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NFS: Retry mounting NFSROOT
commit 43717c7 upstream. Lukas Razik <firstname.lastname@example.org> reports that on his SPARC system, booting with an NFS root file system stopped working after commit 56463e5 "NFS: Use super.c for NFSROOT mount option parsing." We found that the network switch to which Lukas' client was attached was delaying access to the LAN after the client's NIC driver reported that its link was up. The delay was longer than the timeouts used in the NFS client during mounting. NFSROOT worked for Lukas before commit 56463e5 because in those kernels, the client's first operation was an rpcbind request to determine which port the NFS server was listening on. When that request failed after a long timeout, the client simply selected the default NFS port (2049). By that time the switch was allowing access to the LAN, and the mount succeeded. Neither of these client behaviors is desirable, so reverting 56463e5 is really not a choice. Instead, introduce a mechanism that retries the NFSROOT mount request several times. This is the same tactic that normal user space NFS mounts employ to overcome server and network delays. Signed-off-by: Lukas Razik <email@example.com> [ cel: match kernel coding style, add proper patch description ] [ cel: add exponential back-off ] Signed-off-by: Chuck Lever <firstname.lastname@example.org> Tested-by: Lukas Razik <email@example.com> Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com> Signed-off-by: Greg Kroah-Hartman <firstname.lastname@example.org>
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