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  1. 11 Oct, 2012 22 commits
  3. 28 Sep, 2012 2 commits
  5. 27 Sep, 2012 2 commits
  7. 26 Sep, 2012 4 commits
    • Mikulas Patocka's avatar
      percpu-rw-semaphore: fix documentation typos · e6b5c082
      Mikulas Patocka authored 
      One more patch for this thing, fixing some typos in the documentation.
Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      e6b5c082
    • Fengguang Wu's avatar
      fs/block_dev.c:1644:5: sparse: symbol 'blkdev_mmap' was not declared · 3eab7315
      Fengguang Wu authored 
      blkdev_mmap() isn't used outside of fs/block_dev.c, mark it as
static.
Reported-by: default avatarFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      3eab7315
    • Mikulas Patocka's avatar
      blockdev: turn a rw semaphore into a percpu rw semaphore · 62ac665f
      Mikulas Patocka authored 
      This avoids cache line bouncing when many processes lock the semaphore
for read.

New percpu lock implementation

The lock consists of an array of percpu unsigned integers, a boolean
variable and a mutex.

When we take the lock for read, we enter rcu read section, check for a
"locked" variable. If it is false, we increase a percpu counter on the
current cpu and exit the rcu section. If "locked" is true, we exit the
rcu section, take the mutex and drop it (this waits until a writer
finished) and retry.

Unlocking for read just decreases percpu variable. Note that we can
unlock on a difference cpu than where we locked, in this case the
counter underflows. The sum of all percpu counters represents the number
of processes that hold the lock for read.

When we need to lock for write, we take the mutex, set "locked" variable
to true and synchronize rcu. Since RCU has been synchronized, no
processes can create new read locks. We wait until the sum of percpu
counters is zero - when it is, there are no readers in the critical
section.
Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      62ac665f
    • Mikulas Patocka's avatar
      Fix a crash when block device is read and block size is changed at the same time · b87570f5
      Mikulas Patocka authored 
      The kernel may crash when block size is changed and I/O is issued
simultaneously.

Because some subsystems (udev or lvm) may read any block device anytime,
the bug actually puts any code that changes a block device size in
jeopardy.

The crash can be reproduced if you place "msleep(1000)" to
blkdev_get_blocks just before "bh->b_size = max_blocks <<
inode->i_blkbits;".
Then, run "dd if=/dev/ram0 of=/dev/null bs=4k count=1 iflag=direct"
While it is waiting in msleep, run "blockdev --setbsz 2048 /dev/ram0"
You get a BUG.

The direct and non-direct I/O is written with the assumption that block
size does not change. It doesn't seem practical to fix these crashes
one-by-one there may be many crash possibilities when block size changes
at a certain place and it is impossible to find them all and verify the
code.

This patch introduces a new rw-lock bd_block_size_semaphore. The lock is
taken for read during I/O. It is taken for write when changing block
size. Consequently, block size can't be changed while I/O is being
submitted.

For asynchronous I/O, the patch only prevents block size change while
the I/O is being submitted. The block size can change when the I/O is in
progress or when the I/O is being finished. This is acceptable because
there are no accesses to block size when asynchronous I/O is being
finished.

The patch prevents block size changing while the device is mapped with
mmap.
Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      b87570f5
  9. 21 Sep, 2012 2 commits
    • Tejun Heo's avatar
      block: fix request_queue->flags initialization · 60ea8226
      Tejun Heo authored 
      A queue newly allocated with blk_alloc_queue_node() has only
QUEUE_FLAG_BYPASS set.  For request-based drivers,
blk_init_allocated_queue() is called and q->queue_flags is overwritten
with QUEUE_FLAG_DEFAULT which doesn't include BYPASS even though the
initial bypass is still in effect.

In blk_init_allocated_queue(), or QUEUE_FLAG_DEFAULT to q->queue_flags
instead of overwriting.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org
Acked-by: default avatarVivek Goyal <vgoyal@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      60ea8226
    • Tejun Heo's avatar
      block: lift the initial queue bypass mode on blk_register_queue() instead of... · 749fefe6
      Tejun Heo authored 
      block: lift the initial queue bypass mode on blk_register_queue() instead of blk_init_allocated_queue()

b82d4b19 ("blkcg: make request_queue bypassing on allocation") made
request_queues bypassed on allocation to avoid switching on and off
bypass mode on a queue being initialized.  Some drivers allocate and
then destroy a lot of queues without fully initializing them and
incurring bypass latency overhead on each of them could add upto
significant overhead.

Unfortunately, blk_init_allocated_queue() is never used by queues of
bio-based drivers, which means that all bio-based driver queues are in
bypass mode even after initialization and registration complete
successfully.

Due to the limited way request_queues are used by bio drivers, this
problem is hidden pretty well but it shows up when blk-throttle is
used in combination with a bio-based driver.  Trying to configure
(echoing to cgroupfs file) blk-throttle for a bio-based driver hangs
indefinitely in blkg_conf_prep() waiting for bypass mode to end.

This patch moves the initial blk_queue_bypass_end() call from
blk_init_allocated_queue() to blk_register_queue() which is called for
any userland-visible queues regardless of its type.

I believe this is correct because I don't think there is any block
driver which needs or wants working elevator and blk-cgroup on a queue
which isn't visible to userland.  If there are such users, we need a
different solution.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reported-by: default avatarJoseph Glanville <joseph.glanville@orionvm.com.au>
Cc: stable@vger.kernel.org
Acked-by: default avatarVivek Goyal <vgoyal@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      749fefe6
  11. 20 Sep, 2012 5 commits
  13. 12 Sep, 2012 1 commit
    • Peter Senna Tschudin's avatar
      block/blk-tag.c: Remove useless kfree · d41570b7
      Peter Senna Tschudin authored 
      Remove useless kfree() and clean up code related to the removal.

The semantic patch that finds this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@r exists@
position p1,p2;
expression x;
@@

if (x@p1 == NULL) { ... kfree@p2(x); ... return ...; }

@unchanged exists@
position r.p1,r.p2;
expression e <= r.x,x,e1;
iterator I;
statement S;
@@

if (x@p1 == NULL) { ... when != I(x,...) S
                        when != e = e1
                        when != e += e1
                        when != e -= e1
                        when != ++e
                        when != --e
                        when != e++
                        when != e--
                        when != &e
   kfree@p2(x); ... return ...; }

@ok depends on unchanged exists@
position any r.p1;
position r.p2;
expression x;
@@

... when != true x@p1 == NULL
kfree@p2(x);

@depends on !ok && unchanged@
position r.p2;
expression x;
@@

*kfree@p2(x);
// </smpl>
Signed-off-by: default avatarPeter Senna Tschudin <peter.senna@gmail.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      d41570b7
  15. 09 Sep, 2012 2 commits
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