linux-toradex.git/fs/fs-writeback.c, branch v3.6.8

ext4: fix potential deadlock in ext4_nonda_switch()

2012-10-12T20:50:24+00:00

commit 00d4e7362ed01987183e9528295de3213031309c upstream.

In ext4_nonda_switch(), if the file system is getting full we used to
call writeback_inodes_sb_if_idle().  The problem is that we can be
holding i_mutex already, and this causes a potential deadlock when
writeback_inodes_sb_if_idle() when it tries to take s_umount.  (See
lockdep output below).

As it turns out we don't need need to hold s_umount; the fact that we
are in the middle of the write(2) system call will keep the superblock
pinned.  Unfortunately writeback_inodes_sb() checks to make sure
s_umount is taken, and the VFS uses a different mechanism for making
sure the file system doesn't get unmounted out from under us.  The
simplest way of dealing with this is to just simply grab s_umount
using a trylock, and skip kicking the writeback flusher thread in the
very unlikely case that we can't take a read lock on s_umount without
blocking.

Also, we now check the cirteria for kicking the writeback thread
before we decide to whether to fall back to non-delayed writeback, so
if there are any outstanding delayed allocation writes, we try to get
them resolved as soon as possible.

   [ INFO: possible circular locking dependency detected ]
   3.6.0-rc1-00042-gce894ca #367 Not tainted
   -------------------------------------------------------
   dd/8298 is trying to acquire lock:
    (&type->s_umount_key#18){++++..}, at: [] writeback_inodes_sb_if_idle+0x28/0x46

   but task is already holding lock:
    (&sb->s_type->i_mutex_key#8){+.+...}, at: [] generic_file_aio_write+0x5f/0xd3

   which lock already depends on the new lock.

   2 locks held by dd/8298:
    #0:  (sb_writers#2){.+.+.+}, at: [] generic_file_aio_write+0x56/0xd3
    #1:  (&sb->s_type->i_mutex_key#8){+.+...}, at: [] generic_file_aio_write+0x5f/0xd3

   stack backtrace:
   Pid: 8298, comm: dd Not tainted 3.6.0-rc1-00042-gce894ca #367
   Call Trace:
    [] ? console_unlock+0x345/0x372
    [] print_circular_bug+0x190/0x19d
    [] __lock_acquire+0x86d/0xb6c
    [] ? mark_held_locks+0x5c/0x7b
    [] lock_acquire+0x66/0xb9
    [] ? writeback_inodes_sb_if_idle+0x28/0x46
    [] down_read+0x28/0x58
    [] ? writeback_inodes_sb_if_idle+0x28/0x46
    [] writeback_inodes_sb_if_idle+0x28/0x46
    [] ext4_nonda_switch+0xe1/0xf4
    [] ext4_da_write_begin+0x27/0x193
    [] generic_file_buffered_write+0xc8/0x1bb
    [] __generic_file_aio_write+0x1dd/0x205
    [] generic_file_aio_write+0x78/0xd3
    [] ext4_file_write+0x480/0x4a6
    [] ? __lock_acquire+0x41e/0xb6c
    [] ? sched_clock_cpu+0x11a/0x13e
    [] ? trace_hardirqs_off+0xb/0xd
    [] ? local_clock+0x37/0x4e
    [] do_sync_write+0x67/0x9d
    [] ? wait_on_retry_sync_kiocb+0x44/0x44
    [] vfs_write+0x7b/0xe6
    [] sys_write+0x3b/0x64
    [] syscall_call+0x7/0xb

Signed-off-by: "Theodore Ts'o" 
Signed-off-by: Greg Kroah-Hartman

mm: prepare for removal of obsolete /proc/sys/vm/nr_pdflush_threads

2012-08-01T01:42:40+00:00

Since per-BDI flusher threads were introduced in 2.6, the pdflush
mechanism is not used any more.  But the old interface exported through
/proc/sys/vm/nr_pdflush_threads still exists and is obviously useless.

For back-compatibility, printk warning information and return 2 to notify
the users that the interface is removed.

Signed-off-by: Wanpeng Li 
Cc: Wu Fengguang 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Merge tag 'writeback-proportions' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux

2012-07-31T05:14:04+00:00

Pull writeback updates from Wu Fengguang:
 "Use time based periods to age the writeback proportions, which can
  adapt equally well to fast/slow devices."

Fix up trivial conflict in comment in fs/sync.c

* tag 'writeback-proportions' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux:
  writeback: Fix some comment errors
  block: Convert BDI proportion calculations to flexible proportions
  lib: Fix possible deadlock in flexible proportion code
  lib: Proportions with flexible period

vfs: Move noop_backing_dev_info check from sync into writeback

2012-07-22T19:58:18+00:00

In principle, a filesystem may want to have ->sync_fs() called during sync(1)
although it does not have a bdi (i.e. s_bdi is set to noop_backing_dev_info).
Only writeback code really needs bdi set to something reasonable. So move the
checks where they are more logical.

Reviewed-by: Christoph Hellwig 
Signed-off-by: Jan Kara 
Signed-off-by: Al Viro

writeback: Fix some comment errors

2012-06-09T11:54:47+00:00

Signed-off-by: Wanpeng Li 
Signed-off-by: Fengguang Wu

writeback: Fix lock imbalance in writeback_sb_inodes()

2012-06-08T23:32:15+00:00

Fix bug introduced by 169ebd90.  We have to have wb_list_lock locked when
restarting writeback loop after having waited for inode writeback.

Bug description by Ted Tso:

  I can reproduce this fairly easily by using ext4 w/o a journal, running
  under KVM with 1024megs memory, with fsstress (xfstests #13):

  [   45.153294] =====================================
  [   45.154784] [ BUG: bad unlock balance detected! ]
  [   45.155591] 3.5.0-rc1-00002-gb22b1f1 #124 Not tainted
  [   45.155591] -------------------------------------
  [   45.155591] flush-254:16/2499 is trying to release lock (&(&wb->list_lock)->rlock) at:
  [   45.155591] [] writeback_sb_inodes+0x160/0x327
  [   45.155591] but there are no more locks to release!

Reported-by: Theodore Ts'o 
Tested-by: Theodore Ts'o 
Signed-off-by: Jan Kara 
Signed-off-by: Fengguang Wu

writeback: Avoid iput() from flusher thread

2012-05-06T05:43:41+00:00

Doing iput() from flusher thread (writeback_sb_inodes()) can create problems
because iput() can do a lot of work - for example truncate the inode if it's
the last iput on unlinked file. Some filesystems depend on flusher thread
progressing (e.g. because they need to flush delay allocated blocks to reduce
allocation uncertainty) and so flusher thread doing truncate creates
interesting dependencies and possibilities for deadlocks.

We get rid of iput() in flusher thread by using the fact that I_SYNC inode
flag effectively pins the inode in memory. So if we take care to either hold
i_lock or have I_SYNC set, we can get away without taking inode reference
in writeback_sb_inodes().

As a side effect of these changes, we also fix possible use-after-free in
wb_writeback() because inode_wait_for_writeback() call could try to reacquire
i_lock on the inode that was already free.

Signed-off-by: Jan Kara 
Signed-off-by: Fengguang Wu

writeback: Refactor writeback_single_inode()

2012-05-06T05:43:40+00:00

The code in writeback_single_inode() is relatively complex. The list requeing
logic makes sense only for flusher thread but not really for sync_inode() or
write_inode_now() callers. Also when we want to get rid of inode references
held by flusher thread, we will need a special I_SYNC handling there.

So separate part of writeback_single_inode() which does the real writeback work
into __writeback_single_inode() and make writeback_single_inode() do only stuff
necessary for callers writing only one inode, moving the special list handling
into writeback_sb_inodes(). As a sideeffect this fixes a possible race where we
could skip some inode during sync(2) because other writer refiled it from b_io
to b_dirty list. Also I_SYNC handling is moved into the callers of
__writeback_single_inode() to make locking easier.

Reviewed-by: Christoph Hellwig 
Signed-off-by: Jan Kara 
Signed-off-by: Fengguang Wu

writeback: Remove wb->list_lock from writeback_single_inode()

2012-05-06T05:43:39+00:00

writeback_single_inode() doesn't need wb->list_lock for anything on entry now.
So remove the requirement. This makes locking of writeback_single_inode()
temporarily awkward (entering with i_lock, returning with i_lock and
wb->list_lock) but it will be sanitized in the next patch.

Also inode_wait_for_writeback() doesn't need wb->list_lock for anything. It was
just taking it to make usage convenient for callers but with
writeback_single_inode() changing it's not very convenient anymore. So remove
the lock from that function.

Reviewed-by: Christoph Hellwig 
Signed-off-by: Jan Kara 
Signed-off-by: Fengguang Wu

writeback: Separate inode requeueing after writeback

2012-05-06T05:43:39+00:00

Move inode requeueing after inode has been written out into a separate
function.

Reviewed-by: Christoph Hellwig 
Signed-off-by: Jan Kara 
Signed-off-by: Fengguang Wu