In cases where we have transient errors, such as ENOSPC, it is important to ensure that errors are reported on all writes that may be affected. The problem we have is that not all errors are guaranteed to be reported at write time. Some are reported only when we call fsync(). In particular, this can be a problem for stable NFS writes. Since most filesystems protect the write to the page cache with the inode lock, but do not protect the subsequent call to generic_write_sync(), this means that if we have parallel writes to the same file, we can end up assigning the error to the wrong stable write call. If the application expects to be able to fix the transient errors, it may end up replaying the wrong write. One area where we have seen this happen is in flexfiles writes, where the server is capable of freeing up space on the DS in case of ENOSPC. The other area where we have seen a similar problem is when we have unstable writes, and the client sends a backgrounded commit in order to free up memory. If there are outstanding writes while the commit gets a transient error and bumps the write verifier, then we want to ensure that those writes get the approprite write verifier depending on whether they were affected by the fsync() or not. Right now, because the NFSv3 verifier is set in the XDR encoder well after the write is done, there is fairly large window for a race with a background commit. This patch series deals with both issues by adding per-file-descriptor locking that ensures that writes, fsync error handling, and write verifier updates are appropriately serialised. Trond Myklebust (9): nfsd: Allow nfsd_vfs_write() to take the nfsd_file as an argument nfsd: Fix stable writes nfsd: Update the boot verifier on stable writes too. nfsd: Pass the nfsd_file as arguments to nfsd4_clone_file_range() nfsd: Ensure exclusion between CLONE and WRITE errors sunrpc: Fix potential leaks in sunrpc_cache_unhash() sunrpc: clean up cache entry add/remove from hashtable nfsd: Ensure sampling of the commit verifier is atomic with the commit nfsd: Ensure sampling of the write verifier is atomic with the write fs/nfsd/filecache.c | 1 + fs/nfsd/filecache.h | 1 + fs/nfsd/nfs3proc.c | 5 +-- fs/nfsd/nfs3xdr.c | 16 +++------ fs/nfsd/nfs4proc.c | 14 ++++---- fs/nfsd/nfsproc.c | 2 +- fs/nfsd/vfs.c | 79 ++++++++++++++++++++++++++++++++++----------- fs/nfsd/vfs.h | 16 +++++---- fs/nfsd/xdr3.h | 2 ++ net/sunrpc/cache.c | 48 ++++++++++++++------------- 10 files changed, 115 insertions(+), 69 deletions(-) -- 2.24.1
