linux.git/fs/nilfs2/segment.c, branch v4.5

nilfs2: fix gcc unused-but-set-variable warnings

2015-11-07T01:50:42+00:00

Fix the following build warnings:

 $ make W=1
 [...]
   CC [M]  fs/nilfs2/btree.o
 fs/nilfs2/btree.c: In function 'nilfs_btree_split':
 fs/nilfs2/btree.c:923:8: warning: variable 'newptr' set but not used [-Wunused-but-set-variable]
   __u64 newptr;
         ^
 fs/nilfs2/btree.c:922:8: warning: variable 'newkey' set but not used [-Wunused-but-set-variable]
   __u64 newkey;
         ^
   CC [M]  fs/nilfs2/dat.o
 fs/nilfs2/dat.c: In function 'nilfs_dat_prepare_end':
 fs/nilfs2/dat.c:158:8: warning: variable 'start' set but not used [-Wunused-but-set-variable]
   __u64 start;
         ^
   CC [M]  fs/nilfs2/segment.o
 fs/nilfs2/segment.c: In function 'nilfs_segctor_do_immediate_flush':
 fs/nilfs2/segment.c:2433:6: warning: variable 'err' set but not used [-Wunused-but-set-variable]
   int err;
       ^
   CC [M]  fs/nilfs2/sufile.o
 fs/nilfs2/sufile.c: In function 'nilfs_sufile_alloc':
 fs/nilfs2/sufile.c:320:27: warning: variable 'ncleansegs' set but not used [-Wunused-but-set-variable]
   unsigned long nsegments, ncleansegs, nsus, cnt;
                            ^
   CC [M]  fs/nilfs2/alloc.o
 fs/nilfs2/alloc.c: In function 'nilfs_palloc_prepare_alloc_entry':
 fs/nilfs2/alloc.c:478:38: warning: variable 'groups_per_desc_block' set but not used [-Wunused-but-set-variable]
   unsigned long n, entries_per_group, groups_per_desc_block;
                                       ^

Signed-off-by: Ryusuke Konishi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

nilfs2: add a tracepoint for transaction events

2015-11-07T01:50:42+00:00

This patch adds a tracepoint for transaction events of nilfs.  With the
tracepoint, these events can be tracked: begin, abort, commit, trylock,
lock, and unlock.  Basically, these events have corresponding functions
e.g.  begin event corresponds nilfs_transaction_begin().  The unlock event
is an exception.  It corresponds to the iteration in
nilfs_transaction_lock().

Only one tracepoint is introcued: nilfs2_transaction_transition.  The
above events are distinguished with newly introduced enum.  With this
tracepoint, we can analyse a critical section of segment constructoin.

Sample output by tpoint of perf-tools:
              cp-4457  [000] ...1    63.266220: nilfs2_transaction_transition: sb = ffff8802112b8800 ti = ffff8800bf5ccc58 count = 1 flags = 9 state = BEGIN
              cp-4457  [000] ...1    63.266221: nilfs2_transaction_transition: sb = ffff8802112b8800 ti = ffff8800bf5ccc58 count = 0 flags = 9 state = COMMIT
              cp-4457  [000] ...1    63.266221: nilfs2_transaction_transition: sb = ffff8802112b8800 ti = ffff8800bf5ccc58 count = 0 flags = 9 state = COMMIT
        segctord-4371  [001] ...1    68.261196: nilfs2_transaction_transition: sb = ffff8802112b8800 ti = ffff8800b889bdf8 count = 0 flags = 10 state = TRYLOCK
        segctord-4371  [001] ...1    68.261280: nilfs2_transaction_transition: sb = ffff8802112b8800 ti = ffff8800b889bdf8 count = 0 flags = 10 state = LOCK
        segctord-4371  [001] ...1    68.261877: nilfs2_transaction_transition: sb = ffff8802112b8800 ti = ffff8800b889bdf8 count = 1 flags = 10 state = BEGIN
        segctord-4371  [001] ...1    68.262116: nilfs2_transaction_transition: sb = ffff8802112b8800 ti = ffff8800b889bdf8 count = 0 flags = 18 state = COMMIT
        segctord-4371  [001] ...1    68.265032: nilfs2_transaction_transition: sb = ffff8802112b8800 ti = ffff8800b889bdf8 count = 0 flags = 18 state = UNLOCK
        segctord-4371  [001] ...1   132.376847: nilfs2_transaction_transition: sb = ffff8802112b8800 ti = ffff8800b889bdf8 count = 0 flags = 10 state = TRYLOCK

This patch also does trivial cleaning of comma usage in collection stage
transition event for consistent coding style.

Signed-off-by: Hitoshi Mitake 
Signed-off-by: Ryusuke Konishi 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

nilfs2: add a tracepoint for tracking stage transition of segment construction

2015-11-07T01:50:42+00:00

This patch adds a tracepoint for tracking stage transition of block
collection in segment construction.  With the tracepoint, we can analysis
the behavior of segment construction in depth.  It would be useful for
bottleneck detection and debugging, etc.

The tracepoint is created with the standard trace API of linux (like ext3,
ext4, f2fs and btrfs).  So we can analysis with existing tools easily.  Of
course, more detailed analysis will be possible if we can create nilfs
specific analysis tools.

Below is an example of event dump with Brendan Gregg's perf-tools
(https://github.com/brendangregg/perf-tools).  Time consumption between
each stage can be obtained.

$ sudo bin/tpoint nilfs2:nilfs2_collection_stage_transition
Tracing nilfs2:nilfs2_collection_stage_transition. Ctrl-C to end.
        segctord-14875 [003] ...1 28311.067794: nilfs2_collection_stage_transition: sci = ffff8800ce6de000 stage = ST_INIT
        segctord-14875 [003] ...1 28311.068139: nilfs2_collection_stage_transition: sci = ffff8800ce6de000 stage = ST_GC
        segctord-14875 [003] ...1 28311.068139: nilfs2_collection_stage_transition: sci = ffff8800ce6de000 stage = ST_FILE
        segctord-14875 [003] ...1 28311.068486: nilfs2_collection_stage_transition: sci = ffff8800ce6de000 stage = ST_IFILE
        segctord-14875 [003] ...1 28311.068540: nilfs2_collection_stage_transition: sci = ffff8800ce6de000 stage = ST_CPFILE
        segctord-14875 [003] ...1 28311.068561: nilfs2_collection_stage_transition: sci = ffff8800ce6de000 stage = ST_SUFILE
        segctord-14875 [003] ...1 28311.068565: nilfs2_collection_stage_transition: sci = ffff8800ce6de000 stage = ST_DAT
        segctord-14875 [003] ...1 28311.068573: nilfs2_collection_stage_transition: sci = ffff8800ce6de000 stage = ST_SR
        segctord-14875 [003] ...1 28311.068574: nilfs2_collection_stage_transition: sci = ffff8800ce6de000 stage = ST_DONE

For capturing transition correctly, this patch adds wrappers for the
member scnt of nilfs_cstage.  With this change, every transition of the
stage can produce trace event in a correct manner.

Signed-off-by: Hitoshi Mitake 
Signed-off-by: Ryusuke Konishi 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

nilfs2: use set_mask_bits() for operations on buffer state bitmap

2015-04-17T13:04:03+00:00

nilfs_forget_buffer(), nilfs_clear_dirty_page(), and
nilfs_segctor_complete_write() are using a bunch of atomic bit operations
against buffer state bitmap.

This reduces the number of them by utilizing set_mask_bits() macro.

Signed-off-by: Ryusuke Konishi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

nilfs2: do not use async write flag for segment summary buffers

2015-04-17T13:04:03+00:00

The async write flag is introduced to nilfs2 in the commit 7f42ec394156
("nilfs2: fix issue with race condition of competition between segments
for dirty blocks"), but the flag only makes sense for data buffers and
btree node buffers.  It is not needed for segment summary buffers.

This gets rid of the latter uses as part of refactoring of atomic bit
operations on buffer state bitmap.

Signed-off-by: Ryusuke Konishi 
Cc: Vyacheslav Dubeyko 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

nilfs2: fix deadlock of segment constructor during recovery

2015-03-13T01:46:08+00:00

According to a report from Yuxuan Shui, nilfs2 in kernel 3.19 got stuck
during recovery at mount time.  The code path that caused the deadlock was
as follows:

  nilfs_fill_super()
    load_nilfs()
      nilfs_salvage_orphan_logs()
        * Do roll-forwarding, attach segment constructor for recovery,
          and kick it.

        nilfs_segctor_thread()
          nilfs_segctor_thread_construct()
           * A lock is held with nilfs_transaction_lock()
             nilfs_segctor_do_construct()
               nilfs_segctor_drop_written_files()
                 iput()
                   iput_final()
                     write_inode_now()
                       writeback_single_inode()
                         __writeback_single_inode()
                           do_writepages()
                             nilfs_writepage()
                               nilfs_construct_dsync_segment()
                                 nilfs_transaction_lock() --> deadlock

This can happen if commit 7ef3ff2fea8b ("nilfs2: fix deadlock of segment
constructor over I_SYNC flag") is applied and roll-forward recovery was
performed at mount time.  The roll-forward recovery can happen if datasync
write is done and the file system crashes immediately after that.  For
instance, we can reproduce the issue with the following steps:

 < nilfs2 is mounted on /nilfs (device: /dev/sdb1) >
 # dd if=/dev/zero of=/nilfs/test bs=4k count=1 && sync
 # dd if=/dev/zero of=/nilfs/test conv=notrunc oflag=dsync bs=4k
 count=1 && reboot -nfh
 < the system will immediately reboot >
 # mount -t nilfs2 /dev/sdb1 /nilfs

The deadlock occurs because iput() can run segment constructor through
writeback_single_inode() if MS_ACTIVE flag is not set on sb->s_flags.  The
above commit changed segment constructor so that it calls iput()
asynchronously for inodes with i_nlink == 0, but that change was
imperfect.

This fixes the another deadlock by deferring iput() in segment constructor
even for the case that mount is not finished, that is, for the case that
MS_ACTIVE flag is not set.

Signed-off-by: Ryusuke Konishi 
Reported-by: Yuxuan Shui 
Tested-by: Ryusuke Konishi 
Cc: Al Viro 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

nilfs2: fix deadlock of segment constructor over I_SYNC flag

2015-02-05T21:35:29+00:00

Nilfs2 eventually hangs in a stress test with fsstress program.  This
issue was caused by the following deadlock over I_SYNC flag between
nilfs_segctor_thread() and writeback_sb_inodes():

  nilfs_segctor_thread()
    nilfs_segctor_thread_construct()
      nilfs_segctor_unlock()
        nilfs_dispose_list()
          iput()
            iput_final()
              evict()
                inode_wait_for_writeback()  * wait for I_SYNC flag

  writeback_sb_inodes()
     * set I_SYNC flag on inode->i_state
    __writeback_single_inode()
      do_writepages()
        nilfs_writepages()
          nilfs_construct_dsync_segment()
            nilfs_segctor_sync()
               * wait for completion of segment constructor
    inode_sync_complete()
       * clear I_SYNC flag after __writeback_single_inode() completed

writeback_sb_inodes() calls do_writepages() for dirty inodes after
setting I_SYNC flag on inode->i_state.  do_writepages() in turn calls
nilfs_writepages(), which can run segment constructor and wait for its
completion.  On the other hand, segment constructor calls iput(), which
can call evict() and wait for the I_SYNC flag on
inode_wait_for_writeback().

Since segment constructor doesn't know when I_SYNC will be set, it
cannot know whether iput() will block or not unless inode->i_nlink has a
non-zero count.  We can prevent evict() from being called in iput() by
implementing sop->drop_inode(), but it's not preferable to leave inodes
with i_nlink == 0 for long periods because it even defers file
truncation and inode deallocation.  So, this instead resolves the
deadlock by calling iput() asynchronously with a workqueue for inodes
with i_nlink == 0.

Signed-off-by: Ryusuke Konishi 
Cc: Al Viro 
Tested-by: Ryusuke Konishi 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

nilfs2: improve the performance of fdatasync()

2014-10-14T00:18:20+00:00

Support for fdatasync() has been implemented in NILFS2 for a long time,
but whenever the corresponding inode is dirty the implementation falls
back to a full-flegded sync().  Since every write operation has to
update the modification time of the file, the inode will almost always
be dirty and fdatasync() will fall back to sync() most of the time.  But
this fallback is only necessary for a change of the file size and not
for a change of the various timestamps.

This patch adds a new flag NILFS_I_INODE_SYNC to differentiate between
those two situations.

 * If it is set the file size was changed and a full sync is necessary.
 * If it is not set then only the timestamps were updated and
   fdatasync() can go ahead.

There is already a similar flag I_DIRTY_DATASYNC on the VFS layer with
the exact same semantics.  Unfortunately it cannot be used directly,
because NILFS2 doesn't implement write_inode() and doesn't clear the VFS
flags when inodes are written out.  So the VFS writeback thread can
clear I_DIRTY_DATASYNC at any time without notifying NILFS2.  So
I_DIRTY_DATASYNC has to be mapped onto NILFS_I_INODE_SYNC in
nilfs_update_inode().

Signed-off-by: Andreas Rohner 
Signed-off-by: Ryusuke Konishi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

nilfs2: add missing blkdev_issue_flush() to nilfs_sync_fs()

2014-10-14T00:18:20+00:00

Under normal circumstances nilfs_sync_fs() writes out the super block,
which causes a flush of the underlying block device.  But this depends
on the THE_NILFS_SB_DIRTY flag, which is only set if the pointer to the
last segment crosses a segment boundary.  So if only a small amount of
data is written before the call to nilfs_sync_fs(), no flush of the
block device occurs.

In the above case an additional call to blkdev_issue_flush() is needed.
To prevent unnecessary overhead, the new flag nilfs->ns_flushed_device
is introduced, which is cleared whenever new logs are written and set
whenever the block device is flushed.  For convenience the function
nilfs_flush_device() is added, which contains the above logic.

Signed-off-by: Andreas Rohner 
Signed-off-by: Ryusuke Konishi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

nilfs2: fix segctor bug that causes file system corruption

2014-01-15T07:19:42+00:00

There is a bug in the function nilfs_segctor_collect, which results in
active data being written to a segment, that is marked as clean.  It is
possible, that this segment is selected for a later segment
construction, whereby the old data is overwritten.

The problem shows itself with the following kernel log message:

  nilfs_sufile_do_cancel_free: segment 6533 must be clean

Usually a few hours later the file system gets corrupted:

  NILFS: bad btree node (blocknr=8748107): level = 0, flags = 0x0, nchildren = 0
  NILFS error (device sdc1): nilfs_bmap_last_key: broken bmap (inode number=114660)

The issue can be reproduced with a file system that is nearly full and
with the cleaner running, while some IO intensive task is running.
Although it is quite hard to reproduce.

This is what happens:

 1. The cleaner starts the segment construction
 2. nilfs_segctor_collect is called
 3. sc_stage is on NILFS_ST_SUFILE and segments are freed
 4. sc_stage is on NILFS_ST_DAT current segment is full
 5. nilfs_segctor_extend_segments is called, which
    allocates a new segment
 6. The new segment is one of the segments freed in step 3
 7. nilfs_sufile_cancel_freev is called and produces an error message
 8. Loop around and the collection starts again
 9. sc_stage is on NILFS_ST_SUFILE and segments are freed
    including the newly allocated segment, which will contain active
    data and can be allocated at a later time
10. A few hours later another segment construction allocates the
    segment and causes file system corruption

This can be prevented by simply reordering the statements.  If
nilfs_sufile_cancel_freev is called before nilfs_segctor_extend_segments
the freed segments are marked as dirty and cannot be allocated any more.

Signed-off-by: Andreas Rohner 
Reviewed-by: Ryusuke Konishi 
Tested-by: Andreas Rohner 
Signed-off-by: Ryusuke Konishi 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds