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Dominique Martinet
be2ca38253
This reverts commit724a08450f. This code simplification introduced significant regressions on servers that do not remap inode numbers when exporting multiple underlying filesystems with colliding inodes, as can be illustrated with simple tmpfs exports in qemu with remapping disabled: ``` # host side cd /tmp/linux-test mkdir m1 m2 mount -t tmpfs tmpfs m1 mount -t tmpfs tmpfs m2 mkdir m1/dir m2/dir echo foo > m1/dir/foo echo bar > m2/dir/bar # guest side # started with -virtfs local,path=/tmp/linux-test,mount_tag=tmp,security_model=mapped-file mount -t 9p -o trans=virtio,debug=1 tmp /mnt/t ls /mnt/t/m1/dir # foo ls /mnt/t/m2/dir # bar (works ok if directry isn't open) # cd to keep first dir's inode alive cd /mnt/t/m1/dir ls /mnt/t/m2/dir # foo (should be bar) ``` Other examples can be crafted with regular files with fscache enabled, in which case I/Os just happen to the wrong file leading to corruptions, or guest failing to boot with: | VFS: Lookup of 'com.android.runtime' in 9p 9p would have caused loop In theory, we'd want the servers to be smart enough and ensure they never send us two different files with the same 'qid.path', but while qemu has an option to remap that is recommended (and qemu prints a warning if this case happens), there are many other servers which do not (kvmtool, nfs-ganesha, probably diod...), we should at least ensure we don't cause regressions on this: - assume servers can't be trusted and operations that should get a 'new' inode properly do so. commitd05dcfdf5e(" fs/9p: mitigate inode collisions") attempted to do this, but v9fs_fid_iget_dotl() was not called so some higher level of caching got in the way; this needs to be fixed properly before we can re-apply the patches. - if we ever want to really simplify this code, we will need to add some negotiation with the server at mount time where the server could claim they handle this properly, at which point we could optimize this out. (but that might not be needed at all if we properly handle the 'new' check?) Fixes:724a08450f("fs/9p: simplify iget to remove unnecessary paths") Reported-by: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/all/20240408141436.GA17022@redhat.com/ Link: https://lkml.kernel.org/r/20240923100508.GA32066@willie-the-truck Cc: stable@vger.kernel.org # v6.9+ Message-ID: <20241024-revert_iget-v1-4-4cac63d25f72@codewreck.org> Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
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 reStructuredText 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.