Recently, a number of changes went into the kernel to try to ensure that I/O errors (specifically write errors) are reported to the application once and only once. The vehicle for ensuring the errors are reported is the struct file, which uses the 'f_wb_err' field to track which errors have been reported. The problem is that errors are mainly intended to be reported through fsync(). If the client is doing synchronous writes, then all is well, but if it is doing unstable writes, then the errors may not be reported until the client calls COMMIT. If the file cache has thrown out the struct file, due to memory pressure, or just because the client took a long while between the last WRITE and the COMMIT, then the error report may be lost, and the client may just think its data is safely stored. Note that the problem is compounded by the fact that NFSv3 is stateless, so the server never knows that the client may have rebooted, so there can be no guarantee that a COMMIT will ever be sent. The following patch set attempts to remedy the situation using 2 strategies: 1) If the inode is dirty, then avoid garbage collecting the file from the file cache. 2) If the file is closed, and we see that it would have reported an error to COMMIT, then we bump the boot verifier in order to ensure the client retransmits all its writes. Note that if multiple clients were writing to the same file, then we probably want to bump the boot verifier anyway, since only one COMMIT will see the error report (because the cached file is also shared). So in order to implement the above strategy, we first have to do the following: split up the file cache to act per net namespace, since the boot verifier is per net namespace. Then add a helper to update the boot verifier. Trond Myklebust (3): nfsd: nfsd_file cache entries should be per net namespace nfsd: Support the server resetting the boot verifier nfsd: Don't garbage collect files that might contain write errors fs/nfsd/export.c | 2 +- fs/nfsd/filecache.c | 76 +++++++++++++++++++++++++++++++++++++-------- fs/nfsd/filecache.h | 3 +- fs/nfsd/netns.h | 4 +++ fs/nfsd/nfs3xdr.c | 13 +++++--- fs/nfsd/nfs4proc.c | 14 +++------ fs/nfsd/nfsctl.c | 1 + fs/nfsd/nfssvc.c | 32 ++++++++++++++++++- 8 files changed, 115 insertions(+), 30 deletions(-) -- 2.21.0
