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2022-07-29NFSD: Optimize nfsd4_encode_operation()Chuck Lever
write_bytes_to_xdr_buf() is a generic way to place a variable-length data item in an already-reserved spot in the encoding buffer. However, it is costly, and here, it is unnecessary because the data item is fixed in size, the buffer destination address is always word-aligned, and the destination location is already in @p. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29nfsd: silence extraneous printk on nfsd.ko insertionJeff Layton
This printk pops every time nfsd.ko gets plugged in. Most kmods don't do that and this one is not very informative. Olaf's email address seems to be defunct at this point anyway. Just drop it. Cc: Olaf Kirch <okir@suse.com> Signed-off-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: limit the number of v4 clients to 1024 per 1GB of system memoryDai Ngo
Currently there is no limit on how many v4 clients are supported by the system. This can be a problem in systems with small memory configuration to function properly when a very large number of clients exist that creates memory shortage conditions. This patch enforces a limit of 1024 NFSv4 clients, including courtesy clients, per 1GB of system memory. When the number of the clients reaches the limit, requests that create new clients are returned with NFS4ERR_DELAY and the laundromat is kicked start to trim old clients. Due to the overhead of the upcall to remove the client record, the maximun number of clients the laundromat removes on each run is limited to 128. This is done to ensure the laundromat can still process the other tasks in a timely manner. Since there is now a limit of the number of clients, the 24-hr idle time limit of courtesy client is no longer needed and was removed. Signed-off-by: Dai Ngo <dai.ngo@oracle.com> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: keep track of the number of v4 clients in the systemDai Ngo
Add counter nfs4_client_count to keep track of the total number of v4 clients, including courtesy clients, in the system. Signed-off-by: Dai Ngo <dai.ngo@oracle.com> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: refactoring v4 specific code to a helper in nfs4state.cDai Ngo
This patch moves the v4 specific code from nfsd_init_net() to nfsd4_init_leases_net() helper in nfs4state.c Signed-off-by: Dai Ngo <dai.ngo@oracle.com> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Ensure nf_inode is never dereferencedChuck Lever
The documenting comment for struct nf_file states: /* * A representation of a file that has been opened by knfsd. These are hashed * in the hashtable by inode pointer value. Note that this object doesn't * hold a reference to the inode by itself, so the nf_inode pointer should * never be dereferenced, only used for comparison. */ Replace the two existing dereferences to make the comment always true. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: NFSv4 CLOSE should release an nfsd_file immediatelyChuck Lever
The last close of a file should enable other accessors to open and use that file immediately. Leaving the file open in the filecache prevents other users from accessing that file until the filecache garbage-collects the file -- sometimes that takes several seconds. Reported-by: Wang Yugui <wangyugui@e16-tech.com> Link: https://bugzilla.linux-nfs.org/show_bug.cgi?387 Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Move nfsd_file_trace_alloc() tracepointChuck Lever
Avoid recording the allocation of an nfsd_file item that is immediately released because a matching item was already inserted in the hash. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Separate tracepoints for acquire and createChuck Lever
These tracepoints collect different information: the create case does not open a file, so there's no nf_file available. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Clean up unused code after rhashtable conversionChuck Lever
Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Convert the filecache to use rhashtableChuck Lever
Enable the filecache hash table to start small, then grow with the workload. Smaller server deployments benefit because there should be lower memory utilization. Larger server deployments should see improved scaling with the number of open files. Suggested-by: Jeff Layton <jlayton@kernel.org> Suggested-by: Dave Chinner <david@fromorbit.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Set up an rhashtable for the filecacheChuck Lever
Add code to initialize and tear down an rhashtable. The rhashtable is not used yet. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Replace the "init once" mechanismChuck Lever
In a moment, the nfsd_file_hashtbl global will be replaced with an rhashtable. Replace the one or two spots that need to check if the hash table is available. We can easily reuse the SHUTDOWN flag for this purpose. Document that this mechanism relies on callers to hold the nfsd_mutex to prevent init, shutdown, and purging to run concurrently. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Remove nfsd_file::nf_hashvalChuck Lever
The value in this field can always be computed from nf_inode, thus it is no longer used. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: nfsd_file_hash_remove can compute hashvalChuck Lever
Remove an unnecessary use of nf_hashval. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Refactor __nfsd_file_close_inode()Chuck Lever
The code that computes the hashval is the same in both callers. To prevent them from going stale, reframe the documenting comments to remove descriptions of the underlying hash table structure, which is about to be replaced. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: nfsd_file_unhash can compute hashval from nf->nf_inodeChuck Lever
Remove an unnecessary usage of nf_hashval. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Remove lockdep assertion from unhash_and_release_locked()Chuck Lever
IIUC, holding the hash bucket lock is needed only in nfsd_file_unhash, and there is already a lockdep assertion there. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: No longer record nf_hashval in the trace logChuck Lever
I'm about to replace nfsd_file_hashtbl with an rhashtable. The individual hash values will no longer be visible or relevant, so remove them from the tracepoints. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Never call nfsd_file_gc() in foreground pathsChuck Lever
The checks in nfsd_file_acquire() and nfsd_file_put() that directly invoke filecache garbage collection are intended to keep cache occupancy between a low- and high-watermark. The reason to limit the capacity of the filecache is to keep filecache lookups reasonably fast. However, invoking garbage collection at those points has some undesirable negative impacts. Files that are held open by NFSv4 clients often push the occupancy of the filecache over these watermarks. At that point: - Every call to nfsd_file_acquire() and nfsd_file_put() results in an LRU walk. This has the same effect on lookup latency as long chains in the hash table. - Garbage collection will then run on every nfsd thread, causing a lot of unnecessary lock contention. - Limiting cache capacity pushes out files used only by NFSv3 clients, which are the type of files the filecache is supposed to help. To address those negative impacts, remove the direct calls to the garbage collector. Subsequent patches will address maintaining lookup efficiency as cache capacity increases. Suggested-by: Wang Yugui <wangyugui@e16-tech.com> Suggested-by: Dave Chinner <david@fromorbit.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Fix the filecache LRU shrinkerChuck Lever
Without LRU item rotation, the shrinker visits only a few items on the end of the LRU list, and those would always be long-term OPEN files for NFSv4 workloads. That makes the filecache shrinker completely ineffective. Adopt the same strategy as the inode LRU by using LRU_ROTATE. Suggested-by: Dave Chinner <david@fromorbit.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Leave open files out of the filecache LRUChuck Lever
There have been reports of problems when running fstests generic/531 against Linux NFS servers with NFSv4. The NFS server that hosts the test's SCRATCH_DEV suffers from CPU soft lock-ups during the test. Analysis shows that: fs/nfsd/filecache.c 482 ret = list_lru_walk(&nfsd_file_lru, 483 nfsd_file_lru_cb, 484 &head, LONG_MAX); causes nfsd_file_gc() to walk the entire length of the filecache LRU list every time it is called (which is quite frequently). The walk holds a spinlock the entire time that prevents other nfsd threads from accessing the filecache. What's more, for NFSv4 workloads, none of the items that are visited during this walk may be evicted, since they are all files that are held OPEN by NFS clients. Address this by ensuring that open files are not kept on the LRU list. Reported-by: Frank van der Linden <fllinden@amazon.com> Reported-by: Wang Yugui <wangyugui@e16-tech.com> Link: https://bugzilla.linux-nfs.org/show_bug.cgi?id=386 Suggested-by: Trond Myklebust <trond.myklebust@hammerspace.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Trace filecache LRU activityChuck Lever
Observe the operation of garbage collection and the lifetime of filecache items. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: WARN when freeing an item still linked via nf_lruChuck Lever
Add a guardrail to prevent freeing memory that is still on a list. This includes either a dispose list or the LRU list. This is the sign of a bug, but this class of bugs can be detected so that they don't endanger system stability, especially while debugging. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Hook up the filecache stat fileChuck Lever
There has always been the capability of exporting filecache metrics via /proc, but it was never hooked up. Let's surface these metrics to enable better observability of the filecache. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Zero counters when the filecache is re-initializedChuck Lever
If nfsd_file_cache_init() is called after a shutdown, be sure the stat counters are reset. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Record number of flush callsChuck Lever
Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Report the number of items evicted by the LRU walkChuck Lever
Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Refactor nfsd_file_lru_scan()Chuck Lever
Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Refactor nfsd_file_gc()Chuck Lever
Refactor nfsd_file_gc() to use the new list_lru helper. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Add nfsd_file_lru_dispose_list() helperChuck Lever
Refactor the invariant part of nfsd_file_lru_walk_list() into a separate helper function. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Report average age of filecache itemsChuck Lever
This is a measure of how long items stay in the filecache, to help assess how efficient the cache is. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Report count of freed filecache itemsChuck Lever
Surface the count of freed nfsd_file items. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Report count of calls to nfsd_file_acquire()Chuck Lever
Count the number of successful acquisitions that did not create a file (ie, acquisitions that do not result in a compulsory cache miss). This count can be compared directly with the reported hit count to compute a hit ratio. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Report filecache LRU sizeChuck Lever
Surface the NFSD filecache's LRU list length to help field troubleshooters monitor filecache issues. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Demote a WARN to a pr_warn()Chuck Lever
The call trace doesn't add much value, but it sure is noisy. Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29nfsd: remove redundant assignment to variable lenColin Ian King
Variable len is being assigned a value zero and this is never read, it is being re-assigned later. The assignment is redundant and can be removed. Cleans up clang scan-build warning: fs/nfsd/nfsctl.c:636:2: warning: Value stored to 'len' is never read Signed-off-by: Colin Ian King <colin.i.king@gmail.com> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Fix space and spelling mistakeZhang Jiaming
Add a blank space after ','. Change 'succesful' to 'successful'. Signed-off-by: Zhang Jiaming <jiaming@nfschina.com> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NFSD: Instrument fh_verify()Chuck Lever
Capture file handles and how they map to local inodes. In particular, NFSv4 PUTFH uses fh_verify() so we can now observe which file handles are the target of OPEN, LOOKUP, RENAME, and so on. Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29NLM: Defend against file_lock changes after vfs_test_lock()Benjamin Coddington
Instead of trusting that struct file_lock returns completely unchanged after vfs_test_lock() when there's no conflicting lock, stash away our nlm_lockowner reference so we can properly release it for all cases. This defends against another file_lock implementation overwriting fl_owner when the return type is F_UNLCK. Reported-by: Roberto Bergantinos Corpas <rbergant@redhat.com> Tested-by: Roberto Bergantinos Corpas <rbergant@redhat.com> Signed-off-by: Benjamin Coddington <bcodding@redhat.com> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-29nfsd: eliminate the NFSD_FILE_BREAK_* flagsJeff Layton
We had a report from the spring Bake-a-thon of data corruption in some nfstest_interop tests. Looking at the traces showed the NFS server allowing a v3 WRITE to proceed while a read delegation was still outstanding. Currently, we only set NFSD_FILE_BREAK_* flags if NFSD_MAY_NOT_BREAK_LEASE was set when we call nfsd_file_alloc. NFSD_MAY_NOT_BREAK_LEASE was intended to be set when finding files for COMMIT ops, where we need a writeable filehandle but don't need to break read leases. It doesn't make any sense to consult that flag when allocating a file since the file may be used on subsequent calls where we do want to break the lease (and the usage of it here seems to be reverse from what it should be anyway). Also, after calling nfsd_open_break_lease, we don't want to clear the BREAK_* bits. A lease could end up being set on it later (more than once) and we need to be able to break those leases as well. This means that the NFSD_FILE_BREAK_* flags now just mirror NFSD_MAY_{READ,WRITE} flags, so there's no need for them at all. Just drop those flags and unconditionally call nfsd_open_break_lease every time. Reported-by: Olga Kornieskaia <kolga@netapp.com> Link: https://bugzilla.redhat.com/show_bug.cgi?id=2107360 Fixes: 65294c1f2c5e (nfsd: add a new struct file caching facility to nfsd) Cc: <stable@vger.kernel.org> # 5.4.x : bb283ca18d1e NFSD: Clean up the show_nf_flags() macro Cc: <stable@vger.kernel.org> # 5.4.x Signed-off-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2022-07-28ovl: drop WARN_ON() dentry is NULL in ovl_encode_fh()Jiachen Zhang
Some code paths cannot guarantee the inode have any dentry alias. So WARN_ON() all !dentry may flood the kernel logs. For example, when an overlayfs inode is watched by inotifywait (1), and someone is trying to read the /proc/$(pidof inotifywait)/fdinfo/INOTIFY_FD, at that time if the dentry has been reclaimed by kernel (such as echo 2 > /proc/sys/vm/drop_caches), there will be a WARN_ON(). The printed call stack would be like: ? show_mark_fhandle+0xf0/0xf0 show_mark_fhandle+0x4a/0xf0 ? show_mark_fhandle+0xf0/0xf0 ? seq_vprintf+0x30/0x50 ? seq_printf+0x53/0x70 ? show_mark_fhandle+0xf0/0xf0 inotify_fdinfo+0x70/0x90 show_fdinfo.isra.4+0x53/0x70 seq_show+0x130/0x170 seq_read+0x153/0x440 vfs_read+0x94/0x150 ksys_read+0x5f/0xe0 do_syscall_64+0x59/0x1e0 entry_SYSCALL_64_after_hwframe+0x44/0xa9 So let's drop WARN_ON() to avoid kernel log flooding. Reported-by: Hongbo Yin <yinhongbo@bytedance.com> Signed-off-by: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com> Signed-off-by: Tianci Zhang <zhangtianci.1997@bytedance.com> Fixes: 8ed5eec9d6c4 ("ovl: encode pure upper file handles") Cc: <stable@vger.kernel.org> # v4.16 Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2022-07-28ovl: improve ovl_get_acl() if POSIX ACL support is offYang Xu
Provide a proper stub for the !CONFIG_FS_POSIX_ACL case. Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2022-07-28kernfs: Fix typo 'the the' in commentSlark Xiao
Replace 'the the' with 'the' in the comment. Signed-off-by: Slark Xiao <slark_xiao@163.com> Link: https://lore.kernel.org/r/20220722100518.79741-1-slark_xiao@163.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2022-07-27exec: Call kmap_local_page() in copy_string_kernel()Fabio M. De Francesco
The use of kmap_atomic() is being deprecated in favor of kmap_local_page(). With kmap_local_page(), the mappings are per thread, CPU local and not globally visible. Furthermore, the mappings can be acquired from any context (including interrupts). Therefore, replace kmap_atomic() with kmap_local_page() in copy_string_kernel(). Instead of open-coding local mapping + memcpy(), use memcpy_to_page(). Delete a redundant call to flush_dcache_page(). Tested with xfstests on a QEMU/ KVM x86_32 VM, 6GB RAM, booting a kernel with HIGHMEM64GB enabled. Suggested-by: Ira Weiny <ira.weiny@intel.com> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20220724212523.13317-1-fmdefrancesco@gmail.com
2022-07-27btrfs: reset RO counter on block group if we fail to relocateJosef Bacik
With the automatic block group reclaim code we will preemptively try to mark the block group RO before we start the relocation. We do this to make sure we should actually try to relocate the block group. However if we hit an error during the actual relocation we won't clean up our RO counter and the block group will remain RO. This was observed internally with file systems reporting less space available from df when we had failed background relocations. Fix this by doing the dec_ro in the error case. Fixes: 18bb8bbf13c1 ("btrfs: zoned: automatically reclaim zones") CC: stable@vger.kernel.org # 5.15+ Reviewed-by: Boris Burkov <boris@bur.io> Signed-off-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: David Sterba <dsterba@suse.com>
2022-07-27ovl: fix some kernel-doc commentsYang Li
Remove warnings found by running scripts/kernel-doc, which is caused by using 'make W=1'. fs/overlayfs/super.c:311: warning: Function parameter or member 'dentry' not described in 'ovl_statfs' fs/overlayfs/super.c:311: warning: Excess function parameter 'sb' description in 'ovl_statfs' fs/overlayfs/super.c:357: warning: Function parameter or member 'm' not described in 'ovl_show_options' fs/overlayfs/super.c:357: warning: Function parameter or member 'dentry' not described in 'ovl_show_options' Reported-by: Abaci Robot <abaci@linux.alibaba.com> Signed-off-by: Yang Li <yang.lee@linux.alibaba.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2022-07-27ovl: warn if trusted xattr creation failsMiklos Szeredi
When mounting overlayfs in an unprivileged user namespace, trusted xattr creation will fail. This will lead to failures in some file operations, e.g. in the following situation: mkdir lower upper work merged mkdir lower/directory mount -toverlay -olowerdir=lower,upperdir=upper,workdir=work none merged rmdir merged/directory mkdir merged/directory The last mkdir will fail: mkdir: cannot create directory 'merged/directory': Input/output error The cause for these failures is currently extremely non-obvious and hard to debug. Hence, warn the user and suggest using the userxattr mount option, if it is not already supplied and xattr creation fails during the self-check. Reported-by: Alois Wohlschlager <alois1@gmx-topmail.de> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2022-07-27NFSv4.1: RECLAIM_COMPLETE must handle EACCESZhang Xianwei
A client should be able to handle getting an EACCES error while doing a mount operation to reclaim state due to NFS4CLNT_RECLAIM_REBOOT being set. If the server returns RPC_AUTH_BADCRED because authentication failed when we execute "exportfs -au", then RECLAIM_COMPLETE will go a wrong way. After mount succeeds, all OPEN call will fail due to an NFS4ERR_GRACE error being returned. This patch is to fix it by resending a RPC request. Signed-off-by: Zhang Xianwei <zhang.xianwei8@zte.com.cn> Signed-off-by: Yi Wang <wang.yi59@zte.com.cn> Fixes: aa5190d0ed7d ("NFSv4: Kill nfs4_async_handle_error() abuses by NFSv4.1") Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2022-07-27fuse: retire block-device-based superblock on force unmountDaniil Lunev
Force unmount of FUSE severes the connection with the user space, even if there are still open files. Subsequent remount tries to re-use the superblock held by the open files, which is meaningless in the FUSE case after disconnect - reused super block doesn't have userspace counterpart attached to it and is incapable of doing any IO. This patch adds the functionality only for the block-device-based supers, since the primary use case of the feature is to gracefully handle force unmount of external devices, mounted with FUSE. This can be further extended to cover all superblocks, if the need arises. Signed-off-by: Daniil Lunev <dlunev@chromium.org> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>