.  This means that when
the endio threads aren't running, the rest of the FS isn't
able to do the final processing required to clear PageWriteback.

The endio threads also try to exit as they become idle and
start more as the work piles up.  The problem is that starting more
threads means kthreadd may need to allocate ram, and that allocation
may wait until the global number of writeback pages on the system is
below a certain limit.

The result of that throttling is that end IO threads wait on
kthreadd, who is waiting on IO to end, which will never happen.

This commit fixes the deadlock by handing off thread startup to a
dedicated thread.  It also fixes a bug where the on-demand thread
creation was creating far too many threads because it didn't take into
account threads being started by other procs.

Signed-off-by: Chris Mason

Btrfs: Fix async thread shutdown race

2009-09-16T00:20:17+00:00

It was possible for an async worker thread to be selected to
receive a new work item, but exit before the work item was
actually placed into that thread's work list.

This commit fixes the race by incrementing the num_pending
counter earlier, and making sure to check the number of pending
work items before a thread exits.

Signed-off-by: Chris Mason

Btrfs: fix worker thread double spin_lock_irq

2009-09-16T00:20:17+00:00

The exit-on-idle code for async worker threads was incorrectly
calling spin_lock_irq with interrupts already off.

Signed-off-by: Chris Mason

Btrfs: fix async worker startup race

2009-09-16T00:20:16+00:00

After a new worker thread starts, it is placed into the
list of idle threads.  But, this may race with a
check for idle done by the worker thread itself, resulting
in a double list_add operation.

This fix adds a check to make sure the idle thread addition
is done properly.

Signed-off-by: Chris Mason

Btrfs: reduce worker thread spin_lock_irq hold times

2009-09-11T17:31:04+00:00

This changes the btrfs worker threads to batch work items
into a local list.  It allows us to pull work items in
large chunks and significantly reduces the number of times we
need to take the worker thread spinlock.

Signed-off-by: Chris Mason

Btrfs: keep irqs on more often in the worker threads

2009-09-11T17:31:04+00:00

The btrfs worker thread spinlock was being used both for the
queueing of IO and for the processing of ordered events.

The ordered events never happen from end_io handlers, and so they
don't need to use the _irq version of spinlocks.  This adds a
dedicated lock to the ordered lists so they don't have to run
with irqs off.

Signed-off-by: Chris Mason

Btrfs: Allow worker threads to exit when idle

2009-09-11T17:30:56+00:00

The Btrfs worker threads don't currently die off after they have
been idle for a while, leading to a lot of threads sitting around
doing nothing for each mount.

Also, they are unable to start atomically (from end_io hanlders).

This commit reworks the worker threads so they can be started
from end_io handlers (just setting a flag that asks for a thread
to be added at a later date) and so they can exit if they
have been idle for a long time.

Signed-off-by: Chris Mason

Btrfs: convert nested spin_lock_irqsave to spin_lock

2009-07-22T20:49:00+00:00

If spin_lock_irqsave is called twice in a row with the same second
argument, the interrupt state at the point of the second call overwrites
the value saved by the first call.  Indeed, the second call does not need
to save the interrupt state, so it is changed to a simple spin_lock.

Signed-off-by: Julia Lawall 
Signed-off-by: Chris Mason

Btrfs: fix use after free in btrfs_start_workers fail path

2009-07-02T17:50:58+00:00

worker memory is already freed on one fail path in btrfs_start_workers,
but is still dereferenced. Switch the dereference and kfree.

Signed-off-by: Jiri Slaby 
Signed-off-by: Chris Mason

Btrfs: init worker struct fields before kthread-run

2009-06-11T00:11:29+00:00

This patch fixes a bug which may result race condition
between btrfs_start_workers() and worker_loop().

btrfs_start_workers() executed in a parent thread writes
on workers->worker and worker_loop() in a child thread
reads workers->worker. However, there is no synchronization
enforcing the order of two operations.

This patch makes btrfs_start_workers() fill workers->worker
before it starts a child thread with worker_loop()

Signed-off-by: Chris Mason