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authorJeff Layton <jeff.layton@primarydata.com>2020-12-01 01:03:16 +0300
committerChuck Lever <chuck.lever@oracle.com>2020-12-09 17:39:38 +0300
commit7f84b488f9add1d5cca3e6197c95914c7bd3c1cf (patch)
treefe4616aeb70a824182f6fecd22a8ef6c38786ad7 /Documentation/filesystems
parentba5e8187c55555519ae0b63c0fb681391bc42af9 (diff)
downloadlinux-7f84b488f9add1d5cca3e6197c95914c7bd3c1cf.tar.xz
nfsd: close cached files prior to a REMOVE or RENAME that would replace target
It's not uncommon for some workloads to do a bunch of I/O to a file and delete it just afterward. If knfsd has a cached open file however, then the file may still be open when the dentry is unlinked. If the underlying filesystem is nfs, then that could trigger it to do a sillyrename. On a REMOVE or RENAME scan the nfsd_file cache for open files that correspond to the inode, and proactively unhash and put their references. This should prevent any delete-on-last-close activity from occurring, solely due to knfsd's open file cache. This must be done synchronously though so we use the variants that call flush_delayed_fput. There are deadlock possibilities if you call flush_delayed_fput while holding locks, however. In the case of nfsd_rename, we don't even do the lookups of the dentries to be renamed until we've locked for rename. Once we've figured out what the target dentry is for a rename, check to see whether there are cached open files associated with it. If there are, then unwind all of the locking, close them all, and then reattempt the rename. None of this is really necessary for "typical" filesystems though. It's mostly of use for NFS, so declare a new export op flag and use that to determine whether to close the files beforehand. Signed-off-by: Jeff Layton <jeff.layton@primarydata.com> Signed-off-by: Lance Shelton <lance.shelton@hammerspace.com> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Diffstat (limited to 'Documentation/filesystems')
-rw-r--r--Documentation/filesystems/nfs/exporting.rst13
1 files changed, 13 insertions, 0 deletions
diff --git a/Documentation/filesystems/nfs/exporting.rst b/Documentation/filesystems/nfs/exporting.rst
index 960be64446cb..0e98edd353b5 100644
--- a/Documentation/filesystems/nfs/exporting.rst
+++ b/Documentation/filesystems/nfs/exporting.rst
@@ -202,3 +202,16 @@ following flags are defined:
This flag exempts the filesystem from subtree checking and causes
exportfs to get back an error if it tries to enable subtree checking
on it.
+
+ EXPORT_OP_CLOSE_BEFORE_UNLINK - always close cached files before unlinking
+ On some exportable filesystems (such as NFS) unlinking a file that
+ is still open can cause a fair bit of extra work. For instance,
+ the NFS client will do a "sillyrename" to ensure that the file
+ sticks around while it's still open. When reexporting, that open
+ file is held by nfsd so we usually end up doing a sillyrename, and
+ then immediately deleting the sillyrenamed file just afterward when
+ the link count actually goes to zero. Sometimes this delete can race
+ with other operations (for instance an rmdir of the parent directory).
+ This flag causes nfsd to close any open files for this inode _before_
+ calling into the vfs to do an unlink or a rename that would replace
+ an existing file.