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    SubjectRe: [RFC][PATCH] sunrpc: fix oops in rpc_create() when the mount namespace is unshared
    Quoting Cedric Le Goater (clg@fr.ibm.com):
    > On a system with nfs mounts, if a task unshares its mount namespace,
    > a oops can occur when the system is rebooted if the task is the last
    > to unreference the nfs mount. It will try to create a rpc request
    > using utsname() which has been invalidated by free_nsproxy().
    >
    > The patch fixes the issue by using the global init_utsname() but at
    > the same time, it breaks the capability of identifying rpc clients
    > per uts namespace.
    >
    > Any better suggestions ?
    >
    > BUG: unable to handle kernel NULL pointer dereference at 00000004
    > IP: [<c024c9ab>] rpc_create+0x332/0x42f
    > Oops: 0000 [#1] DEBUG_PAGEALLOC
    >
    > Pid: 1857, comm: uts-oops Not tainted (2.6.27-rc5-00319-g7686ad5 #4)
    > EIP: 0060:[<c024c9ab>] EFLAGS: 00210287 CPU: 0
    > EIP is at rpc_create+0x332/0x42f
    > EAX: 00000000 EBX: df26adf0 ECX: c0251887 EDX: 00000001
    > ESI: df26ae58 EDI: c02f293c EBP: dda0fc9c ESP: dda0fc2c
    > DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068
    > Process uts-oops (pid: 1857, ti=dda0e000 task=dd9a0778 task.ti=dda0e000)
    > Stack: c0104532 dda0fffc dda0fcac dda0e000 dda0e000 dd93b7f0 00000009 c02f2880
    > df26aefc dda0fc68 c01096b7 00000000 c0266ee0 c039a070 c039a070 dda0fc74
    > c012ca67 c039a064 dda0fc8c c012cb20 c03daf74 00000011 00000000 c0275c90
    > Call Trace:
    > [<c0104532>] ? dump_trace+0xc2/0xe2
    > [<c01096b7>] ? save_stack_trace+0x1c/0x3a
    > [<c012ca67>] ? save_trace+0x37/0x8c
    > [<c012cb20>] ? add_lock_to_list+0x64/0x96
    > [<c0256fc4>] ? rpcb_register_call+0x62/0xbb
    > [<c02570c8>] ? rpcb_register+0xab/0xb3
    > [<c0252f4d>] ? svc_register+0xb4/0x128
    > [<c0253114>] ? svc_destroy+0xec/0x103
    > [<c02531b2>] ? svc_exit_thread+0x87/0x8d
    > [<c01a75cd>] ? lockd_down+0x61/0x81
    > [<c01a577b>] ? nlmclnt_done+0xd/0xf
    > [<c01941fe>] ? nfs_destroy_server+0x14/0x16
    > [<c0194328>] ? nfs_free_server+0x4c/0xaa
    > [<c019a066>] ? nfs_kill_super+0x23/0x27
    > [<c0158585>] ? deactivate_super+0x3f/0x51
    > [<c01695d1>] ? mntput_no_expire+0x95/0xb4
    > [<c016965b>] ? release_mounts+0x6b/0x7a
    > [<c01696cc>] ? __put_mnt_ns+0x62/0x70
    > [<c0127501>] ? free_nsproxy+0x25/0x80
    > [<c012759a>] ? switch_task_namespaces+0x3e/0x43
    > [<c01275a9>] ? exit_task_namespaces+0xa/0xc
    > [<c0117fed>] ? do_exit+0x4fd/0x666
    > [<c01181b3>] ? do_group_exit+0x5d/0x83
    > [<c011fa8c>] ? get_signal_to_deliver+0x2c8/0x2e0
    > [<c0102630>] ? do_notify_resume+0x69/0x700
    > [<c011d85a>] ? do_sigaction+0x134/0x145
    > [<c0127205>] ? hrtimer_nanosleep+0x8f/0xce
    > [<c0126d1a>] ? hrtimer_wakeup+0x0/0x1c
    > [<c0103488>] ? work_notifysig+0x13/0x1b
    > =======================
    > Code: 70 20 68 cb c1 2c c0 e8 75 4e 01 00 8b 83 ac 00 00 00 59 3d 00 f0 ff ff 5f 77 63 eb 57 a1 00 80 2d c0 8b 80 a8 02 00 00 8d 73 68 <8b> 40 04 83 c0 45 e8 41 46 f7 ff ba 20 00 00 00 83 f8 21 0f 4c
    > EIP: [<c024c9ab>] rpc_create+0x332/0x42f SS:ESP 0068:dda0fc2c
    >
    > Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>

    Thanks, Cedric. Eric is probably right about the long-term fix, but
    yeah it might take a while to properly wade through the sunrpc and nfs
    layers to store the nodename at nfs mount time, and in the meantime this
    fixes a real oops.

    Acked-by: Serge Hallyn <serue@us.ibm.com>

    > ---
    > net/sunrpc/clnt.c | 4 ++--
    > 1 files changed, 2 insertions(+), 2 deletions(-)
    >
    > diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
    > index 76739e9..a59cdf4 100644
    > --- a/net/sunrpc/clnt.c
    > +++ b/net/sunrpc/clnt.c
    > @@ -213,10 +213,10 @@ static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, stru
    > }
    >
    > /* save the nodename */
    > - clnt->cl_nodelen = strlen(utsname()->nodename);
    > + clnt->cl_nodelen = strlen(init_utsname()->nodename);
    > if (clnt->cl_nodelen > UNX_MAXNODENAME)
    > clnt->cl_nodelen = UNX_MAXNODENAME;
    > - memcpy(clnt->cl_nodename, utsname()->nodename, clnt->cl_nodelen);
    > + memcpy(clnt->cl_nodename, init_utsname()->nodename, clnt->cl_nodelen);
    > rpc_register_client(clnt);
    > return clnt;
    >
    > --
    > 1.5.5.1


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