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  1. 27 9月, 2014 6 次提交
  3. 14 9月, 2014 2 次提交
    • A
      move the call of __d_drop(anon) into __d_materialise_unique(dentry, anon) · 6f18493e
      由 Al Viro 提交于 
      and lock the right list there

Cc: stable@vger.kernel.org
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      6f18493e
    • L
      vfs: fix bad hashing of dentries · 99d263d4
      由 Linus Torvalds 提交于 
      Josef Bacik found a performance regression between 3.2 and 3.10 and
narrowed it down to commit bfcfaa77 ("vfs: use 'unsigned long'
accesses for dcache name comparison and hashing"). He reports:

 "The test case is essentially

      for (i = 0; i < 1000000; i++)
              mkdir("a$i");

  On xfs on a fio card this goes at about 20k dir/sec with 3.2, and 12k
  dir/sec with 3.10.  This is because we spend waaaaay more time in
  __d_lookup on 3.10 than in 3.2.

  The new hashing function for strings is suboptimal for <
  sizeof(unsigned long) string names (and hell even > sizeof(unsigned
  long) string names that I've tested).  I broke out the old hashing
  function and the new one into a userspace helper to get real numbers
  and this is what I'm getting:

      Old hash table had 1000000 entries, 0 dupes, 0 max dupes
      New hash table had 12628 entries, 987372 dupes, 900 max dupes
      We had 11400 buckets with a p50 of 30 dupes, p90 of 240 dupes, p99 of 567 dupes for the new hash

  My test does the hash, and then does the d_hash into a integer pointer
  array the same size as the dentry hash table on my system, and then
  just increments the value at the address we got to see how many
  entries we overlap with.

  As you can see the old hash function ended up with all 1 million
  entries in their own bucket, whereas the new one they are only
  distributed among ~12.5k buckets, which is why we're using so much
  more CPU in __d_lookup".

The reason for this hash regression is two-fold:

 - On 64-bit architectures the down-mixing of the original 64-bit
   word-at-a-time hash into the final 32-bit hash value is very
   simplistic and suboptimal, and just adds the two 32-bit parts
   together.

   In particular, because there is no bit shuffling and the mixing
   boundary is also a byte boundary, similar character patterns in the
   low and high word easily end up just canceling each other out.

 - the old byte-at-a-time hash mixed each byte into the final hash as it
   hashed the path component name, resulting in the low bits of the hash
   generally being a good source of hash data.  That is not true for the
   word-at-a-time case, and the hash data is distributed among all the
   bits.

The fix is the same in both cases: do a better job of mixing the bits up
and using as much of the hash data as possible.  We already have the
"hash_32|64()" functions to do that.
Reported-by: NJosef Bacik <jbacik@fb.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Chris Mason <clm@fb.com>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      99d263d4
  5. 08 8月, 2014 9 次提交
  7. 12 6月, 2014 1 次提交
    • A
      lock_parent: don't step on stale ->d_parent of all-but-freed one · c2338f2d
      由 Al Viro 提交于 
      Dentry that had been through (or into) __dentry_kill() might be seen
by shrink_dentry_list(); that's normal, it'll be taken off the shrink
list and freed if __dentry_kill() has already finished.  The problem
is, its ->d_parent might be pointing to already freed dentry, so
lock_parent() needs to be careful.

We need to check that dentry hasn't already gone into __dentry_kill()
*and* grab rcu_read_lock() before dropping ->d_lock - the latter makes
sure that whatever we see in ->d_parent after dropping ->d_lock it
won't be freed until we drop rcu_read_lock().
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      c2338f2d
  9. 07 6月, 2014 1 次提交
  11. 01 6月, 2014 1 次提交
    • L
      dcache: add missing lockdep annotation · 9f12600f
      由 Linus Torvalds 提交于 
      lock_parent() very much on purpose does nested locking of dentries, and
is careful to maintain the right order (lock parent first).  But because
it didn't annotate the nested locking order, lockdep thought it might be
a deadlock on d_lock, and complained.

Add the proper annotation for the inner locking of the child dentry to
make lockdep happy.

Introduced by commit 046b961b ("shrink_dentry_list(): take parent's
->d_lock earlier").
Reported-and-tested-by: NJosh Boyer <jwboyer@fedoraproject.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      9f12600f
  13. 30 5月, 2014 3 次提交
    • A
      dentry_kill() doesn't need the second argument now · 8cbf74da
      由 Al Viro 提交于 
      it's 1 in the only remaining caller.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      8cbf74da
    • A
      dealing with the rest of shrink_dentry_list() livelock · b2b80195
      由 Al Viro 提交于 
      We have the same problem with ->d_lock order in the inner loop, where
we are dropping references to ancestors.  Same solution, basically -
instead of using dentry_kill() we use lock_parent() (introduced in the
previous commit) to get that lock in a safe way, recheck ->d_count
(in case if lock_parent() has ended up dropping and retaking ->d_lock
and somebody managed to grab a reference during that window), trylock
the inode->i_lock and use __dentry_kill() to do the rest.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      b2b80195
    • A
      shrink_dentry_list(): take parent's ->d_lock earlier · 046b961b
      由 Al Viro 提交于 
      The cause of livelocks there is that we are taking ->d_lock on
dentry and its parent in the wrong order, forcing us to use
trylock on the parent's one.  d_walk() takes them in the right
order, and unfortunately it's not hard to create a situation
when shrink_dentry_list() can't make progress since trylock
keeps failing, and shrink_dcache_parent() or check_submounts_and_drop()
keeps calling d_walk() disrupting the very shrink_dentry_list() it's
waiting for.

Solution is straightforward - if that trylock fails, let's unlock
the dentry itself and take locks in the right order.  We need to
stabilize ->d_parent without holding ->d_lock, but that's doable
using RCU.  And we'd better do that in the very beginning of the
loop in shrink_dentry_list(), since the checks on refcount, etc.
would need to be redone anyway.

That deals with a half of the problem - killing dentries on the
shrink list itself.  Another one (dropping their parents) is
in the next commit.

locking parent is interesting - it would be easy to do rcu_read_lock(),
lock whatever we think is a parent, lock dentry itself and check
if the parent is still the right one.  Except that we need to check
that *before* locking the dentry, or we are risking taking ->d_lock
out of order.  Fortunately, once the D1 is locked, we can check if
D2->d_parent is equal to D1 without the need to lock D2; D2->d_parent
can start or stop pointing to D1 only under D1->d_lock, so taking
D1->d_lock is enough.  In other words, the right solution is
rcu_read_lock/lock what looks like parent right now/check if it's
still our parent/rcu_read_unlock/lock the child.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      046b961b
  15. 29 5月, 2014 2 次提交
  17. 28 5月, 2014 1 次提交
  19. 04 5月, 2014 3 次提交
    • M
      dcache: don't need rcu in shrink_dentry_list() · 60942f2f
      由 Miklos Szeredi 提交于 
      Since now the shrink list is private and nobody can free the dentry while
it is on the shrink list, we can remove RCU protection from this.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      60942f2f
    • A
      more graceful recovery in umount_collect() · 9c8c10e2
      由 Al Viro 提交于 
      Start with shrink_dcache_parent(), then scan what remains.

First of all, BUG() is very much an overkill here; we are holding
->s_umount, and hitting BUG() means that a lot of interesting stuff
will be hanging after that point (sync(2), for example).  Moreover,
in cases when there had been more than one leak, we'll be better
off reporting all of them.  And more than just the last component
of pathname - %pd is there for just such uses...

That was the last user of dentry_lru_del(), so kill it off...
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      9c8c10e2
    • A
      don't remove from shrink list in select_collect() · fe91522a
      由 Al Viro 提交于 
      	If we find something already on a shrink list, just increment
data->found and do nothing else.  Loops in shrink_dcache_parent() and
check_submounts_and_drop() will do the right thing - everything we
did put into our list will be evicted and if there had been nothing,
but data->found got non-zero, well, we have somebody else shrinking
those guys; just try again.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      fe91522a
  21. 01 5月, 2014 5 次提交
  23. 20 4月, 2014 1 次提交
    • A
      fix races between __d_instantiate() and checks of dentry flags · 22213318
      由 Al Viro 提交于 
      in non-lazy walk we need to be careful about dentry switching from
negative to positive - both ->d_flags and ->d_inode are updated,
and in some places we might see only one store.  The cases where
dentry has been obtained by dcache lookup with ->i_mutex held on
parent are safe - ->d_lock and ->i_mutex provide all the barriers
we need.  However, there are several places where we run into
trouble:
	* do_last() fetches ->d_inode, then checks ->d_flags and
assumes that inode won't be NULL unless d_is_negative() is true.
Race with e.g. creat() - we might have fetched the old value of
->d_inode (still NULL) and new value of ->d_flags (already not
DCACHE_MISS_TYPE).  Lin Ming has observed and reported the resulting
oops.
	* a bunch of places checks ->d_inode for being non-NULL,
then checks ->d_flags for "is it a symlink".  Race with symlink(2)
in case if our CPU sees ->d_inode update first - we see non-NULL
there, but ->d_flags still contains DCACHE_MISS_TYPE instead of
DCACHE_SYMLINK_TYPE.  Result: false negative on "should we follow
link here?", with subsequent unpleasantness.

Cc: stable@vger.kernel.org # 3.13 and 3.14 need that one
Reported-and-tested-by: NLin Ming <minggr@gmail.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      22213318
  25. 01 4月, 2014 1 次提交
  27. 23 3月, 2014 1 次提交
  29. 16 3月, 2014 1 次提交
    • D
      drm: add pseudo filesystem for shared inodes · 31bbe16f
      由 David Herrmann 提交于 
      Our current DRM design uses a single address_space for all users of the
same DRM device. However, there is no way to create an anonymous
address_space without an underlying inode. Therefore, we wait for the
first ->open() callback on a registered char-dev and take-over the inode
of the char-dev. This worked well so far, but has several drawbacks:
 - We screw with FS internals and rely on some non-obvious invariants like
   inode->i_mapping being the same as inode->i_data for char-devs.
 - We don't have any address_space prior to the first ->open() from
   user-space. This leads to ugly fallback code and we cannot allocate
   global objects early.

As pointed out by Al-Viro, fs/anon_inode.c is *not* supposed to be used by
drivers for anonymous inode-allocation. Therefore, this patch follows the
proposed alternative solution and adds a pseudo filesystem mount-point to
DRM. We can then allocate private inodes including a private address_space
for each DRM device at initialization time.

Note that we could use:
  sysfs_get_inode(sysfs_mnt->mnt_sb, drm_device->dev->kobj.sd);
to get access to the underlying sysfs-inode of a "struct device" object.
However, most of this information is currently hidden and it's not clear
whether this address_space is suitable for driver access. Thus, unless
linux allows anonymous address_space objects or driver-core provides a
public inode per device, we're left with our own private internal mount
point.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NDavid Herrmann <dh.herrmann@gmail.com>
      31bbe16f
  31. 27 1月, 2014 1 次提交
  33. 26 1月, 2014 1 次提交
    • E
      vfs: Remove second variable named error in __dentry_path · a8323da0
      由 Eric W. Biederman 提交于 
      In commit  232d2d60
Author: Waiman Long <Waiman.Long@hp.com>
Date:   Mon Sep 9 12:18:13 2013 -0400

    dcache: Translating dentry into pathname without taking rename_lock

The __dentry_path locking was changed and the variable error was
intended to be moved outside of the loop.  Unfortunately the inner
declaration of error was not removed. Resulting in a version of
__dentry_path that will never return an error.

Remove the problematic inner declaration of error and allow
__dentry_path to return errors once again.

Cc: stable@vger.kernel.org
Cc: Waiman Long <Waiman.Long@hp.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      a8323da0