- 25 Jan, 2020 5 commits
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Dmitry Monakhov authored
Show pblock only if it has meaningful value. # before ext4:ext4_es_lookup_extent_exit: dev 253,0 ino 12 found 1 [1/4294967294) 576460752303423487 H ext4:ext4_es_lookup_extent_exit: dev 253,0 ino 12 found 1 [2/4294967293) 576460752303423487 HR # after ext4:ext4_es_lookup_extent_exit: dev 253,0 ino 12 found 1 [1/4294967294) 0 H ext4:ext4_es_lookup_extent_exit: dev 253,0 ino 12 found 1 [2/4294967293) 0 HR Signed-off-by:
Dmitry Monakhov <dmonakhov@gmail.com> Link: https://lore.kernel.org/r/20191114200147.1073-2-dmonakhov@gmail.comSigned-off-by:
Theodore Ts'o <tytso@mit.edu>
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Dmitry Monakhov authored
Trace's macro __print_flags() produce raw event's decraration w/o knowing actual flags value cat /sys/kernel/debug/tracing/events/ext4/ext4_ext_map_blocks_exit/format .. __print_flags(REC->mflags, "", { (1 << BH_New), For that reason we have to explicitly define it via special macro TRACE_DEFINE_ENUM() Also add missed EXTENT_STATUS_REFERENCED flag. #Before patch ext4:ext4_ext_map_blocks_exit: dev 253,0 ino 2 flags lblk 0 pblk 4177 len 1 mflags 0x20 ret 1 ext4:ext4_ext_map_blocks_exit: dev 253,0 ino 12 flags CREATE lblk 0 pblk 34304 len 1 mflags 0x60 ret 1 #With patch ext4:ext4_ext_map_blocks_exit: dev 253,0 ino 2 flags lblk 0 pblk 4177 len 1 mflags M ret 1 ext4:ext4_ext_map_blocks_exit: dev 253,0 ino 12 flags CREATE lblk 0 pblk 34816 len 1 mflags NM ret 1 Signed-off-by: -
Chengguang Xu authored
Setting softlimit larger than hardlimit seems meaningless for disk quota but currently it is allowed. In this case, there may be a bit of comfusion for users when they run df comamnd to directory which has project quota. For example, we set 20M softlimit and 10M hardlimit of block usage limit for project quota of test_dir(project id 123). [root@hades mnt_ext4]# repquota -P -a *** Report for project quotas on device /dev/loop0 Block grace time: 7days; Inode grace time: 7days Block limits File limits Project used soft hard grace used soft hard grace ---------------------------------------------------------------------- 0 -- 13 0 0 2 0 0 123 -- 10237 20480 10240 5 200 100 The result of df command as below: [root@hades mnt_ext4]# df -h test_dir Filesystem Size Used Avail Use% Mounted on /dev/loop0 20M 10M 10M 50% /home/cgxu/test/mnt_ext4 Even though it looks like there is another 10M free space to use, if we write new data to diretory test_dir(inherit project id), the write will fail with errno(-EDQUOT). After this patch, the df result looks like below. [root@hades mnt_ext4]# df -h test_dir Filesystem Size Used Avail Use% Mounted on /dev/loop0 10M 10M 3.0K 100% /home/cgxu/test/mnt_ext4 Signed-off-by:Chengguang Xu <cgxu519@mykernel.net> Reviewed-by:
Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20191016022501.760-1-cgxu519@mykernel.netSigned-off-by:
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Eric Biggers authored
Since ->d_compare() and ->d_hash() can be called in RCU-walk mode, ->d_parent and ->d_inode can be concurrently modified, and in particular, ->d_inode may be changed to NULL. For ext4_d_hash() this resulted in a reproducible NULL dereference if a lookup is done in a directory being deleted, e.g. with: int main() { if (fork()) { for (;;) { mkdir("subdir", 0700); rmdir("subdir"); } } else { for (;;) access("subdir/file", 0); } } ... or by running the 't_encrypted_d_revalidate' program from xfstests. Both repros work in any directory on a filesystem with the encoding feature, even if the directory doesn't actually have the casefold flag. I couldn't reproduce a crash in ext4_d_compare(), but it appears that a similar crash is possible there. Fix these bugs by reading ->d_parent and ->d_inode using READ_ONCE() and falling back to the case sensitive behavior if the inode is NULL. Reported-by:Al Viro <viro@zeniv.linux.org.uk> Fixes: b886ee3e ("ext4: Support case-insensitive file name lookups") Cc: <stable@vger.kernel.org> # v5.2+ Signed-off-by:
Eric Biggers <ebiggers@google.com> Link: https://lore.kernel.org/r/20200124041234.159740-1-ebiggers@kernel.orgSigned-off-by:
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Theodore Ts'o authored
This fixes the direct I/O versus writeback race which can reveal stale data, and it improves the tail latency of commits on slow devices. Link: https://lore.kernel.org/r/20200125022254.1101588-1-tytso@mit.eduSigned-off-by:
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- 23 Jan, 2020 1 commit
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Dmitry Monakhov authored
Extents are cached in read_extent_tree_block(); as a result, extents are not cached for inodes with depth == 0 when we try to find the extent using ext4_find_extent(). The result of the lookup is cached in ext4_map_blocks() but is only a subset of the extent on disk. As a result, the contents of extents status cache can get very badly fragmented for certain workloads, such as a random 4k read workload. File size of /mnt/test is 33554432 (8192 blocks of 4096 bytes) ext: logical_offset: physical_offset: length: expected: flags: 0: 0.. 8191: 40960.. 49151: 8192: last,eof $ perf record -e 'ext4:ext4_es_*' /root/bin/fio --name=t --direct=0 --rw=randread --bs=4k --filesize=32M --size=32M --filename=/mnt/test $ perf script | grep ext4_es_insert_extent | head -n 10 fio 131 [000] 13.975421: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [494/1) mapped 41454 status W fio 131 [000] 13.975939: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [6064/1) mapped 47024 status W fio 131 [000] 13.976467: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [6907/1) mapped 47867 status W fio 131 [000] 13.976937: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [3850/1) mapped 44810 status W fio 131 [000] 13.977440: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [3292/1) mapped 44252 status W fio 131 [000] 13.977931: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [6882/1) mapped 47842 status W fio 131 [000] 13.978376: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [3117/1) mapped 44077 status W fio 131 [000] 13.978957: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [2896/1) mapped 43856 status W fio 131 [000] 13.979474: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [7479/1) mapped 48439 status W Fix this by caching the extents for inodes with depth == 0 in ext4_find_extent(). [ Renamed ext4_es_cache_extents() to ext4_cache_extents() since this newly added function is not in extents_cache.c, and to avoid potential visual confusion with ext4_es_cache_extent(). -TYT ] Signed-off-by:
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- 17 Jan, 2020 27 commits
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Kai Li authored
If the journal is dirty when the filesystem is mounted, jbd2 will replay the journal but the journal superblock will not be updated by journal_reset() because JBD2_ABORT flag is still set (it was set in journal_init_common()). This is problematic because when a new transaction is then committed, it will be recorded in block 1 (journal->j_tail was set to 1 in journal_reset()). If unclean shutdown happens again before the journal superblock is updated, the new recorded transaction will not be replayed during the next mount (because of stale sb->s_start and sb->s_sequence values) which can lead to filesystem corruption. Fixes: 85e0c4e8 ("jbd2: if the journal is aborted then don't allow update of the log tail") Signed-off-by:
Kai Li <li.kai4@h3c.com> Link: https://lore.kernel.org/r/20200111022542.5008-1-li.kai4@h3c.comSigned-off-by:
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Theodore Ts'o authored
As Jan pointed out[1], as of commit 81378da6 ("jbd2: mark the transaction context with the scope GFP_NOFS context") we use memalloc_nofs_{save,restore}() while a jbd2 handle is active. So ext4_kvmalloc() so we can call allocate using GFP_NOFS is no longer necessary. [1] https://lore.kernel.org/r/20200109100007.GC27035@quack2.suse.czSigned-off-by:
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Martijn Coenen authored
These are backed by 'struct fsxattr' which has the same size on all architectures. Signed-off-by:
Martijn Coenen <maco@android.com> Link: https://lore.kernel.org/r/20191227134639.35869-1-maco@android.comSigned-off-by:
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Ritesh Harjani authored
Remove unused macro MPAGE_DA_EXTENT_TAIL which is no more used after below commit 4e7ea81d ("ext4: restructure writeback path") Signed-off-by:
Ritesh Harjani <riteshh@linux.ibm.com> Reviewed-by:
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Eric Biggers authored
For clarity, add braces to the loop in ext4_ext_drop_refs(). Signed-off-by:
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Eric Biggers authored
Clean up some code that was using 2-character indents. Signed-off-by:
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Eric Biggers authored
Support for unwritten extents was added to ext4 a long time ago, so remove a misleading comment that says they're a future feature. Signed-off-by:
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Eric Biggers authored
Don't mention the nonexistent return value, and mention both types of merges that are attempted. Signed-off-by:
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Eric Biggers authored
Make the following functions static since they're only used in extents.c: __ext4_ext_dirty() ext4_can_extents_be_merged() ext4_collapse_range() ext4_insert_range() Also remove the prototype for ext4_ext_writepage_trans_blocks(), as this function is not defined anywhere. Signed-off-by:
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Eric Biggers authored
ext4_fallocate() is only used in the file_operations for regular files. Also, the VFS only allows fallocate() on regular files and block devices, but block devices always use blkdev_fallocate(). For both of these reasons, S_ISREG() is always true in ext4_fallocate(). Therefore the S_ISREG() checks in ext4_zero_range(), ext4_collapse_range(), ext4_insert_range(), and ext4_punch_hole() are redundant. Remove them. Signed-off-by:
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Eric Biggers authored
- Fix some comments. - Consistently access i_size directly rather than using i_size_read(), since in all relevant cases we're under inode_lock(). - Simplify the alignment checks by using the IS_ALIGNED() macro. - In ext4_insert_range(), do the check against s_maxbytes in a way that is safe against signed overflow. (This doesn't currently matter for ext4 due to ext4's limited max file size, but this is something other filesystems have gotten wrong. We might as well do it safely.) Signed-off-by:
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Eric Biggers authored
Remove the ext4_ind_calc_metadata_amount() and ext4_ext_calc_metadata_amount() functions, which have been unused since commit 71d4f7d0 ("ext4: remove metadata reservation checks"). Also remove the i_da_metadata_calc_last_lblock and i_da_metadata_calc_len fields from struct ext4_inode_info, as these were only used by these removed functions. Signed-off-by:
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Eric Biggers authored
Since allocating an object from a mempool never fails when __GFP_DIRECT_RECLAIM (which is included in GFP_NOFS) is set, the check for failure to allocate a bio_post_read_ctx is unnecessary. Remove it. Also remove the redundant assignment to ->bi_private. Signed-off-by:
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Eric Biggers authored
Without any form of coordination, any case where multiple allocations from the same mempool are needed at a time to make forward progress can deadlock under memory pressure. This is the case for struct bio_post_read_ctx, as one can be allocated to decrypt a Merkle tree page during fsverity_verify_bio(), which itself is running from a post-read callback for a data bio which has its own struct bio_post_read_ctx. Fix this by freeing the first bio_post_read_ctx before calling fsverity_verify_bio(). This works because verity (if enabled) is always the last post-read step. This deadlock can be reproduced by trying to read from an encrypted verity file after reducing NUM_PREALLOC_POST_READ_CTXS to 1 and patching mempool_alloc() to pretend that pool->alloc() always fails. Note that since NUM_PREALLOC_POST_READ_CTXS is actually 128, to actually hit this bug in practice would require reading from lots of encrypted verity files at the same time. But it's theoretically possible, as N available objects isn't enough to guarantee forward progress when > N/2 threads each need 2 objects at a time. Fixes: 22cfe4b4 ("ext4: add fs-verity read support") Signed-off-by:
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Eric Biggers authored
ext4_writepages() on an encrypted file has to encrypt the data, but it can't modify the pagecache pages in-place, so it encrypts the data into bounce pages and writes those instead. All bounce pages are allocated from a mempool using GFP_NOFS. This is not correct use of a mempool, and it can deadlock. This is because GFP_NOFS includes __GFP_DIRECT_RECLAIM, which enables the "never fail" mode for mempool_alloc() where a failed allocation will fall back to waiting for one of the preallocated elements in the pool. But since this mode is used for all a bio's pages and not just the first, it can deadlock waiting for pages already in the bio to be freed. This deadlock can be reproduced by patching mempool_alloc() to pretend that pool->alloc() always fails (so that it always falls back to the preallocations), and then creating an encrypted file of size > 128 KiB. Fix it by only using GFP_NOFS for the first page in the bio. For subsequent pages just use GFP_NOWAIT, and if any of those fail, just submit the bio and start a new one. This will need to be fixed in f2fs too, but that's less straightforward. Fixes: c9af28fd ("ext4 crypto: don't let data integrity writebacks fail with ENOMEM") Cc: stable@vger.kernel.org Signed-off-by:
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Naoto Kobayashi authored
Since we're not using ext4_kvzalloc(), delete this function. Signed-off-by:
Naoto Kobayashi <naoto.kobayashi4c@gmail.com> Link: https://lore.kernel.org/r/20191227080523.31808-2-naoto.kobayashi4c@gmail.comSigned-off-by:
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Eric Biggers authored
For encrypted files, commit 36086d43 ("ext4 crypto: fix bugs in ext4_encrypted_zeroout()") disabled the optimization where when a write occurs to the middle of an unwritten extent, the head and/or tail of the extent (when they aren't too large) are zeroed out, turned into an initialized extent, and merged with the part being written to. This optimization helps prevent fragmentation of the extent tree. However, disabling this optimization also made fscrypt_zeroout_range() nearly impossible to test, as now it's only reachable via the very rare case in ext4_split_extent_at() where allocating a new extent tree block fails due to ENOSPC. 'gce-xfstests -c ext4/encrypt -g auto' doesn't even hit this at all. It's preferable to avoid really rare cases that are hard to test. That commit also cited data corruption in xfstest generic/127 as a reason to disable the extent zeroout optimization, but that's no longer reproducible anymore. It also cited fscrypt_zeroout_range() having poor performance, but I've written a patch to fix that. Therefore, re-enable the extent zeroout optimization on encrypted files. Signed-off-by:
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Eric Biggers authored
fscrypt_zeroout_range() is only for encrypted regular files, not for encrypted directories or symlinks. Fortunately, currently it seems it's never called on non-regular files. But to be safe ext4 should explicitly check S_ISREG() before calling it. Signed-off-by:
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Eric Biggers authored
When ext4 encryption support was first added, ZERO_RANGE was disallowed, supposedly because test failures (e.g. ext4/001) were seen when enabling it, and at the time there wasn't enough time/interest to debug it. However, there's actually no reason why ZERO_RANGE can't work on encrypted files. And it fact it *does* work now. Whole blocks in the zeroed range are converted to unwritten extents, as usual; encryption makes no difference for that part. Partial blocks are zeroed in the pagecache and then ->writepages() encrypts those blocks as usual. ext4_block_zero_page_range() handles reading and decrypting the block if needed before actually doing the pagecache write. Also, f2fs has always supported ZERO_RANGE on encrypted files. As far as I can tell, the reason that ext4/001 was failing in v4.1 was actually because of one of the bugs fixed by commit 36086d43 ("ext4 crypto: fix bugs in ext4_encrypted_zeroout()"). The bug made ext4_encrypted_zeroout() always return a positive value, which caused unwritten extents in encrypted files to sometimes not be marked as initialized after being written to. This bug was not actually in ZERO_RANGE; it just happened to trigger during the extents manipulation done in ext4/001 (and probably other tests too). So, let's enable ZERO_RANGE on encrypted files on ext4. Tested with: gce-xfstests -c ext4/encrypt -g auto gce-xfstests -c ext4/encrypt_1k -g auto Got the same set of test failures both with and without this patch. But with this patch 6 fewer tests are skipped: ext4/001, generic/008, generic/009, generic/033, generic/096, and generic/511. Signed-off-by:
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Eric Biggers authored
fscrypt_decrypt_pagecache_blocks() can fail, because it uses skcipher_request_alloc(), which uses kmalloc(), which can fail; and also because it calls crypto_skcipher_decrypt(), which can fail depending on the driver that actually implements the crypto. Therefore it's not appropriate to WARN on decryption error in __ext4_block_zero_page_range(). Remove the WARN and just handle the error instead. Signed-off-by:
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Eric Biggers authored
Mention encryption and verity in the ext4 features list. Signed-off-by:
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Eric Biggers authored
Since EXT3_FS already selects EXT4_FS, there's no reason for it to redundantly select all the selections of EXT4_FS -- notwithstanding the comments that claim otherwise. Remove these redundant selections to avoid confusion. Signed-off-by:
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zhengbin authored
Fixes coccicheck warning: fs/ext4/extents.c:5271:6-12: WARNING: Assignment of 0/1 to bool variable fs/ext4/extents.c:5287:4-10: WARNING: Assignment of 0/1 to bool variable Reported-by:
Hulk Robot <hulkci@huawei.com> Signed-off-by:
zhengbin <zhengbin13@huawei.com> Reviewed-by:
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Eric Biggers authored
Determining an inode's journaling mode has gotten more complicated over time. Move ext4_inode_journal_mode() from an inline function into ext4_jbd2.c to reduce the compiled code size. Signed-off-by:
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Eric Biggers authored
The ifdefs for CONFIG_FS_ENCRYPTION in htree_dirblock_to_tree() are unnecessary, as the called functions are already stubbed out when !CONFIG_FS_ENCRYPTION. Remove them. Signed-off-by:
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Chengguang Xu authored
We have allocated memory using kzalloc() so don't have to set 0 again in last byte. Signed-off-by:
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Theodore Ts'o authored
Linus observed that an allmodconfig build which does a lot of stat(2) calls that ext4_getattr() was a noticeable (1%) amount of CPU time, due to the cache line for i_extra_isize getting pulled in. Since the normal stat system call doesn't return btime, it's a complete waste. So only calculate btime when it is explicitly requested. [ Fixed to check against request_mask instead of query_flags. ] Link: https://lore.kernel.org/r/CAHk-=wivmk_j6KbTX+Er64mLrG8abXZo0M10PNdAnHc8fWXfsQ@mail.gmail.comReported-by:
Linus Torvalds <torvalds@linux-foundation.org> Reviewed-by:
Andreas Dilger <adilger@dilger.ca> Signed-off-by:
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- 26 Dec, 2019 5 commits
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Jan Kara authored
Currently we start transaction for mapping every extent for writing using direct IO. This is unnecessary when we know we are overwriting already allocated blocks and the overhead of starting a transaction can be significant especially for multithreaded workloads doing small writes. Use iomap operations that avoid starting a transaction for direct IO overwrites. This improves throughput of 4k random writes - fio jobfile: [global] rw=randrw norandommap=1 invalidate=0 bs=4k numjobs=16 time_based=1 ramp_time=30 runtime=120 group_reporting=1 ioengine=psync direct=1 size=16G filename=file1.0.0:file1.0.1:file1.0.2:file1.0.3:file1.0.4:file1.0.5:file1.0.6:file1.0.7:file1.0.8:file1.0.9:file1.0.10:file1.0.11:file1.0.12:file1.0.13:file1.0.14:file1.0.15:file1.0.16:file1.0.17:file1.0.18:file1.0.19:file1.0.20:file1.0.21:file1.0.22:file1.0.23:file1.0.24:file1.0.25:file1.0.26:file1.0.27:file1.0.28:file1.0.29:file1.0.30:file1.0.31 file_service_type=random nrfiles=32 from 3018MB/s to 4059MB/s in my test VM running test against simulated pmem device (note that before iomap conversion, this workload was able to achieve 3708MB/s because old direct IO path avoided transaction start for overwrites as well). For dax, the win is even larger improving throughput from 3042MB/s to 4311MB/s. Reported-by:
Dan Williams <dan.j.williams@intel.com> Signed-off-by:
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Theodore Ts'o authored
Make {first,last}_error_{ino,block,line,func,errcode} available via sysfs. Also add a missing newline for {first,last}_error_time. Signed-off-by: -
Theodore Ts'o authored
This allows us to test various error handling code paths Link: https://lore.kernel.org/r/20191209012317.59398-1-tytso@mit.eduSigned-off-by:
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Theodore Ts'o authored
This allows the cause of an ext4_error() report to be categorized based on whether it was triggered due to an I/O error, or an memory allocation error, or other possible causes. Most errors are caused by a detected file system inconsistency, so the default code stored in the superblock will be EXT4_ERR_EFSCORRUPTED. Link: https://lore.kernel.org/r/20191204032335.7683-1-tytso@mit.eduSigned-off-by:
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Theodore Ts'o authored
These are ilock patches which helps improve the current inode lock scalabiliy problem in ext4 DIO mixed read/write workload case. The problem was first reported by Joseph [1]. This should help improve mixed read/write workload cases for databases which use directIO. These patches are based upon upstream discussion with Jan Kara & Joseph [2]. The problem really is that in case of DIO overwrites, we start with a exclusive lock and then downgrade it later to shared lock. This causes a scalability problem in case of mixed DIO read/write workload case. i.e. if we have any ongoing DIO reads and then comes a DIO writes, (since writes starts with excl. inode lock) then it has to wait until the shared lock is released (which only happens when DIO read is completed). Same is true for vice versa as well. The same can be easily observed with perf-tools trace analysis [3]. For more details, including performance numbers, please see [4]. [1] https://lore.kernel.org/linux-ext4/1566871552-60946-4-git-send-email-joseph.qi@linux.alibaba.com/ [2] https://lore.kernel.org/linux-ext4/20190910215720.GA7561@quack2.suse.cz/ [3] https://raw.githubusercontent.com/riteshharjani/LinuxStudy/master/ext4/perf.report [4] https://lore.kernel.org/r/20191212055557.11151-1-riteshh@linux.ibm.com
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- 23 Dec, 2019 2 commits
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Ritesh Harjani authored
We were using shared locking only in case of dioread_nolock mount option in case of DIO overwrites. This mount condition is not needed anymore with current code, since:- 1. No race between buffered writes & DIO overwrites. Since buffIO writes takes exclusive lock & DIO overwrites will take shared locking. Also DIO path will make sure to flush and wait for any dirty page cache data. 2. No race between buffered reads & DIO overwrites, since there is no block allocation that is possible with DIO overwrites. So no stale data exposure should happen. Same is the case between DIO reads & DIO overwrites. 3. Also other paths like truncate is protected, since we wait there for any DIO in flight to be over. Reviewed-by:
Joseph Qi <joseph.qi@linux.alibaba.com> Signed-off-by:
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Ritesh Harjani authored
Earlier there was no shared lock in DIO read path. But this patch (16c54688: ext4: Allow parallel DIO reads) simplified some of the locking mechanism while still allowing for parallel DIO reads by adding shared lock in inode DIO read path. But this created problem with mixed read/write workload. It is due to the fact that in DIO path, we first start with exclusive lock and only when we determine that it is a ovewrite IO, we downgrade the lock. This causes the problem, since we still have shared locking in DIO reads. So, this patch tries to fix this issue by starting with shared lock and then switching to exclusive lock only when required based on ext4_dio_write_checks(). Other than that, it also simplifies below cases:- 1. Simplified ext4_unaligned_aio API to ext4_unaligned_io. Previous API was abused in the sense that it was not really checking for AIO anywhere also it used to check for extending writes. So this API was renamed and simplified to ext4_unaligned_io() which actully only checks if the IO is really unaligned. Now, in case of unaligned direct IO, iomap_dio_rw needs to do zeroing of partial block and that will require serialization against other direct IOs in the same block. So we take a exclusive inode lock for any unaligned DIO. In case of AIO we also need to wait for any outstanding IOs to complete so that conversion from unwritten to written is completed before anyone try to map the overlapping block. Hence we take exclusive inode lock and also wait for inode_dio_wait() for unaligned DIO case. Please note since we are anyway taking an exclusive lock in unaligned IO, inode_dio_wait() becomes a no-op in case of non-AIO DIO. 2. Added ext4_extending_io(). This checks if the IO is extending the file. 3. Added ext4_dio_write_checks(). In this we start with shared inode lock and only switch to exclusive lock if required. So in most cases with aligned, non-extending, dioread_nolock & overwrites, it tries to write with a shared lock. If not, then we restart the operation in ext4_dio_write_checks(), after acquiring exclusive lock. Reviewed-by:
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