- 08 Dec, 2020 40 commits
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Nikolay Borisov authored
Use only a single 'ret' to control whether we should abort the transaction or not. That's fine, because if we abort a transaction then btrfs_end_transaction will return the same value as passed to btrfs_abort_transaction. No semantic changes. Signed-off-by:
Nikolay Borisov <nborisov@suse.com> Reviewed-by:
David Sterba <dsterba@suse.com> Signed-off-by:
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Filipe Manana authored
When we are attempting to start writeback for an existing extent in NOCOW mode, at run_delalloc_nocow(), we must check if the extent is shared, and if it is, fallback to a COW write. However we do such check while still holding a read lock on the leaf that contains the file extent item, and that check, the call to btrfs_cross_ref_exist(), can take some time because: 1) It needs to do a search on the extent tree, which obviously takes some time, specially if delayed references are being run at the moment, as we can block when trying to lock currently write locked btree nodes; 2) It needs to check the delayed references for any existing reference for our data extent, this requires acquiring the delayed references' spinlock and maybe block on the mutex of a delayed reference head in the case where there is a delayed reference for our data extent, in the worst case it makes us release the path on the extent tree and retry the whole process again (going back to step 1). There are other operations we do while holding the leaf locked that can take some significant time as well (specially all together): * btrfs_extent_readonly() - to check if the block group containing the extent is currently in RO mode. This requires taking a spinlock and searching for the block group in a rbtree that can be big on large filesystems; * csum_exist_in_range() - to search if there are any checksums in the csum tree for the extent. Like before, this can take some time if we are in a filesystem that has both COW and NOCOW files, in which case the csum tree is not empty; * btrfs_inc_nocow_writers() - increment the number of nocow writers in the block group that contains the data extent. Needs to acquire a spinlock and search for the block group in a rbtree that can be big on large filesystems. So just unlock the leaf (release the path) before doing all those checks, since we do not need it anymore. In case we can not do a NOCOW write for the extent, due to any of those checks failing, and the writeback range goes beyond that extents' length, we will do another btree search for the next file extent item. The following script that calls dbench was used to measure the impact of this change on a VM with 8 CPUs, 16Gb of ram, using a raw NVMe device directly (no intermediary filesystem on the host) and using a non-debug kernel (default configuration on Debian): $ cat test-dbench.sh #!/bin/bash DEV=/dev/sdk MNT=/mnt/sdk MOUNT_OPTIONS="-o ssd -o nodatacow" MKFS_OPTIONS="-m single -d single" mkfs.btrfs -f $MKFS_OPTIONS $DEV mount $MOUNT_OPTIONS $DEV $MNT dbench -D $MNT -t 300 64 umount $MNT Before this change: Operation Count AvgLat MaxLat ---------------------------------------- NTCreateX 9326331 0.317 399.957 Close 6851198 0.002 6.402 Rename 394894 2.621 402.819 Unlink 1883131 0.931 398.082 Deltree 256 19.160 303.580 Mkdir 128 0.003 0.016 Qpathinfo 8452314 0.068 116.133 Qfileinfo 1481921 0.001 5.081 Qfsinfo 1549963 0.002 4.444 Sfileinfo 759679 0.084 17.079 Find 3268168 0.396 118.196 WriteX 4653310 0.056 110.993 ReadX 14618818 0.005 23.314 LockX 30364 0.003 0.497 UnlockX 30364 0.002 1.720 Flush 653619 16.954 569.299 Throughput 966.651 MB/sec 64 clients 64 procs max_latency=569.377 ms After this change: Operation Count AvgLat MaxLat ---------------------------------------- NTCreateX 9710433 0.302 232.449 Close 7132948 0.002 11.496 Rename 411144 2.452 131.805 Unlink 1960961 0.893 230.383 Deltree 256 14.858 198.646 Mkdir 128 0.002 0.005 Qpathinfo 8800890 0.066 111.588 Qfileinfo 1542556 0.001 3.852 Qfsinfo 1613835 0.002 5.483 Sfileinfo 790871 0.081 19.492 Find 3402743 0.386 120.185 WriteX 4842918 0.054 179.312 ReadX 15220407 0.005 32.435 LockX 31612 0.003 1.533 UnlockX 31612 0.002 1.047 Flush 680567 16.320 463.323 Throughput 1016.59 MB/sec 64 clients 64 procs max_latency=463.327 ms +5.0% throughput, -20.5% max latency Also, the following test using fio was run: $ cat test-fio.sh #!/bin/bash DEV=/dev/sdk MNT=/mnt/sdk MOUNT_OPTIONS="-o ssd -o nodatacow" MKFS_OPTIONS="-d single -m single" if [ $# -ne 4 ]; then echo "Use $0 NUM_JOBS FILE_SIZE FSYNC_FREQ BLOCK_SIZE" exit 1 fi NUM_JOBS=$1 FILE_SIZE=$2 FSYNC_FREQ=$3 BLOCK_SIZE=$4 cat <<EOF > /tmp/fio-job.ini [writers] rw=randwrite fsync=$FSYNC_FREQ fallocate=none group_reporting=1 direct=0 bs=$BLOCK_SIZE ioengine=sync size=$FILE_SIZE directory=$MNT numjobs=$NUM_JOBS EOF echo echo "Using fio config:" echo cat /tmp/fio-job.ini echo echo "mount options: $MOUNT_OPTIONS" echo mkfs.btrfs -f $MKFS_OPTIONS $DEV > /dev/null mount $MOUNT_OPTIONS $DEV $MNT echo "Creating nodatacow files before fio runs..." for ((i = 0; i < $NUM_JOBS; i++)); do xfs_io -f -c "pwrite -b 128M 0 $FILE_SIZE" "$MNT/writers.$i.0" done sync fio /tmp/fio-job.ini umount $MNT Before this change: $ ./test-fio.sh 16 512M 2 4K (...) WRITE: bw=28.3MiB/s (29.6MB/s), 28.3MiB/s-28.3MiB/s (29.6MB/s-29.6MB/s), io=8192MiB (8590MB), run=289800-289800msec After this change: $ ./test-fio.sh 16 512M 2 4K (...) WRITE: bw=31.2MiB/s (32.7MB/s), 31.2MiB/s-31.2MiB/s (32.7MB/s-32.7MB/s), io=8192MiB (8590MB), run=262845-262845msec +9.7% throughput, -9.8% runtime Signed-off-by:Filipe Manana <fdmanana@suse.com> Reviewed-by:
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David Sterba authored
The tree checker is called many times as it verifies metadata at read/write time. The checks follow a simple pattern: if (error_condition) { report_error(); return -EUCLEAN; } All the error reporting functions are annotated as __cold that is supposed to hint the compiler to move the statement block out of the hot path. This does not seem to happen that often. As the error condition is expected to be false almost always, we can annotate it with 'unlikely' as this satisfies one of the few use cases for the annotation. The expected outcome is a stronger hint to compiler to reorder the checks test jump to exit test jump to exit ... which can be observed in asm of eg. check_dir_item, btrfs_check_chunk_valid, check_root_item or check_leaf. There's a measurable run time improvement reported by Josef, the testing workload went from 655 MiB/s to 677 MiB/s, which is about +3%. There should be no functional changes but some of the conditions have been rewritten to produce more readable result, some lines are longer than 80, for the sake of readability. Signed-off-by: -
David Sterba authored
Without a NULL fs_info the helpers will print something like BTRFS error (device <unknown>): ... This can happen in contexts where fs_info is not available at all or it's potentially unsafe due to object lifetime. The <unknown> stub does not bring much information and with the prefix makes the message unnecessarily longer. Remove it for the NULL fs_info case. BTRFS error: ... Callers can add the device information to the message itself if needed. Reviewed-by:
Anand Jain <anand.jain@oracle.com> Signed-off-by:
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Qu Wenruo authored
In alloc_extent_buffer(), after we got a page from btree inode, we check if that page has private pointer attached. If attached, we check if the existing extent buffer has proper refs. If not (the eb is being freed), we will detach that private eb pointer. The point here is, we are detaching that eb pointer by calling: - ClearPagePrivate() - put_page() The put_page() here is especially confusing, as it's decreasing the ref from attach_page_private(). Without knowing that, it looks like the put_page() is for the find_or_create_page() call, confusing the reader. Since we're always modifying page private with attach_page_private() and detach_page_private(), the only open-coded detach_page_private() here is really confusing. Fix it by calling detach_page_private(). Reviewed-by:
Johannes Thumshirn <johannes.thumshirn@wdc.com> Signed-off-by:
Qu Wenruo <wqu@suse.com> Reviewed-by:
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Qu Wenruo authored
In btrfs_lookup_bio_sums() if the bio is pretty large, we want to start readahead in the csum tree. However the threshold is an immediate number, (PAGE_SIZE * 8), from the initial btrfs merge. The meaning of the value is pretty hard to guess, especially when the immediate number is from the times when 4K sectorsize was the default and only CRC32C was supported. For the most common btrfs setup, CRC32 csum and 4K sectorsize, it means just 32K read would kick readahead, while the csum itself is only 32 bytes in size. Now let's be more reasonable by taking both csum size and node size into consideration. If the csum size for the bio is larger than one leaf, then we kick the readahead. This means for current default btrfs, the threshold will be 16M. This change should not change performance observably, thus this is mostly a readability enhancement. Reviewed-by:
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Qu Wenruo authored
extent_invalidatepage() will try to clear all possible bits since it's calling clear_extent_bit() with delete == 1. This is currently fine, since for btree io tree, it only utilizes EXTENT_LOCK bit. But this could be a problem for later subpage support, which will utilize extra io tree bit to represent additional info. This patch will just convert that clear_extent_bit() to unlock_extent_cached(). For current code since only EXTENT_LOCKED bit is utilized, this doesn't change the behavior, but provides a much cleaner basis for incoming subpage support. Reviewed-by:
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Qu Wenruo authored
Parameter @phy_offset is the offset against the bio->bi_iter.bi_sector. @phy_offset is mostly for data io to lookup the csum in btrfs_io_bio. But for metadata, it's completely useless as metadata stores their own csum in its header, so we can remove it. Note: parameters @start and @end, they are not utilized at all for current sectorsize == PAGE_SIZE case, as we can grab eb directly from page. But those two parameters are very important for later subpage support, thus @start/@len are not touched here. Reviewed-by:
Josef Bacik <josef@toxicpanda.com> Reviewed-by:
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Qu Wenruo authored
That anonymous structure serve no special purpose, just replace it with regular members. Signed-off-by:
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Qu Wenruo authored
Currently the type is unsigned int which could change its width depending on the architecture. We need up to 32 bits so make it explicit. Reviewed-by:
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Qu Wenruo authored
Introduce a new helper to handle update page status in end_bio_extent_readpage(). This will be later used for subpage support where the page status update can be more complex than now. Signed-off-by:
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Qu Wenruo authored
In end_bio_extent_readpage() we had a strange dance around extent_start/extent_len. Hidden behind the strange dance is, it's just calling endio_readpage_release_extent() on each bvec range. Here is an example to explain the original work flow: Bio is for inode 257, containing 2 pages, for range [1M, 1M+8K) end_bio_extent_extent_readpage() entered |- extent_start = 0; |- extent_end = 0; |- bio_for_each_segment_all() { | |- /* Got the 1st bvec */ | |- start = SZ_1M; | |- end = SZ_1M + SZ_4K - 1; | |- update = 1; | |- if (extent_len == 0) { | | |- extent_start = start; /* SZ_1M */ | | |- extent_len = end + 1 - start; /* SZ_1M */ | | } | | | |- /* Got the 2nd bvec */ | |- start = SZ_1M + 4K; | |- end = SZ_1M + 4K - 1; | |- update = 1; | |- if (extent_start + extent_len == start) { | | |- extent_len += end + 1 - start; /* SZ_8K */ | | } | } /* All bio vec iterated */ | |- if (extent_len) { |- endio_readpage_release_extent(tree, extent_start, extent_len, update); /* extent_start == SZ_1M, extent_len == SZ_8K, uptodate = 1 */ As the above flow shows, the existing code in end_bio_extent_readpage() is accumulates extent_start/extent_len, and when the contiguous range stops, calls endio_readpage_release_extent() for the range. However current behavior has something not really considered: - The inode can change For bio, its pages don't need to have contiguous page_offset. This means, even pages from different inodes can be packed into one bio. - bvec cross page boundary There is a feature called multi-page bvec, where bvec->bv_len can go beyond bvec->bv_page boundary. - Poor readability This patch will address the problem: - Introduce a proper structure, processed_extent, to record processed extent range - Integrate inode/start/end/uptodate check into endio_readpage_release_extent() - Add more comment on each step. This should greatly improve the readability, now in end_bio_extent_readpage() there are only two endio_readpage_release_extent() calls. - Add inode check for contiguity Now we also ensure the inode is the same one before checking if the range is contiguous. Reviewed-by: -
Qu Wenruo authored
In extent-io-test, there are two invalid tests: - Invalid nodesize for test_eb_bitmaps() Instead of the sectorsize and nodesize combination passed in, we're always using hand-crafted nodesize, e.g: len = (sectorsize < BTRFS_MAX_METADATA_BLOCKSIZE) ? sectorsize * 4 : sectorsize; In above case, if we have 32K page size, then we will get a length of 128K, which is beyond max node size, and obviously invalid. The common page size goes up to 64K so we haven't hit that - Invalid extent buffer bytenr For 64K page size, the only combination we're going to test is sectorsize = nodesize = 64K. However, in that case we will try to test an eb which bytenr is not sectorsize aligned: /* Do it over again with an extent buffer which isn't page-aligned. */ eb = __alloc_dummy_extent_buffer(fs_info, nodesize / 2, len); Sector alignment is a hard requirement for any sector size. The only exception is superblock. But anything else should follow sector size alignment. This is definitely an invalid test case. This patch will fix both problems by: - Honor the sectorsize/nodesize combination Now we won't bother to hand-craft the length and use it as nodesize. - Use sectorsize as the 2nd run extent buffer start This would test the case where extent buffer is aligned to sectorsize but not always aligned to nodesize. Please note that, later subpage related cleanup will reduce extent_buffer::pages[] to exactly what we need, making the sector unaligned extent buffer operations cause problems. Since only extent_io self tests utilize this, this patch is required for all later cleanup/refactoring. Reviewed-by:
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Tom Rix authored
A semicolon is not needed after a switch statement. Signed-off-by:
Tom Rix <trix@redhat.com> Reviewed-by:
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Nikolay Borisov authored
The function is needlessly convoluted. Fix that by: * removing redundant sret variable definition in both if arms * replace the again/done labels with direct return statements, the function is short enough and doesn't do anything special upon exit * remove BUG_ON on split_node returning a positive number - it can't happen as split_node returns either 0 or a negative error code. Reviewed-by:
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Nikolay Borisov authored
At the point when we set 'ret = 0' it's guaranteed that the function is going to return 0 so directly return 0. No functional changes. Reviewed-by:
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Filipe Manana authored
At inode.c:cow_file_range_inline(), after we insert the inline extent in the fs/subvolume btree, we call btrfs_drop_extent_cache() to drop all extent maps in the file range, however that is not necessary because we have already done it in the call to btrfs_drop_extents(), which calls btrfs_drop_extent_cache() for us, and since at this point we have the file range locked in the inode's iotree (we are in the writeback path), we know no other task can come in and read stale file extent items or find none and therefore create either stale extent maps or an extent map that represents a hole. So just remove that unnecessary call to btrfs_drop_extent_cache(), as it's doing nothing and only wasting time. This call has been around since 2008, introduced in commit c8b97818 ("Btrfs: Add zlib compression support"), but even back then it seems it was not necessary, since we had the range locked in the inode's iotree and the call to btrfs_drop_extents() already used to always call btrfs_drop_extent_cache(). Reviewed-by:
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Filipe Manana authored
When joining a log transaction we acquire the root's log mutex, then increment the root's log batch and log writers counters while holding the mutex. However we don't need to increment the log batch there, because we are holding the mutex and incremented the log writers counter as well, so any other task trying to sync log will wait for the current task to finish its logging and still achieve the desired log batching. Since the log batch counter is an atomic counter and is incremented twice at the very beginning of the fsync callback (btrfs_sync_file()), once before flushing delalloc and once again after waiting for writeback to complete, eliminating its increment when joining the log transaction may provide some performance gains in case we have multiple concurrent tasks doing fsyncs against different files in the same subvolume, as it reduces contention on the atomic (locking the cacheline and bouncing it). When testing fio with 32 jobs, on a 8 cores VM, doing fsyncs against different files of the same subvolume, on top of a zram device, I could consistently see gains (higher throughput) between 1% to 2%, which is a very low value and possibly hard to be observed with a real device (I couldn't observe consistent gains with my low/mid end NVMe device). So this change is mostly motivated to just simplify the logic, as updating the log batch counter is only relevant when an fsync starts and while not holding the root's log mutex. Reviewed-by:
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Filipe Manana authored
Every time we log an inode we lookup in the fs/subvol tree for xattrs and if we have any, log them into the log tree. However it is very common to have inodes without any xattrs, so doing the search wastes times, but more importantly it adds contention on the fs/subvol tree locks, either making the logging code block and wait for tree locks or making the logging code making other concurrent operations block and wait. The most typical use cases where xattrs are used are when capabilities or ACLs are defined for an inode, or when SELinux is enabled. This change makes the logging code detect when an inode does not have xattrs and skip the xattrs search the next time the inode is logged, unless the inode is evicted and loaded again or a xattr is added to the inode. Therefore skipping the search for xattrs on inodes that don't ever have xattrs and are fsynced with some frequency. The following script that calls dbench was used to measure the impact of this change on a VM with 8 CPUs, 16Gb of ram, using a raw NVMe device directly (no intermediary filesystem on the host) and using a non-debug kernel (default configuration on Debian distributions): $ cat test.sh #!/bin/bash DEV=/dev/sdk MNT=/mnt/sdk MOUNT_OPTIONS="-o ssd" mkfs.btrfs -f -m single -d single $DEV mount $MOUNT_OPTIONS $DEV $MNT dbench -D $MNT -t 200 40 umount $MNT The results before this change: Operation Count AvgLat MaxLat ---------------------------------------- NTCreateX 5761605 0.172 312.057 Close 4232452 0.002 10.927 Rename 243937 1.406 277.344 Unlink 1163456 0.631 298.402 Deltree 160 11.581 221.107 Mkdir 80 0.003 0.005 Qpathinfo 5221410 0.065 122.309 Qfileinfo 915432 0.001 3.333 Qfsinfo 957555 0.003 3.992 Sfileinfo 469244 0.023 20.494 Find 2018865 0.448 123.659 WriteX 2874851 0.049 118.529 ReadX 9030579 0.004 21.654 LockX 18754 0.003 4.423 UnlockX 18754 0.002 0.331 Flush 403792 10.944 359.494 Throughput 908.444 MB/sec 40 clients 40 procs max_latency=359.500 ms The results after this change: Operation Count AvgLat MaxLat ---------------------------------------- NTCreateX 6442521 0.159 230.693 Close 4732357 0.002 10.972 Rename 272809 1.293 227.398 Unlink 1301059 0.563 218.500 Deltree 160 7.796 54.887 Mkdir 80 0.008 0.478 Qpathinfo 5839452 0.047 124.330 Qfileinfo 1023199 0.001 4.996 Qfsinfo 1070760 0.003 5.709 Sfileinfo 524790 0.033 21.765 Find 2257658 0.314 125.611 WriteX 3211520 0.040 232.135 ReadX 10098969 0.004 25.340 LockX 20974 0.003 1.569 UnlockX 20974 0.002 3.475 Flush 451553 10.287 331.037 Throughput 1011.77 MB/sec 40 clients 40 procs max_latency=331.045 ms +10.8% throughput, -8.2% max latency Reviewed-by:
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Nikolay Borisov authored
There are only 2 direct calls to set_extent_bit outside of extent-io - in btrfs_find_new_delalloc_bytes and btrfs_truncate_block, the rest are thin wrappers around __set_extent_bit. This adds unnecessary indirection and just makes it more annoying when looking at the various extent bit manipulation functions. This patch renames __set_extent_bit to set_extent_bit effectively removing a level of indirection. No functional changes. Signed-off-by:
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Nikolay Borisov authored
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Nikolay Borisov authored
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Nikolay Borisov authored
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Nikolay Borisov authored
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Nikolay Borisov authored
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Nikolay Borisov authored
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Nikolay Borisov authored
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Nikolay Borisov authored
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Nikolay Borisov authored
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Nikolay Borisov authored
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Nikolay Borisov authored
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Nikolay Borisov authored
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Nikolay Borisov authored
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Josef Bacik authored
It is unused everywhere now, it can be removed. Reviewed-by:
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Josef Bacik authored
It is completely unused now, remove it. Reviewed-by:
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Josef Bacik authored
We no longer use recursion, so __btrfs_tree_read_lock(BTRFS_NESTING_NORMAL) == btrfs_tree_read_lock. Replace this call with the simple helper. Reviewed-by:
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Josef Bacik authored
We no longer have recursive locking and there's no need for separate helpers that allowed the transition to rwsem with minimal code changes. Reviewed-by:
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Josef Bacik authored
Now that we're no longer using recursion, rip out all of the supporting code. Follow up patches will clean up the callers of these functions. The extent_buffer::lock_owner is still retained as it allows safety checks in btrfs_init_new_buffer for the case that the free space cache is corrupted and we try to allocate a block that we are currently using and have locked in the path. Reviewed-by:
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Josef Bacik authored
With my async free space cache loading patches ("btrfs: load free space cache asynchronously") we no longer have a user of path->recurse and can remove it. Reviewed-by: -
Josef Bacik authored
Filipe reported the following lockdep splat ====================================================== WARNING: possible circular locking dependency detected 5.10.0-rc2-btrfs-next-71 #1 Not tainted ------------------------------------------------------ find/324157 is trying to acquire lock: ffff8ebc48d293a0 (btrfs-tree-01#2/3){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] but task is already holding lock: ffff8eb9932c5088 (btrfs-tree-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (btrfs-tree-00){++++}-{3:3}: lock_acquire+0xd8/0x490 down_write_nested+0x44/0x120 __btrfs_tree_lock+0x27/0x120 [btrfs] btrfs_search_slot+0x2a3/0xc50 [btrfs] btrfs_insert_empty_items+0x58/0xa0 [btrfs] insert_with_overflow+0x44/0x110 [btrfs] btrfs_insert_xattr_item+0xb8/0x1d0 [btrfs] btrfs_setxattr+0xd6/0x4c0 [btrfs] btrfs_setxattr_trans+0x68/0x100 [btrfs] __vfs_setxattr+0x66/0x80 __vfs_setxattr_noperm+0x70/0x200 vfs_setxattr+0x6b/0x120 setxattr+0x125/0x240 path_setxattr+0xba/0xd0 __x64_sys_setxattr+0x27/0x30 do_syscall_64+0x33/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xa9 -> #0 (btrfs-tree-01#2/3){++++}-{3:3}: check_prev_add+0x91/0xc60 __lock_acquire+0x1689/0x3130 lock_acquire+0xd8/0x490 down_read_nested+0x45/0x220 __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] btrfs_next_old_leaf+0x27d/0x580 [btrfs] btrfs_real_readdir+0x1e3/0x4b0 [btrfs] iterate_dir+0x170/0x1c0 __x64_sys_getdents64+0x83/0x140 do_syscall_64+0x33/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xa9 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(btrfs-tree-00); lock(btrfs-tree-01#2/3); lock(btrfs-tree-00); lock(btrfs-tree-01#2/3); *** DEADLOCK *** 5 locks held by find/324157: #0: ffff8ebc502c6e00 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x4d/0x60 #1: ffff8eb97f689980 (&type->i_mutex_dir_key#10){++++}-{3:3}, at: iterate_dir+0x52/0x1c0 #2: ffff8ebaec00ca58 (btrfs-tree-02#2){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] #3: ffff8eb98f986f78 (btrfs-tree-01#2){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] #4: ffff8eb9932c5088 (btrfs-tree-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] stack backtrace: CPU: 2 PID: 324157 Comm: find Not tainted 5.10.0-rc2-btrfs-next-71 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 Call Trace: dump_stack+0x8d/0xb5 check_noncircular+0xff/0x110 ? mark_lock.part.0+0x468/0xe90 check_prev_add+0x91/0xc60 __lock_acquire+0x1689/0x3130 ? kvm_clock_read+0x14/0x30 ? kvm_sched_clock_read+0x5/0x10 lock_acquire+0xd8/0x490 ? __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] down_read_nested+0x45/0x220 ? __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] btrfs_next_old_leaf+0x27d/0x580 [btrfs] btrfs_real_readdir+0x1e3/0x4b0 [btrfs] iterate_dir+0x170/0x1c0 __x64_sys_getdents64+0x83/0x140 ? filldir+0x1d0/0x1d0 do_syscall_64+0x33/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xa9 This happens because btrfs_next_old_leaf searches down to our current key, and then walks up the path until we can move to the next slot, and then reads back down the path so we get the next leaf. However it doesn't unlock any lower levels until it replaces them with the new extent buffer. This is technically fine, but of course causes lockdep to complain, because we could be holding locks on lower levels while locking upper levels. Fix this by dropping all nodes below the level that we use as our new starting point before we start reading back down the path. This also allows us to drop the nested/recursive locking magic, because we're no longer locking two nodes at the same level anymore. Reported-by:
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