On Mon, Aug 26, 2019 at 12:50:18PM -0400, Trond Myklebust wrote: > 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. These were lost before the file caching patches as well, right? Or is there some regression? > 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. Sounds sensible to me. > 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). I'm confused by the "probably should". So that's future work? I guess it'd mean some additional work to identify that case. You can't really even distinguish clients in the NFSv3 case, but I suppose you could use IP address or TCP connection as an approximation. --b. > 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
