Due to several different off-by-one errors, or perhaps due to a late
change in design that wasn't fully reflected in the code that was
actually merged, there are several very strange constraints on how
fast-commit blocks are filled with tlv entries:

- tlvs must start at least 10 bytes before the end of the block, even
  though the minimum tlv length is 8.  Otherwise, the replay code will
  ignore them.  (BUG: ext4_fc_reserve_space() could violate this
  requirement if called with a len of blocksize - 9 or blocksize - 8.
  Fortunately, this doesn't seem to happen currently.)

- tlvs must end at least 1 byte before the end of the block.  Otherwise
  the replay code will consider them to be invalid.  This quirk
  contributed to a bug (fixed by an earlier commit) where uninitialized
  memory was being leaked to disk in the last byte of blocks.

Also, strangely these constraints don't apply to the replay code in
e2fsprogs, which will accept any tlvs in the blocks (with no bounds
checks at all, but that is a separate issue...).

Given that this all seems to be a bug, let's fix it by just filling
blocks with tlv entries in the natural way.

Note that old kernels will be unable to replay fast-commit journals
created by kernels that have this commit.

Fixes: aa75f4d3 ("ext4: main fast-commit commit path")
Cc: <stable@vger.kernel.org> # v5.10+
Signed-off-by: NEric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20221106224841.279231-7-ebiggers@kernel.orgSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

As is done elsewhere in the file, build the struct ext4_fc_tl on the
stack and memcpy() it into the buffer, rather than directly writing it
to a potentially-unaligned location in the buffer.

Fixes: aa75f4d3 ("ext4: main fast-commit commit path")
Cc: <stable@vger.kernel.org> # v5.10+
Signed-off-by: NEric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20221106224841.279231-6-ebiggers@kernel.orgSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

Validate the inode and filename lengths in fast-commit journal records
so that a malicious fast-commit journal cannot cause a crash by having
invalid values for these.  Also validate EXT4_FC_TAG_DEL_RANGE.

Fixes: aa75f4d3 ("ext4: main fast-commit commit path")
Cc: <stable@vger.kernel.org> # v5.10+
Signed-off-by: NEric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20221106224841.279231-5-ebiggers@kernel.orgSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

When space at the end of fast-commit journal blocks is unused, make sure
to zero it out so that uninitialized memory is not leaked to disk.

Fixes: aa75f4d3 ("ext4: main fast-commit commit path")
Cc: <stable@vger.kernel.org> # v5.10+
Signed-off-by: NEric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20221106224841.279231-4-ebiggers@kernel.orgSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

Commit a80f7fcf ("ext4: fixup ext4_fc_track_* functions' signature")
extended the scope of the transaction in ext4_unlink() too far, making
it include the call to ext4_find_entry().  However, ext4_find_entry()
can deadlock when called from within a transaction because it may need
to set up the directory's encryption key.

Fix this by restoring the transaction to its original scope.

Reported-by: syzbot+1a748d0007eeac3ab079@syzkaller.appspotmail.com
Fixes: a80f7fcf ("ext4: fixup ext4_fc_track_* functions' signature")
Cc: <stable@vger.kernel.org> # v5.10+
Signed-off-by: NEric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20221106224841.279231-3-ebiggers@kernel.orgSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

fast-commit of create, link, and unlink operations in encrypted
directories is completely broken because the unencrypted filenames are
being written to the fast-commit journal instead of the encrypted
filenames.  These operations can't be replayed, as encryption keys
aren't present at journal replay time.  It is also an information leak.

Until if/when we can get this working properly, make encrypted directory
operations ineligible for fast-commit.

Note that fast-commit operations on encrypted regular files continue to
be allowed, as they seem to work.

Fixes: aa75f4d3 ("ext4: main fast-commit commit path")
Cc: <stable@vger.kernel.org> # v5.10+
Signed-off-by: NEric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20221106224841.279231-2-ebiggers@kernel.orgSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

With the new fortify string system, rework the memcpy to avoid this
warning:

memcpy: detected field-spanning write (size 60) of single field "&raw_inode->i_generation" at fs/ext4/fast_commit.c:1551 (size 4)

Cc: stable@kernel.org
Fixes: 54d9469b ("fortify: Add run-time WARN for cross-field memcpy()")
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>

For scan loop must ensure that at least EXT4_FC_TAG_BASE_LEN space. If remain
space less than EXT4_FC_TAG_BASE_LEN which will lead to out of bound read
when mounting corrupt file system image.
ADD_RANGE/HEAD/TAIL is needed to add extra check when do journal scan, as this
three tags will read data during scan, tag length couldn't less than data length
which will read.

Cc: stable@kernel.org
Signed-off-by: NYe Bin <yebin10@huawei.com>
Link: https://lore.kernel.org/r/20220924075233.2315259-4-yebin10@huawei.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

Factor out ext4_fc_get_tl() to fill 'tl' with host byte order.
Signed-off-by: NYe Bin <yebin10@huawei.com>
Link: https://lore.kernel.org/r/20220924075233.2315259-3-yebin10@huawei.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

Introduce EXT4_FC_TAG_BASE_LEN helper for calculate length of
struct ext4_fc_tl.
Signed-off-by: NYe Bin <yebin10@huawei.com>
Link: https://lore.kernel.org/r/20220924075233.2315259-2-yebin10@huawei.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

Factor out ext4_free_ext_path() to free extent path. As after previous patch
'ext4_ext_drop_refs()' is only used in 'extents.c', so make it static.
Signed-off-by: NYe Bin <yebin10@huawei.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220924021211.3831551-3-yebin10@huawei.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

To avoid to 'state->fc_regions_size' mismatch with 'state->fc_regions'
when fail to reallocate 'fc_reqions',only update 'state->fc_regions_size'
after 'state->fc_regions' is allocated successfully.

Cc: stable@kernel.org
Signed-off-by: NYe Bin <yebin10@huawei.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220921064040.3693255-4-yebin10@huawei.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

As krealloc may return NULL, in this case 'state->fc_regions' may not be
freed by krealloc, but 'state->fc_regions' already set NULL. Then will
lead to 'state->fc_regions' memory leak.

Cc: stable@kernel.org
Signed-off-by: NYe Bin <yebin10@huawei.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220921064040.3693255-3-yebin10@huawei.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

As krealloc may return NULL, in this case 'state->fc_modified_inodes'
may not be freed by krealloc, but 'state->fc_modified_inodes' already
set NULL. Then will lead to 'state->fc_modified_inodes' memory leak.

Cc: stable@kernel.org
Signed-off-by: NYe Bin <yebin10@huawei.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220921064040.3693255-2-yebin10@huawei.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

If fastcommit is already disabled, there isn't need to mark inode ineligible.
So move 'ext4_fc_disabled()' judgement bofore 'ext4_should_journal_data(inode)'
judgement which can avoid to do meaningless judgement.
Signed-off-by: NYe Bin <yebin10@huawei.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220916083836.388347-3-yebin10@huawei.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

Factor out ext4_fc_disabled(). No functional change.
Signed-off-by: NYe Bin <yebin10@huawei.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220916083836.388347-2-yebin10@huawei.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

In 'ext4_fc_write_inode' function first call 'ext4_get_inode_loc' get 'iloc',
after use it miss release 'iloc.bh'.
So just release 'iloc.bh' before 'ext4_fc_write_inode' return.

Cc: stable@kernel.org
Signed-off-by: NYe Bin <yebin10@huawei.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220914100859.1415196-1-yebin10@huawei.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

We use jbd_debug() in some places in ext4. It seems a bit strange to use
jbd2 debugging output function for ext4 code. Also these days
ext4_debug() uses dynamic printk so each debug message can be enabled /
disabled on its own so the time when it made some sense to have these
combined (to allow easier common selecting of messages to report) has
passed. Just convert all jbd_debug() uses in ext4 to ext4_debug().
Signed-off-by: NJan Kara <jack@suse.cz>
Reviewed-by: NLukas Czerner <lczerner@redhat.com>
Link: https://lore.kernel.org/r/20220608112355.4397-1-jack@suse.czSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

Improve static type checking by using the new blk_opf_t type for
variables that represent request flags.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Baokun Li <libaokun1@huawei.com>
Cc: Ye Bin <yebin10@huawei.com>
Signed-off-by: NBart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20220714180729.1065367-52-bvanassche@acm.orgSigned-off-by: NJens Axboe <axboe@kernel.dk>

Both submit_bh() and ll_rw_block() accept a request operation type and
request flags as their first two arguments. Micro-optimize these two
functions by combining these first two arguments into a single argument.
This patch does not change the behavior of any of the modified code.

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jan Kara <jack@suse.cz>
Acked-by: Song Liu <song@kernel.org> (for the md changes)
Signed-off-by: NBart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20220714180729.1065367-48-bvanassche@acm.orgSigned-off-by: NJens Axboe <axboe@kernel.dk>

iput() has already handled null and non-null parameter, so it is no
need to use if().
Reported-by: NZeal Robot <zealci@zte.com.cn>
Signed-off-by: NLv Ruyi <lv.ruyi@zte.com.cn>
Link: https://lore.kernel.org/r/20220411032337.2517465-1-lv.ruyi@zte.com.cnSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

remove unnecessary void* type castings.
Signed-off-by: NYu Zhe <yuzhe@nfschina.com>
Link: https://lore.kernel.org/r/20220401081321.73735-1-yuzhe@nfschina.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

This adds commit_tid info in ext4_fc_commit_start/stop which is helpful
in debugging fast_commit issues.

For e.g. issues where due to jbd2 journal full commit, FC miss to commit
updates to a file.

Also improves TP_prink format string i.e. all ext4 and jbd2 trace events
starts with "dev MAjOR,MINOR". Let's follow the same convention while we
are still at it.
Signed-off-by: NRitesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Reviewed-by: NHarshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/ebcd6b9ab5b718db30f90854497886801ce38c63.1647057583.git.riteshh@linux.ibm.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

This adds commit_tid argument in ext4_fc_update_stats()
so that we can add this information too in jbd_debug logs.
This is also required in a later patch to pass the commit_tid info in
ext4_fc_commit_start/stop() trace events.
Signed-off-by: NRitesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Reviewed-by: NHarshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/dabda3f2919a60e01887e798bf5915216b451733.1647057583.git.riteshh@linux.ibm.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

This patch adds the transaction & inode tid info in trace events for
callers of ext4_fc_track_template(). This is helpful in debugging race
conditions where an inode could belong to two different transaction tids.
It also fixes the checkpatch warnings which says use tabs instead of
spaces.
Signed-off-by: NRitesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/c203c09dc11bb372803c430f621f25a4b8c2c8b4.1647057583.git.riteshh@linux.ibm.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

This adds a new trace event in ext4_fc_cleanup() which is helpful in debugging
some fast_commit issues.
Signed-off-by: NRitesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/794cdb1d5d3622f3f80d30c222ff6652ea68c375.1647057583.git.riteshh@linux.ibm.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

Currently ext4_fc_track_template() checks, whether the trace event
path belongs to replay or does sb has ineligible set, if yes it simply
returns. This patch pulls those checks before calling
ext4_fc_track_template() in the callers of ext4_fc_track_template().

[ Add checks to ext4_rename() which calls the __ext4_fc_track_*()
  functions directly. -- TYT ]
Signed-off-by: NRitesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/3cd025d9c490218a92e6d8fb30b6123e693373e3.1647057583.git.riteshh@linux.ibm.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

This just puts trace_ext4_fc_commit_start(sb) & ktime_get()
for measuring FC commit time, after the check of whether sb
supports JOURNAL_FAST_COMMIT or not.
Signed-off-by: NRitesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: NHarshad Shirwadkar <harshadshirwadkar@gmail.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/d53cf3e535924ec0a1eb41a560e96561b0727e7a.1647057583.git.riteshh@linux.ibm.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

Currently ext4_fc_commit_dentry_updates() is of quadratic time
complexity, which is causing performance bottlenecks with high
threads/file/dir count with fs_mark.

This patch makes commit dentry updates (and hence ext4_fc_commit()) path
to linear time complexity. Hence improves the performance of workloads
which does fsync on multiple threads/open files one-by-one.

Absolute numbers in avg file creates per sec (from fs_mark in 1K order)
=======================================================================
no.     Order   without-patch(K)   with-patch(K)   Diff(%)
1       1        16.90              17.51           +3.60
2       2,2      32.08              31.80           -0.87
3       3,3      53.97              55.01           +1.92
4       4,4      78.94              76.90           -2.58
5       5,5      95.82              95.37           -0.46
6       6,6      87.92              103.38          +17.58
7       6,10      0.73              126.13          +17178.08
8       6,14      2.33              143.19          +6045.49

workload type
==============
For e.g. 7th row order of 6,10 (2^6 == 64 && 2^10 == 1024)
echo /run/riteshh/mnt/{1..64} |sed -E 's/[[:space:]]+/ -d /g' \
  | xargs -I {} bash -c "sudo fs_mark -L 100 -D 1024 -n 1024 -s0 -S5 -d {}"

Perf profile
(w/o patches)
=============================
87.15%  [kernel]  [k] ext4_fc_commit           --> Heavy contention/bottleneck
 1.98%  [kernel]  [k] perf_event_interrupt
 0.96%  [kernel]  [k] power_pmu_enable
 0.91%  [kernel]  [k] update_sd_lb_stats.constprop.0
 0.67%  [kernel]  [k] ktime_get
Signed-off-by: NRitesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: NHarshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/930f35d4fd5f83e2673c868781d9ebf15e91bf4e.1645426817.git.riteshh@linux.ibm.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

Instead of open coding it, use in_range() function instead.
Signed-off-by: NRitesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/8e5526ef14150778871ac7c937c8993c6a09cd3e.1644992610.git.riteshh@linux.ibm.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

should not use fast commit log data directly, add le32_to_cpu().
Reported-by: Nkernel test robot <lkp@intel.com>
Fixes: 0b5b5a62 ("ext4: use ext4_ext_remove_space() for fast commit replay delete range")
Cc: stable@kernel.org
Signed-off-by: NXin Yin <yinxin.x@bytedance.com>
Reviewed-by: NRitesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/20220126063146.2302-1-yinxin.x@bytedance.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

Current code does not fully takes care of krealloc() error case, which
could lead to silent memory corruption or a kernel bug.  This patch
fixes that.

Also it cleans up some duplicated error handling logic from various
functions in fast_commit.c file.
Reported-by: Nluo penghao <luo.penghao@zte.com.cn>
Suggested-by: NLukas Czerner <lczerner@redhat.com>
Signed-off-by: NRitesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/62e8b6a1cce9359682051deb736a3c0953c9d1e9.1642416995.git.riteshh@linux.ibm.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

in the follow scenario:
1. jbd start transaction n
2. task A get new handle for transaction n+1
3. task A do some actions and add inode to FC_Q_MAIN fc_q
4. jbd complete transaction n and clear FC_Q_MAIN fc_q
5. task A call fsync

Fast commit will lost the file actions during a full commit.

we should also add updates to staging queue during a full commit.
and in ext4_fc_cleanup(), when reset a inode's fc track range, check
it's i_sync_tid, if it bigger than current transaction tid, do not
rest it, or we will lost the track range.

And EXT4_MF_FC_COMMITTING is not needed anymore, so drop it.
Signed-off-by: NXin Yin <yinxin.x@bytedance.com>
Link: https://lore.kernel.org/r/20220117093655.35160-3-yinxin.x@bytedance.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

For the follow scenario:
1. jbd start commit transaction n
2. task A get new handle for transaction n+1
3. task A do some ineligible actions and mark FC_INELIGIBLE
4. jbd complete transaction n and clean FC_INELIGIBLE
5. task A call fsync

In this case fast commit will not fallback to full commit and
transaction n+1 also not handled by jbd.

Make ext4_fc_mark_ineligible() also record transaction tid for
latest ineligible case, when call ext4_fc_cleanup() check
current transaction tid, if small than latest ineligible tid
do not clear the EXT4_MF_FC_INELIGIBLE.
Reported-by: Nkernel test robot <lkp@intel.com>
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Reported-by: NRitesh Harjani <riteshh@linux.ibm.com>
Suggested-by: NHarshad Shirwadkar <harshadshirwadkar@gmail.com>
Signed-off-by: NXin Yin <yinxin.x@bytedance.com>
Link: https://lore.kernel.org/r/20220117093655.35160-2-yinxin.x@bytedance.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

During fast commit replay procedure, we clear inode blocks bitmap in
ext4_ext_clear_bb(), this may cause ext4_mb_new_blocks_simple() allocate
blocks still in use.

Make ext4_fc_record_regions() also record physical disk regions used by
inodes during replay procedure. Then ext4_mb_new_blocks_simple() can
excludes these blocks in use.
Signed-off-by: NXin Yin <yinxin.x@bytedance.com>
Link: https://lore.kernel.org/r/20220110035141.1980-2-yinxin.x@bytedance.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

The local variable assignment at the end of the function is meaningless.

The clang_analyzer complains as follows:

fs/ext4/fast_commit.c:779:2 warning:

Value stored to 'dst' is never read
Reported-by: NZeal Robot <zealci@zte.com.cn>
Signed-off-by: Nluo penghao <luo.penghao@zte.com.cn>
Link: https://lore.kernel.org/r/20211104063406.2747-1-luo.penghao@zte.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

The kmemcache for ext4_fc_dentry_cachep remains registered after module
removal.

Destroy ext4_fc_dentry_cachep kmemcache on module removal.

Fixes: aa75f4d3 ("ext4: main fast-commit commit path")
Signed-off-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: NLukas Czerner <lczerner@redhat.com>
Reviewed-by: NHarshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20211110134640.lyku5vklvdndw6uk@linutronix.de
Link: https://lore.kernel.org/r/YbiK3JetFFl08bd7@linutronix.de
Link: https://lore.kernel.org/r/20211223164436.2628390-1-bigeasy@linutronix.deSigned-off-by: NTheodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

For now ,we use ext4_punch_hole() during fast commit replay delete range
procedure. But it will be affected by inode->i_size, which may not
correct during fast commit replay procedure. The following test will
failed.

-create & write foo (len 1000K)
-falloc FALLOC_FL_ZERO_RANGE foo (range 400K - 600K)
-create & fsync bar
-falloc FALLOC_FL_PUNCH_HOLE foo (range 300K-500K)
-fsync foo
-crash before a full commit

After the fast_commit reply procedure, the range 400K-500K will not be
removed. Because in this case, when calling ext4_punch_hole() the
inode->i_size is 0, and it just retruns with doing nothing.

Change to use ext4_ext_remove_space() instead of ext4_punch_hole()
to remove blocks of inode directly.
Signed-off-by: NXin Yin <yinxin.x@bytedance.com>
Reviewed-by: NHarshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20211223032337.5198-2-yinxin.x@bytedance.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

This series takes care of a couple of TODOs and adds new ones. Update
the TODOs section to reflect current state and future work that needs
to happen.
Signed-off-by: NHarshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20211223202140.2061101-5-harshads@google.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

Move fast commit stats updating logic to a separate function from
ext4_fc_commit(). This significantly improves readability of
ext4_fc_commit().
Signed-off-by: NHarshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20211223202140.2061101-4-harshads@google.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>