ext4: fix unjournalled bg descriptor while initializing inode bitmap

The first time that we allocate from an uninitialized inode allocation
bitmap, if the block allocation bitmap is also uninitalized, we need
to get write access to the block group descriptor before we start
modifying the block group descriptor flags and updating the free block
count, etc.  Otherwise, there is the potential of a bad journal
checksum (if journal checksums are enabled), and of the file system
becoming inconsistent if we crash at exactly the wrong time.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
ext4: clarify error count warning messages

Make it clear that values printed are times, and that it is error
since last fsck. Also add note about fsck version required.

Signed-off-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Cc: stable@vger.kernel.org
ext4: clarify ext4_error message in ext4_mb_generate_buddy_error()

We are spending a lot of time explaining to users what this error
means.  Let's try to improve the message to avoid this problem.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
ext4: disable synchronous transaction batching if max_batch_time==0

The mount manpage says of the max_batch_time option,

	This optimization can be turned off entirely
	by setting max_batch_time to 0.

But the code doesn't do that.  So fix the code to do
that.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
ext4: revert commit which was causing fs corruption after journal replays

Commit 007649375f6af2 ("ext4: initialize multi-block allocator before
checking block descriptors") causes the block group descriptor's count
of the number of free blocks to become inconsistent with the number of
free blocks in the allocation bitmap.  This is a harmless form of fs
corruption, but it causes the kernel to potentially remount the file
system read-only, or to panic, depending on the file systems's error
behavior.

Thanks to Eric Whitney for his tireless work to reproduce and to find
the guilty commit.

Fixes: 007649375f6af2 ("ext4: initialize multi-block allocator before checking block descriptors"

Cc: stable@vger.kernel.org  # 3.15
Reported-by: David Jander <david@protonic.nl>
Reported-by: Matteo Croce <technoboy85@gmail.com>
Tested-by: Eric Whitney <enwlinux@gmail.com>
Suggested-by: Eric Whitney <enwlinux@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
ext4: fix a potential deadlock in __ext4_es_shrink()

This fixes the following lockdep complaint:

[ INFO: possible circular locking dependency detected ]
3.16.0-rc2-mm1+ #7 Tainted: G           O  
-------------------------------------------------------
kworker/u24:0/4356 is trying to acquire lock:
 (&(&sbi->s_es_lru_lock)->rlock){+.+.-.}, at: [<ffffffff81285fff>] __ext4_es_shrink+0x4f/0x2e0

but task is already holding lock:
 (&ei->i_es_lock){++++-.}, at: [<ffffffff81286961>] ext4_es_insert_extent+0x71/0x180

which lock already depends on the new lock.

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&ei->i_es_lock);
                               lock(&(&sbi->s_es_lru_lock)->rlock);
                               lock(&ei->i_es_lock);
  lock(&(&sbi->s_es_lru_lock)->rlock);

 *** DEADLOCK ***

6 locks held by kworker/u24:0/4356:
 #0:  ("writeback"){.+.+.+}, at: [<ffffffff81071d00>] process_one_work+0x180/0x560
 #1:  ((&(&wb->dwork)->work)){+.+.+.}, at: [<ffffffff81071d00>] process_one_work+0x180/0x560
 #2:  (&type->s_umount_key#22){++++++}, at: [<ffffffff811a9c74>] grab_super_passive+0x44/0x90
 #3:  (jbd2_handle){+.+...}, at: [<ffffffff812979f9>] start_this_handle+0x189/0x5f0
 #4:  (&ei->i_data_sem){++++..}, at: [<ffffffff81247062>] ext4_map_blocks+0x132/0x550
 #5:  (&ei->i_es_lock){++++-.}, at: [<ffffffff81286961>] ext4_es_insert_extent+0x71/0x180

stack backtrace:
CPU: 0 PID: 4356 Comm: kworker/u24:0 Tainted: G           O   3.16.0-rc2-mm1+ #7
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
Workqueue: writeback bdi_writeback_workfn (flush-253:0)
 ffffffff8213dce0 ffff880014b07538 ffffffff815df0bb 0000000000000007
 ffffffff8213e040 ffff880014b07588 ffffffff815db3dd ffff880014b07568
 ffff880014b07610 ffff88003b868930 ffff88003b868908 ffff88003b868930
Call Trace:
 [<ffffffff815df0bb>] dump_stack+0x4e/0x68
 [<ffffffff815db3dd>] print_circular_bug+0x1fb/0x20c
 [<ffffffff810a7a3e>] __lock_acquire+0x163e/0x1d00
 [<ffffffff815e89dc>] ? retint_restore_args+0xe/0xe
 [<ffffffff815ddc7b>] ? __slab_alloc+0x4a8/0x4ce
 [<ffffffff81285fff>] ? __ext4_es_shrink+0x4f/0x2e0
 [<ffffffff810a8707>] lock_acquire+0x87/0x120
 [<ffffffff81285fff>] ? __ext4_es_shrink+0x4f/0x2e0
 [<ffffffff8128592d>] ? ext4_es_free_extent+0x5d/0x70
 [<ffffffff815e6f09>] _raw_spin_lock+0x39/0x50
 [<ffffffff81285fff>] ? __ext4_es_shrink+0x4f/0x2e0
 [<ffffffff8119760b>] ? kmem_cache_alloc+0x18b/0x1a0
 [<ffffffff81285fff>] __ext4_es_shrink+0x4f/0x2e0
 [<ffffffff812869b8>] ext4_es_insert_extent+0xc8/0x180
 [<ffffffff812470f4>] ext4_map_blocks+0x1c4/0x550
 [<ffffffff8124c4c4>] ext4_writepages+0x6d4/0xd00
	...

Reported-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: Minchan Kim <minchan@kernel.org>
Cc: stable@vger.kernel.org
Cc: Zheng Liu <gnehzuil.liu@gmail.com>
ext4: fix potential null pointer dereference in ext4_free_inode

Fix potential null pointer dereferencing problem caused by e43bb4e612
("ext4: decrement free clusters/inodes counters when block group declared bad")

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Merge tag 'ext4_for_linus_stable' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4

Pull ext4 bugfixes from Ted Ts'o:
 "More bug fixes for ext4 -- most importantly, a fix for a bug
  introduced in 3.15 that can end up triggering a file system corruption
  error after a journal replay.

  It shouldn't lead to any actual data corruption, but it is scary and
  can force file systems to be remounted read-only, etc"

* tag 'ext4_for_linus_stable' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4:
  ext4: fix potential null pointer dereference in ext4_free_inode
  ext4: fix a potential deadlock in __ext4_es_shrink()
  ext4: revert commit which was causing fs corruption after journal replays
  ext4: disable synchronous transaction batching if max_batch_time==0
  ext4: clarify ext4_error message in ext4_mb_generate_buddy_error()
  ext4: clarify error count warning messages
  ext4: fix unjournalled bg descriptor while initializing inode bitmap