kernel/git/stable/linux.git/fs/btrfs/send.c, branch linux-5.3.y

Btrfs: send, skip backreference walking for extents with many references

2019-12-17T19:07:34+00:00

commit fd0ddbe2509568b00df364156f47561e9f469f15 upstream. Backreference walking, which is used by send to figure if it can issue clone operations instead of write operations, can be very slow and use too much memory when extents have many references. This change simply skips backreference walking when an extent has more than 64 references, in which case we fallback to a write operation instead of a clone operation. This limit is conservative and in practice I observed no signicant slowdown with up to 100 references and still low memory usage up to that limit. This is a temporary workaround until there are speedups in the backref walking code, and as such it does not attempt to add extra interfaces or knobs to tweak the threshold. Reported-by: Atemu Link: https://lore.kernel.org/linux-btrfs/CAE4GHgkvqVADtS4AzcQJxo0Q1jKQgKaW3JGp3SGdoinVo=C9eQ@mail.gmail.com/T/#me55dc0987f9cc2acaa54372ce0492c65782be3fa CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Qu Wenruo Signed-off-by: Filipe Manana Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman

btrfs: silence maybe-uninitialized warning in clone_range

2019-11-06T12:08:29+00:00

[ Upstream commit 431d39887d6273d6d84edf3c2eab09f4200e788a ] GCC throws warning message as below: ‘clone_src_i_size’ may be used uninitialized in this function [-Wmaybe-uninitialized] #define IS_ALIGNED(x, a) (((x) & ((typeof(x))(a) - 1)) == 0) ^ fs/btrfs/send.c:5088:6: note: ‘clone_src_i_size’ was declared here u64 clone_src_i_size; ^ The clone_src_i_size is only used as call-by-reference in a call to get_inode_info(). Silence the warning by initializing clone_src_i_size to 0. Note that the warning is a false positive and reported by older versions of GCC (eg. 7.x) but not eg 9.x. As there have been numerous people, the patch is applied. Setting clone_src_i_size to 0 does not otherwise make sense and would not do any action in case the code changes in the future. Signed-off-by: Austin Kim Reviewed-by: David Sterba [ add note ] Signed-off-by: David Sterba Signed-off-by: Sasha Levin

Btrfs: fix incremental send failure after deduplication

2019-07-30T16:25:11+00:00

When doing an incremental send operation we can fail if we previously did deduplication operations against a file that exists in both snapshots. In that case we will fail the send operation with -EIO and print a message to dmesg/syslog like the following: BTRFS error (device sdc): Send: inconsistent snapshot, found updated \ extent for inode 257 without updated inode item, send root is 258, \ parent root is 257 This requires that we deduplicate to the same file in both snapshots for the same amount of times on each snapshot. The issue happens because a deduplication only updates the iversion of an inode and does not update any other field of the inode, therefore if we deduplicate the file on each snapshot for the same amount of time, the inode will have the same iversion value (stored as the "sequence" field on the inode item) on both snapshots, therefore it will be seen as unchanged between in the send snapshot while there are new/updated/deleted extent items when comparing to the parent snapshot. This makes the send operation return -EIO and print an error message. Example reproducer: $ mkfs.btrfs -f /dev/sdb $ mount /dev/sdb /mnt # Create our first file. The first half of the file has several 64Kb # extents while the second half as a single 512Kb extent. $ xfs_io -f -s -c "pwrite -S 0xb8 -b 64K 0 512K" /mnt/foo $ xfs_io -c "pwrite -S 0xb8 512K 512K" /mnt/foo # Create the base snapshot and the parent send stream from it. $ btrfs subvolume snapshot -r /mnt /mnt/mysnap1 $ btrfs send -f /tmp/1.snap /mnt/mysnap1 # Create our second file, that has exactly the same data as the first # file. $ xfs_io -f -c "pwrite -S 0xb8 0 1M" /mnt/bar # Create the second snapshot, used for the incremental send, before # doing the file deduplication. $ btrfs subvolume snapshot -r /mnt /mnt/mysnap2 # Now before creating the incremental send stream: # # 1) Deduplicate into a subrange of file foo in snapshot mysnap1. This # will drop several extent items and add a new one, also updating # the inode's iversion (sequence field in inode item) by 1, but not # any other field of the inode; # # 2) Deduplicate into a different subrange of file foo in snapshot # mysnap2. This will replace an extent item with a new one, also # updating the inode's iversion by 1 but not any other field of the # inode. # # After these two deduplication operations, the inode items, for file # foo, are identical in both snapshots, but we have different extent # items for this inode in both snapshots. We want to check this doesn't # cause send to fail with an error or produce an incorrect stream. $ xfs_io -r -c "dedupe /mnt/bar 0 0 512K" /mnt/mysnap1/foo $ xfs_io -r -c "dedupe /mnt/bar 512K 512K 512K" /mnt/mysnap2/foo # Create the incremental send stream. $ btrfs send -p /mnt/mysnap1 -f /tmp/2.snap /mnt/mysnap2 ERROR: send ioctl failed with -5: Input/output error This issue started happening back in 2015 when deduplication was updated to not update the inode's ctime and mtime and update only the iversion. Back then we would hit a BUG_ON() in send, but later in 2016 send was updated to return -EIO and print the error message instead of doing the BUG_ON(). A test case for fstests follows soon. Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203933 Fixes: 1c919a5e13702c ("btrfs: don't update mtime/ctime on deduped inodes") CC: stable@vger.kernel.org # 4.4+ Signed-off-by: Filipe Manana Signed-off-by: David Sterba

Btrfs: prevent send failures and crashes due to concurrent relocation

2019-07-02T10:30:49+00:00

Send always operates on read-only trees and always expected that while it is in progress, nothing changes in those trees. Due to that expectation and the fact that send is a read-only operation, it operates on commit roots and does not hold transaction handles. However relocation can COW nodes and leafs from read-only trees, which can cause unexpected failures and crashes (hitting BUG_ONs). while send using a node/leaf, it gets COWed, the transaction used to COW it is committed, a new transaction starts, the extent previously used for that node/leaf gets allocated, possibly for another tree, and the respective extent buffer' content changes while send is still using it. When this happens send normally fails with EIO being returned to user space and messages like the following are found in dmesg/syslog: [ 3408.699121] BTRFS error (device sdc): parent transid verify failed on 58703872 wanted 250 found 253 [ 3441.523123] BTRFS error (device sdc): did not find backref in send_root. inode=63211, offset=0, disk_byte=5222825984 found extent=5222825984 Other times, less often, we hit a BUG_ON() because an extent buffer that send is using used to be a node, and while send is still using it, it got COWed and got reused as a leaf while send is still using, producing the following trace: [ 3478.466280] ------------[ cut here ]------------ [ 3478.466282] kernel BUG at fs/btrfs/ctree.c:1806! [ 3478.466965] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC PTI [ 3478.467635] CPU: 0 PID: 2165 Comm: btrfs Not tainted 5.0.0-btrfs-next-46 #1 [ 3478.468311] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.2-0-gf9626ccb91-prebuilt.qemu-project.org 04/01/2014 [ 3478.469681] RIP: 0010:read_node_slot+0x122/0x130 [btrfs] (...) [ 3478.471758] RSP: 0018:ffffa437826bfaa0 EFLAGS: 00010246 [ 3478.472457] RAX: ffff961416ed7000 RBX: 000000000000003d RCX: 0000000000000002 [ 3478.473151] RDX: 000000000000003d RSI: ffff96141e387408 RDI: ffff961599b30000 [ 3478.473837] RBP: ffffa437826bfb8e R08: 0000000000000001 R09: ffffa437826bfb8e [ 3478.474515] R10: ffffa437826bfa70 R11: 0000000000000000 R12: ffff9614385c8708 [ 3478.475186] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 [ 3478.475840] FS: 00007f8e0e9cc8c0(0000) GS:ffff9615b6a00000(0000) knlGS:0000000000000000 [ 3478.476489] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 3478.477127] CR2: 00007f98b67a056e CR3: 0000000005df6005 CR4: 00000000003606f0 [ 3478.477762] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 3478.478385] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 3478.479003] Call Trace: [ 3478.479600] ? do_raw_spin_unlock+0x49/0xc0 [ 3478.480202] tree_advance+0x173/0x1d0 [btrfs] [ 3478.480810] btrfs_compare_trees+0x30c/0x690 [btrfs] [ 3478.481388] ? process_extent+0x1280/0x1280 [btrfs] [ 3478.481954] btrfs_ioctl_send+0x1037/0x1270 [btrfs] [ 3478.482510] _btrfs_ioctl_send+0x80/0x110 [btrfs] [ 3478.483062] btrfs_ioctl+0x13fe/0x3120 [btrfs] [ 3478.483581] ? rq_clock_task+0x2e/0x60 [ 3478.484086] ? wake_up_new_task+0x1f3/0x370 [ 3478.484582] ? do_vfs_ioctl+0xa2/0x6f0 [ 3478.485075] ? btrfs_ioctl_get_supported_features+0x30/0x30 [btrfs] [ 3478.485552] do_vfs_ioctl+0xa2/0x6f0 [ 3478.486016] ? __fget+0x113/0x200 [ 3478.486467] ksys_ioctl+0x70/0x80 [ 3478.486911] __x64_sys_ioctl+0x16/0x20 [ 3478.487337] do_syscall_64+0x60/0x1b0 [ 3478.487751] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 3478.488159] RIP: 0033:0x7f8e0d7d4dd7 (...) [ 3478.489349] RSP: 002b:00007ffcf6fb4908 EFLAGS: 00000202 ORIG_RAX: 0000000000000010 [ 3478.489742] RAX: ffffffffffffffda RBX: 0000000000000105 RCX: 00007f8e0d7d4dd7 [ 3478.490142] RDX: 00007ffcf6fb4990 RSI: 0000000040489426 RDI: 0000000000000005 [ 3478.490548] RBP: 0000000000000005 R08: 00007f8e0d6f3700 R09: 00007f8e0d6f3700 [ 3478.490953] R10: 00007f8e0d6f39d0 R11: 0000000000000202 R12: 0000000000000005 [ 3478.491343] R13: 00005624e0780020 R14: 0000000000000000 R15: 0000000000000001 (...) [ 3478.493352] ---[ end trace d5f537302be4f8c8 ]--- Another possibility, much less likely to happen, is that send will not fail but the contents of the stream it produces may not be correct. To avoid this, do not allow send and relocation (balance) to run in parallel. In the long term the goal is to allow for both to be able to run concurrently without any problems, but that will take a significant effort in development and testing. Signed-off-by: Filipe Manana Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: resurrect btrfs_crc32c()

2019-07-01T11:35:00+00:00

Commit 9678c54388b6 ("btrfs: Remove custom crc32c init code") removed the btrfs_crc32c() function, because it was a duplicate of the crc32c() library function we already have in the kernel. Resurrect it as a shim wrapper over crc32c() to make following transformations of the checksumming code in btrfs easier. Also provide a btrfs_crc32_final() to ease following transformations. Reviewed-by: Nikolay Borisov Signed-off-by: Johannes Thumshirn Reviewed-by: David Sterba Signed-off-by: David Sterba

Btrfs: incremental send, fix emission of invalid clone operations

2019-05-28T16:54:10+00:00

When doing an incremental send we can now issue clone operations with a source range that ends at the source's file eof and with a destination range that ends at an offset smaller then the destination's file eof. If the eof of the source file is not aligned to the sector size of the filesystem, the receiver will get a -EINVAL error when trying to do the operation or, on older kernels, silently corrupt the destination file. The corruption happens on kernels without commit ac765f83f1397646 ("Btrfs: fix data corruption due to cloning of eof block"), while the failure to clone happens on kernels with that commit. Example reproducer: $ mkfs.btrfs -f /dev/sdb $ mount /dev/sdb /mnt/sdb $ xfs_io -f -c "pwrite -S 0xb1 0 2M" /mnt/sdb/foo $ xfs_io -f -c "pwrite -S 0xc7 0 2M" /mnt/sdb/bar $ xfs_io -f -c "pwrite -S 0x4d 0 2M" /mnt/sdb/baz $ xfs_io -f -c "pwrite -S 0xe2 0 2M" /mnt/sdb/zoo $ btrfs subvolume snapshot -r /mnt/sdb /mnt/sdb/base $ btrfs send -f /tmp/base.send /mnt/sdb/base $ xfs_io -c "reflink /mnt/sdb/bar 1560K 500K 100K" /mnt/sdb/bar $ xfs_io -c "reflink /mnt/sdb/bar 1560K 0 100K" /mnt/sdb/zoo $ xfs_io -c "truncate 550K" /mnt/sdb/bar $ btrfs subvolume snapshot -r /mnt/sdb /mnt/sdb/incr $ btrfs send -f /tmp/incr.send -p /mnt/sdb/base /mnt/sdb/incr $ mkfs.btrfs -f /dev/sdc $ mount /dev/sdc /mnt/sdc $ btrfs receive -f /tmp/base.send /mnt/sdc $ btrfs receive -vv -f /tmp/incr.send /mnt/sdc (...) truncate bar size=563200 utimes bar clone zoo - source=bar source offset=512000 offset=0 length=51200 ERROR: failed to clone extents to zoo Invalid argument The failure happens because the clone source range ends at the eof of file bar, 563200, which is not aligned to the filesystems sector size (4Kb in this case), and the destination range ends at offset 0 + 51200, which is less then the size of the file zoo (2Mb). So fix this by detecting such case and instead of issuing a clone operation for the whole range, do a clone operation for smaller range that is sector size aligned followed by a write operation for the block containing the eof. Here we will always be pessimistic and assume the destination filesystem of the send stream has the largest possible sector size (64Kb), since we have no way of determining it. This fixes a recent regression introduced in kernel 5.2-rc1. Fixes: 040ee6120cb6706 ("Btrfs: send, improve clone range") Signed-off-by: Filipe Manana Signed-off-by: David Sterba

Btrfs: incremental send, fix file corruption when no-holes feature is enabled

2019-05-28T16:54:10+00:00

When using the no-holes feature, if we have a file with prealloc extents with a start offset beyond the file's eof, doing an incremental send can cause corruption of the file due to incorrect hole detection. Such case requires that the prealloc extent(s) exist in both the parent and send snapshots, and that a hole is punched into the file that covers all its extents that do not cross the eof boundary. Example reproducer: $ mkfs.btrfs -f -O no-holes /dev/sdb $ mount /dev/sdb /mnt/sdb $ xfs_io -f -c "pwrite -S 0xab 0 500K" /mnt/sdb/foobar $ xfs_io -c "falloc -k 1200K 800K" /mnt/sdb/foobar $ btrfs subvolume snapshot -r /mnt/sdb /mnt/sdb/base $ btrfs send -f /tmp/base.snap /mnt/sdb/base $ xfs_io -c "fpunch 0 500K" /mnt/sdb/foobar $ btrfs subvolume snapshot -r /mnt/sdb /mnt/sdb/incr $ btrfs send -p /mnt/sdb/base -f /tmp/incr.snap /mnt/sdb/incr $ md5sum /mnt/sdb/incr/foobar 816df6f64deba63b029ca19d880ee10a /mnt/sdb/incr/foobar $ mkfs.btrfs -f /dev/sdc $ mount /dev/sdc /mnt/sdc $ btrfs receive -f /tmp/base.snap /mnt/sdc $ btrfs receive -f /tmp/incr.snap /mnt/sdc $ md5sum /mnt/sdc/incr/foobar cf2ef71f4a9e90c2f6013ba3b2257ed2 /mnt/sdc/incr/foobar --> Different checksum, because the prealloc extent beyond the file's eof confused the hole detection code and it assumed a hole starting at offset 0 and ending at the offset of the prealloc extent (1200Kb) instead of ending at the offset 500Kb (the file's size). Fix this by ensuring we never cross the file's size when issuing the write operations for a hole. Fixes: 16e7549f045d33 ("Btrfs: incompatible format change to remove hole extents") CC: stable@vger.kernel.org # 3.14+ Signed-off-by: Filipe Manana Signed-off-by: David Sterba

Btrfs: fix race between send and deduplication that lead to failures and crashes

2019-04-29T17:02:52+00:00

Send operates on read only trees and expects them to never change while it is using them. This is part of its initial design, and this expection is due to two different reasons: 1) When it was introduced, no operations were allowed to modifiy read-only subvolumes/snapshots (including defrag for example). 2) It keeps send from having an impact on other filesystem operations. Namely send does not need to keep locks on the trees nor needs to hold on to transaction handles and delay transaction commits. This ends up being a consequence of the former reason. However the deduplication feature was introduced later (on September 2013, while send was introduced in July 2012) and it allowed for deduplication with destination files that belong to read-only trees (subvolumes and snapshots). That means that having a send operation (either full or incremental) running in parallel with a deduplication that has the destination inode in one of the trees used by the send operation, can result in tree nodes and leaves getting freed and reused while send is using them. This problem is similar to the problem solved for the root nodes getting freed and reused when a snapshot is made against one tree that is currenly being used by a send operation, fixed in commits [1] and [2]. These commits explain in detail how the problem happens and the explanation is valid for any node or leaf that is not the root of a tree as well. This problem was also discussed and explained recently in a thread [3]. The problem is very easy to reproduce when using send with large trees (snapshots) and just a few concurrent deduplication operations that target files in the trees used by send. A stress test case is being sent for fstests that triggers the issue easily. The most common error to hit is the send ioctl return -EIO with the following messages in dmesg/syslog: [1631617.204075] BTRFS error (device sdc): did not find backref in send_root. inode=63292, offset=0, disk_byte=5228134400 found extent=5228134400 [1631633.251754] BTRFS error (device sdc): parent transid verify failed on 32243712 wanted 24 found 27 The first one is very easy to hit while the second one happens much less frequently, except for very large trees (in that test case, snapshots with 100000 files having large xattrs to get deep and wide trees). Less frequently, at least one BUG_ON can be hit: [1631742.130080] ------------[ cut here ]------------ [1631742.130625] kernel BUG at fs/btrfs/ctree.c:1806! [1631742.131188] invalid opcode: 0000 [#6] SMP DEBUG_PAGEALLOC PTI [1631742.131726] CPU: 1 PID: 13394 Comm: btrfs Tainted: G B D W 5.0.0-rc8-btrfs-next-45 #1 [1631742.132265] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.2-0-gf9626ccb91-prebuilt.qemu-project.org 04/01/2014 [1631742.133399] RIP: 0010:read_node_slot+0x122/0x130 [btrfs] (...) [1631742.135061] RSP: 0018:ffffb530021ebaa0 EFLAGS: 00010246 [1631742.135615] RAX: ffff93ac8912e000 RBX: 000000000000009d RCX: 0000000000000002 [1631742.136173] RDX: 000000000000009d RSI: ffff93ac564b0d08 RDI: ffff93ad5b48c000 [1631742.136759] RBP: ffffb530021ebb7d R08: 0000000000000001 R09: ffffb530021ebb7d [1631742.137324] R10: ffffb530021eba70 R11: 0000000000000000 R12: ffff93ac87d0a708 [1631742.137900] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000001 [1631742.138455] FS: 00007f4cdb1528c0(0000) GS:ffff93ad76a80000(0000) knlGS:0000000000000000 [1631742.139010] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [1631742.139568] CR2: 00007f5acb3d0420 CR3: 000000012be3e006 CR4: 00000000003606e0 [1631742.140131] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [1631742.140719] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [1631742.141272] Call Trace: [1631742.141826] ? do_raw_spin_unlock+0x49/0xc0 [1631742.142390] tree_advance+0x173/0x1d0 [btrfs] [1631742.142948] btrfs_compare_trees+0x268/0x690 [btrfs] [1631742.143533] ? process_extent+0x1070/0x1070 [btrfs] [1631742.144088] btrfs_ioctl_send+0x1037/0x1270 [btrfs] [1631742.144645] _btrfs_ioctl_send+0x80/0x110 [btrfs] [1631742.145161] ? trace_sched_stick_numa+0xe0/0xe0 [1631742.145685] btrfs_ioctl+0x13fe/0x3120 [btrfs] [1631742.146179] ? account_entity_enqueue+0xd3/0x100 [1631742.146662] ? reweight_entity+0x154/0x1a0 [1631742.147135] ? update_curr+0x20/0x2a0 [1631742.147593] ? check_preempt_wakeup+0x103/0x250 [1631742.148053] ? do_vfs_ioctl+0xa2/0x6f0 [1631742.148510] ? btrfs_ioctl_get_supported_features+0x30/0x30 [btrfs] [1631742.148942] do_vfs_ioctl+0xa2/0x6f0 [1631742.149361] ? __fget+0x113/0x200 [1631742.149767] ksys_ioctl+0x70/0x80 [1631742.150159] __x64_sys_ioctl+0x16/0x20 [1631742.150543] do_syscall_64+0x60/0x1b0 [1631742.150931] entry_SYSCALL_64_after_hwframe+0x49/0xbe [1631742.151326] RIP: 0033:0x7f4cd9f5add7 (...) [1631742.152509] RSP: 002b:00007ffe91017708 EFLAGS: 00000202 ORIG_RAX: 0000000000000010 [1631742.152892] RAX: ffffffffffffffda RBX: 0000000000000105 RCX: 00007f4cd9f5add7 [1631742.153268] RDX: 00007ffe91017790 RSI: 0000000040489426 RDI: 0000000000000007 [1631742.153633] RBP: 0000000000000007 R08: 00007f4cd9e79700 R09: 00007f4cd9e79700 [1631742.153999] R10: 00007f4cd9e799d0 R11: 0000000000000202 R12: 0000000000000003 [1631742.154365] R13: 0000555dfae53020 R14: 0000000000000000 R15: 0000000000000001 (...) [1631742.156696] ---[ end trace 5dac9f96dcc3fd6b ]--- That BUG_ON happens because while send is using a node, that node is COWed by a concurrent deduplication, gets freed and gets reused as a leaf (because a transaction commit happened in between), so when it attempts to read a slot from the extent buffer, at ctree.c:read_node_slot(), the extent buffer contents were wiped out and it now matches a leaf (which can even belong to some other tree now), hitting the BUG_ON(level == 0). Fix this concurrency issue by not allowing send and deduplication to run in parallel if both operate on the same readonly trees, returning EAGAIN to user space and logging an exlicit warning in dmesg/syslog. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=be6821f82c3cc36e026f5afd10249988852b35ea [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6f2f0b394b54e2b159ef969a0b5274e9bbf82ff2 [3] https://lore.kernel.org/linux-btrfs/CAL3q7H7iqSEEyFaEtpRZw3cp613y+4k2Q8b4W7mweR3tZA05bQ@mail.gmail.com/ CC: stable@vger.kernel.org # 4.4+ Signed-off-by: Filipe Manana Reviewed-by: David Sterba Signed-off-by: David Sterba

Btrfs: send, flush dellaloc in order to avoid data loss

2019-04-29T17:02:51+00:00

When we set a subvolume to read-only mode we do not flush dellaloc for any of its inodes (except if the filesystem is mounted with -o flushoncommit), since it does not affect correctness for any subsequent operations - except for a future send operation. The send operation will not be able to see the delalloc data since the respective file extent items, inode item updates, backreferences, etc, have not hit yet the subvolume and extent trees. Effectively this means data loss, since the send stream will not contain any data from existing delalloc. Another problem from this is that if the writeback starts and finishes while the send operation is in progress, we have the subvolume tree being being modified concurrently which can result in send failing unexpectedly with EIO or hitting runtime errors, assertion failures or hitting BUG_ONs, etc. Simple reproducer: $ mkfs.btrfs -f /dev/sdb $ mount /dev/sdb /mnt $ btrfs subvolume create /mnt/sv $ xfs_io -f -c "pwrite -S 0xea 0 108K" /mnt/sv/foo $ btrfs property set /mnt/sv ro true $ btrfs send -f /tmp/send.stream /mnt/sv $ od -t x1 -A d /mnt/sv/foo 0000000 ea ea ea ea ea ea ea ea ea ea ea ea ea ea ea ea * 0110592 $ umount /mnt $ mkfs.btrfs -f /dev/sdc $ mount /dev/sdc /mnt $ btrfs receive -f /tmp/send.stream /mnt $ echo $? 0 $ od -t x1 -A d /mnt/sv/foo 0000000 # ---> empty file Since this a problem that affects send only, fix it in send by flushing dellaloc for all the roots used by the send operation before send starts to process the commit roots. This is a problem that affects send since it was introduced (commit 31db9f7c23fbf7 ("Btrfs: introduce BTRFS_IOC_SEND for btrfs send/receive")) but backporting it to older kernels has some dependencies: - For kernels between 3.19 and 4.20, it depends on commit 3cd24c698004d2 ("btrfs: use tagged writepage to mitigate livelock of snapshot") because the function btrfs_start_delalloc_snapshot() does not exist before that commit. So one has to either pick that commit or replace the calls to btrfs_start_delalloc_snapshot() in this patch with calls to btrfs_start_delalloc_inodes(). - For kernels older than 3.19 it also requires commit e5fa8f865b3324 ("Btrfs: ensure send always works on roots without orphans") because it depends on the function ensure_commit_roots_uptodate() which that commits introduced. - No dependencies for 5.0+ kernels. A test case for fstests follows soon. CC: stable@vger.kernel.org # 3.19+ Signed-off-by: Filipe Manana Signed-off-by: David Sterba

Btrfs: send, improve clone range

2019-04-29T17:02:35+00:00

Improve clone_range in two scenarios. 1. Remove the limit of inode size when find clone inodes We can do partial clone, so there is no need to limit the size of the candidate inode. When clone a range, we clone the legal range only by bytenr, offset, len, inode size. 2. In the scenarios of rewrite or clone_range, data_offset rarely matches exactly, so the chance of a clone is missed. e.g. 1. Write a 1M file dd if=/dev/zero of=1M bs=1M count=1 2. Clone 1M file cp --reflink 1M clone 3. Rewrite 4k on the clone file dd if=/dev/zero of=clone bs=4k count=1 conv=notrunc The disk layout is as follows: item 16 key (257 EXTENT_DATA 0) itemoff 15353 itemsize 53 extent data disk byte 1103101952 nr 1048576 extent data offset 0 nr 1048576 ram 1048576 extent compression(none) ... item 22 key (258 EXTENT_DATA 0) itemoff 14959 itemsize 53 extent data disk byte 1104150528 nr 4096 extent data offset 0 nr 4096 ram 4096 extent compression(none) item 23 key (258 EXTENT_DATA 4096) itemoff 14906 itemsize 53 extent data disk byte 1103101952 nr 1048576 extent data offset 4096 nr 1044480 ram 1048576 extent compression(none) When send, inode 258 file offset 4096~1048576 (item 23) has a chance to clone_range, but because data_offset does not match inode 257 (item 16), it causes missed clone and can only transfer actual data. Improve the problem by judging whether the current data_offset has overlap with the file extent item, and if so, adjusting offset and extent_len so that we can clone correctly. Reviewed-by: Filipe Manana Signed-off-by: Robbie Ko Signed-off-by: David Sterba