| Message ID | 20121029125914.506eb0fc@notabene.brown (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Oct 28, 2012, at 9:59 PM, NeilBrown <neilb@suse.de> wrote: > On Sun, 28 Oct 2012 21:03:45 -0400 Chuck Lever <chuck.lever@oracle.com> wrote: > >> Hi Neil- >> >> To use the legacy DNS resolver for resolving hostnames in NFSv4 referrals, I've installed the /sbin/nfs_cache_getent script on my NFS client "degas." I've confirmed it works with a 2.6.36 kernel. >> >> However, since 2.6.37 commit c5b29f885afe890f953f7f23424045cdad31d3e4 "sunrpc: use seconds since boot in expiry cache" the legacy DNS resolver appears not to work. When attempting to follow a referral that uses a server hostname, the client fails 100% of the time to mount the referred to server with an error such as: >> >> [cel@degas example.net]$ ls home >> ls: cannot open directory home: No such file or directory >> >> The contents of the dns_resolve cache appear to indicate that there are resolution results in the cache, but the CACHE_VALID flag is not set for that entry: >> >> [root@degas dns_resolve]# cat content >> # ip address hostname ttl >> # , klimt.example.net 48 >> >> klimt.example.net is the hostname that is contained in the referral. >> >> I have a second referral called "ip-address" in the same directory (domainroot), with the same content except the IP address of klimt is used instead of its hostname. Following that second referral always works. >> >> I've tried every stable.0 release up to 3.6.0, and the behavior is roughly the same for each, which suggests that there is no upstream fix for this issue thus far. >> >> Since I've never seen a problem like this reported, I'm wondering if anyone else can confirm this issue. >> >> I have a narrow interest in fixing the legacy DNS server in stable kernels, but there may also be a latent problem with the RPC cache implementation that could spell trouble for other consumers, even post-3.6. >> >> A rough outline of how you might reproduce this: >> >> + Build and install a 2.6.37 or later kernel for your NFS client with CONFIG_NFS_USE_LEGACY_DNS=y. >> >> + Set up an NFS server with "refer=" exports. man exports(5) >> >> + On your client, mount the server directory that contains the exports, then try to "cd" through one of the referrals. >> >> If you don't feel up to replicating the above arrangement, can you suggest cache debugging instrumentation that can be added to my client to help nail this? Thanks for any advice! >> > > > Hi Chuck, > looks like I messed up. > Every other cache uses absolute timestamps for expiry time. The dns resolver > differs from this and uses relative time stamps (ttl). I obviously didn't > understand this properly when I wrote the patch that broke things. > In particular, using get_expiry() is inappropriate in this context. > > Something like this should fix it. I built a 3.7-rc2 kernel with CONFIG_NFS_USE_LEGACY_DNS=y. Without your patch, following a referral containing a hostname does not work on this kernel. After applying your patch, following the same referral works as expected. Tested-by: Chuck Lever <chuck.lever@oracle.com> IMO, this fix should go to all stable kernels => 2.6.37, and to 3.7-rc. Good news is that this problem does not affect other RPC cache consumers. Thanks for the quick response! > NeilBrown > > > diff --git a/fs/nfs/dns_resolve.c b/fs/nfs/dns_resolve.c > index 31c26c4..d9415a2 100644 > --- a/fs/nfs/dns_resolve.c > +++ b/fs/nfs/dns_resolve.c > @@ -217,7 +217,7 @@ static int nfs_dns_parse(struct cache_detail *cd, char *buf, int buflen) > { > char buf1[NFS_DNS_HOSTNAME_MAXLEN+1]; > struct nfs_dns_ent key, *item; > - unsigned long ttl; > + unsigned int ttl; > ssize_t len; > int ret = -EINVAL; > > @@ -240,7 +240,8 @@ static int nfs_dns_parse(struct cache_detail *cd, char *buf, int buflen) > key.namelen = len; > memset(&key.h, 0, sizeof(key.h)); > > - ttl = get_expiry(&buf); > + if (get_int(&buf, &ttl) < 0) > + goto out; > if (ttl == 0) > goto out; > key.h.expiry_time = ttl + seconds_since_boot(); > >
diff --git a/fs/nfs/dns_resolve.c b/fs/nfs/dns_resolve.c index 31c26c4..d9415a2 100644 --- a/fs/nfs/dns_resolve.c +++ b/fs/nfs/dns_resolve.c @@ -217,7 +217,7 @@ static int nfs_dns_parse(struct cache_detail *cd, char *buf, int buflen) { char buf1[NFS_DNS_HOSTNAME_MAXLEN+1]; struct nfs_dns_ent key, *item; - unsigned long ttl; + unsigned int ttl; ssize_t len; int ret = -EINVAL; @@ -240,7 +240,8 @@ static int nfs_dns_parse(struct cache_detail *cd, char *buf, int buflen) key.namelen = len; memset(&key.h, 0, sizeof(key.h)); - ttl = get_expiry(&buf); + if (get_int(&buf, &ttl) < 0) + goto out; if (ttl == 0) goto out; key.h.expiry_time = ttl + seconds_since_boot();