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    SubjectRe: NFS crash in un-modified 3.0.0-rc3+, list corruption.
    On Mon, Jun 20, 2011 at 04:26:48PM -0700, Ben Greear wrote:
    > On 06/20/2011 03:42 PM, Ben Greear wrote:
    > >This machine is acting as a server. It is from linux-2.6, pulled
    > >today:
    > >
    > >commit de505e709ffb09a7382ca8e0d8c7dbb171ba5830
    > >
    > >We are hitting it with 200 clients reading and writing, mounting and
    > >un-mounting.
    > >This bug is fairly reproducible (twice today).
    > >
    > >Large amounts of debugging options are enabled.
    > We were also starting/stopping NFS on the server machine.
    > It appears that this crash happens during the
    > /etc/init.d/nfs stop
    > command.

    I'll be submitting the below.

    The bug's been there for a really long time and we're getting late into
    the release cycle so I'll probably just save it for 3.1 (but it'll go to
    stable as well then).


    commit 0f4bb2521a0e300443e9d80b10778f5a93cc0dbc
    Author: J. Bruce Fields <>
    Date: Wed Jun 29 16:49:04 2011 -0400

    svcrpc: fix list-corrupting race on nfsd shutdown

    After commit 3262c816a3d7fb1eaabce633caa317887ed549ae "[PATCH] knfsd:
    split svc_serv into pools", svc_delete_xprt (then svc_delete_socket) no
    longer removed its xpt_ready (then sk_ready) field from whatever list it
    was on, noting that there was no point since the whole list was about to
    be destroyed anyway.

    That was mostly true, but forgot that a few svc_xprt_enqueue()'s might
    still be hanging around playing with the about-to-be-destroyed list, and
    could get themselves into trouble writing to freed memory if we left
    this xprt on the list after freeing it.

    (This is actually functionally identical to a patch made first by Ben
    Greear, but with more comments.)

    Reported-by: Ben Greear <>
    Tested-by: Ben Greear <>
    Signed-off-by: J. Bruce Fields <>

    diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
    index ab86b79..bd31208 100644
    --- a/net/sunrpc/svc_xprt.c
    +++ b/net/sunrpc/svc_xprt.c
    @@ -902,12 +902,13 @@ void svc_delete_xprt(struct svc_xprt *xprt)
    if (!test_and_set_bit(XPT_DETACHED, &xprt->xpt_flags))
    - * We used to delete the transport from whichever list
    - * it's sk_xprt.xpt_ready node was on, but we don't actually
    - * need to. This is because the only time we're called
    - * while still attached to a queue, the queue itself
    - * is about to be destroyed (in svc_destroy).
    + * The only time we're called while xpt_ready is still on a list
    + * is while the list itself is about to be destroyed (in
    + * svc_destroy). BUT svc_xprt_enqueue could still be attempting
    + * to add new entries to the sp_sockets list, so we can't leave
    + * a freed xprt on it.
    + list_del_init(&xprt->xpt_ready);
    if (test_bit(XPT_TEMP, &xprt->xpt_flags))

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