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During an incremental send, when an inode has multiple new references we might end up emitting rename operations for orphanizations that have a source path that is no longer valid due to a previous orphanization of some directory inode. This causes the receiver to fail since it tries to rename a path that does not exists. Example reproducer: $ cat reproducer.sh #!/bin/bash mkfs.btrfs -f /dev/sdi >/dev/null mount /dev/sdi /mnt/sdi touch /mnt/sdi/f1 touch /mnt/sdi/f2 mkdir /mnt/sdi/d1 mkdir /mnt/sdi/d1/d2 # Filesystem looks like: # # . (ino 256) # |----- f1 (ino 257) # |----- f2 (ino 258) # |----- d1/ (ino 259) # |----- d2/ (ino 260) btrfs subvolume snapshot -r /mnt/sdi /mnt/sdi/snap1 btrfs send -f /tmp/snap1.send /mnt/sdi/snap1 # Now do a series of changes such that: # # *) inode 258 has one new hardlink and the previous name changed # # *) both names conflict with the old names of two other inodes: # # 1) the new name "d1" conflicts with the old name of inode 259, # under directory inode 256 (root) # # 2) the new name "d2" conflicts with the old name of inode 260 # under directory inode 259 # # *) inodes 259 and 260 now have the old names of inode 258 # # *) inode 257 is now located under inode 260 - an inode with a number # smaller than the inode (258) for which we created a second hard # link and swapped its names with inodes 259 and 260 # ln /mnt/sdi/f2 /mnt/sdi/d1/f2_link mv /mnt/sdi/f1 /mnt/sdi/d1/d2/f1 # Swap d1 and f2. mv /mnt/sdi/d1 /mnt/sdi/tmp mv /mnt/sdi/f2 /mnt/sdi/d1 mv /mnt/sdi/tmp /mnt/sdi/f2 # Swap d2 and f2_link mv /mnt/sdi/f2/d2 /mnt/sdi/tmp mv /mnt/sdi/f2/f2_link /mnt/sdi/f2/d2 mv /mnt/sdi/tmp /mnt/sdi/f2/f2_link # Filesystem now looks like: # # . (ino 256) # |----- d1 (ino 258) # |----- f2/ (ino 259) # |----- f2_link/ (ino 260) # | |----- f1 (ino 257) # | # |----- d2 (ino 258) btrfs subvolume snapshot -r /mnt/sdi /mnt/sdi/snap2 btrfs send -f /tmp/snap2.send -p /mnt/sdi/snap1 /mnt/sdi/snap2 mkfs.btrfs -f /dev/sdj >/dev/null mount /dev/sdj /mnt/sdj btrfs receive -f /tmp/snap1.send /mnt/sdj btrfs receive -f /tmp/snap2.send /mnt/sdj umount /mnt/sdi umount /mnt/sdj When executed the receive of the incremental stream fails: $ ./reproducer.sh Create a readonly snapshot of '/mnt/sdi' in '/mnt/sdi/snap1' At subvol /mnt/sdi/snap1 Create a readonly snapshot of '/mnt/sdi' in '/mnt/sdi/snap2' At subvol /mnt/sdi/snap2 At subvol snap1 At snapshot snap2 ERROR: rename d1/d2 -> o260-6-0 failed: No such file or directory This happens because: 1) When processing inode 257 we end up computing the name for inode 259 because it is an ancestor in the send snapshot, and at that point it still has its old name, "d1", from the parent snapshot because inode 259 was not yet processed. We then cache that name, which is valid until we start processing inode 259 (or set the progress to 260 after processing its references); 2) Later we start processing inode 258 and collecting all its new references into the list sctx->new_refs. The first reference in the list happens to be the reference for name "d1" while the reference for name "d2" is next (the last element of the list). We compute the full path "d1/d2" for this second reference and store it in the reference (its ->full_path member). The path used for the new parent directory was "d1" and not "f2" because inode 259, the new parent, was not yet processed; 3) When we start processing the new references at process_recorded_refs() we start with the first reference in the list, for the new name "d1". Because there is a conflicting inode that was not yet processed, which is directory inode 259, we orphanize it, renaming it from "d1" to "o259-6-0"; 4) Then we start processing the new reference for name "d2", and we realize it conflicts with the reference of inode 260 in the parent snapshot. So we issue an orphanization operation for inode 260 by emitting a rename operation with a destination path of "o260-6-0" and a source path of "d1/d2" - this source path is the value we stored in the reference earlier at step 2), corresponding to the ->full_path member of the reference, however that path is no longer valid due to the orphanization of the directory inode 259 in step 3). This makes the receiver fail since the path does not exists, it should have been "o259-6-0/d2". Fix this by recomputing the full path of a reference before emitting an orphanization if we previously orphanized any directory, since that directory could be a parent in the new path. This is a rare scenario so keeping it simple and not checking if that previously orphanized directory is in fact an ancestor of the inode we are trying to orphanize. A test case for fstests follows soon. CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.