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    SubjectRe: [PATCH] nfs: fix bdi_unregister() before sb kill
    On Fri, Sep 18 2009, Jens Axboe wrote:
    > On Fri, Sep 18 2009, Trond Myklebust wrote:
    > > On Fri, 2009-09-18 at 17:02 +0200, Jens Axboe wrote:
    > > > On Fri, Sep 18 2009, Jens Axboe wrote:
    > > > > On Thu, Sep 17 2009, Trond Myklebust wrote:
    > > > > > On Thu, 2009-09-17 at 21:40 +0200, Jens Axboe wrote:
    > > > > > > On Thu, Sep 17 2009, Jens Axboe wrote:
    > > > > > > > Hi,
    > > > > > > >
    > > > > > > > This can cause a hang on NFS umount, since the bdi gets pruned before we
    > > > > > > > flush any pending dirty IO. Peter, can you check whether it fixes your
    > > > > > > > issue?
    > > > > > >
    > > > > > > There's another problem with NFS && backing devices. NFS may call
    > > > > > > bdi_destroy() on a bdi without ever called bdi_init(). This was always a
    > > > > > > bad idea, now it's an issue.
    > > > > > >
    > > > > > > So, Trond, can I safely add a server->flags private flag to indicate
    > > > > > > that we have called bdi_init()? Then nfs_free_server() knows when to
    > > > > > > call bdi_destroy(). Seems like the safest fix, since error handling is
    > > > > > > currently 'just call nfs_free_server()'.
    > > > > >
    > > > > > Urgh... Is there any reason why we can't just move the call to
    > > > > > bdi_init() into nfs_bdi_register()? It seems bizarre to have to
    > > > > > initialise the backing_dev_info twice like this...
    > > > >
    > > > > No reason at all, I don't know why it was implemented that way
    > > > > originally.
    > > > >
    > > > > > If we do that, then we can just look at the BDI_registered state flag in
    > > > > > order to figure out if we need to call bdi_unregister()
    > > > >
    > > > > That's not exactly pretty either, diving into internal bdi details to
    > > > > find out if we did an init/register of the device. BDI_registered is
    > > > > just a debug flag, it may even go away again shortly.
    > > >
    > > > Trond, we need to make some sort of decision on this very shortly. It
    > > > definitely needs to be fixed for -rc1, it's causing NFS oopses. So lets
    > > > make some sort of call on this and get it added, then you/we/I can
    > > > always pretty it up later.
    > > >
    > >
    > > OK... I think the solution is to move the call to bdi_init() into
    > > nfs_bdi_register(), then move the calls to nfs_bdi_register() into
    > > nfs_set_super() (with an appropriate call to bdi_destroy() if
    > > set_anon_super() fails).
    > >
    > > Then we can put bdi_destroy() in place of the call to bdi_unregister()
    > > in nfs_kill_super().
    >
    > Yeah, that sounds cleaner.
    >
    > > I'm not going to attempt a patch, since I don't have a copy of your
    > > current tree to base it on, but does the above make sense to you?
    >
    > My current tree in the NFS area is just a one liner to move the
    > bdi_destroy() in nfs_kill_super(). I'll try and cut a patch later
    > tonight.

    How does this look? It compiles, but I cannot test before sunday. It
    would be great if you (or someone else) could :-). Peter, if you have
    the time, it would be nice if you could check whether this one works for
    you too.

    diffstat is tasty, too:

    client.c | 4 ----
    super.c | 53 ++++++++++++++++++++++++++---------------------------
    2 files changed, 26 insertions(+), 31 deletions(-)


    diff --git a/fs/nfs/client.c b/fs/nfs/client.c
    index e350bd6..bb93060 100644
    --- a/fs/nfs/client.c
    +++ b/fs/nfs/client.c
    @@ -933,10 +933,6 @@ static int nfs_probe_fsinfo(struct nfs_server *server, struct nfs_fh *mntfh, str
    goto out_error;

    nfs_server_set_fsinfo(server, &fsinfo);
    - error = bdi_init(&server->backing_dev_info);
    - if (error)
    - goto out_error;
    -

    /* Get some general file system info */
    if (server->namelen == 0) {
    diff --git a/fs/nfs/super.c b/fs/nfs/super.c
    index f1cc058..712950d 100644
    --- a/fs/nfs/super.c
    +++ b/fs/nfs/super.c
    @@ -2008,17 +2008,41 @@ struct nfs_sb_mountdata {
    int mntflags;
    };

    +static int nfs_bdi_register(struct nfs_server *server)
    +{
    + struct backing_dev_info *bdi = &server->backing_dev_info;
    + int err;
    +
    + err = bdi_init(bdi);
    + if (!err) {
    + err = bdi_register_dev(bdi, server->s_dev);
    + if (!err)
    + return 0;
    + }
    +
    + bdi_destroy(bdi);
    + return err;
    +}
    +
    static int nfs_set_super(struct super_block *s, void *data)
    {
    struct nfs_sb_mountdata *sb_mntdata = data;
    struct nfs_server *server = sb_mntdata->server;
    int ret;

    + ret = nfs_bdi_register(server);
    + if (ret)
    + return ret;
    +
    s->s_flags = sb_mntdata->mntflags;
    s->s_fs_info = server;
    ret = set_anon_super(s, server);
    - if (ret == 0)
    + if (ret == 0) {
    server->s_dev = s->s_dev;
    + return 0;
    + }
    +
    + bdi_destroy(&server->backing_dev_info);
    return ret;
    }

    @@ -2075,11 +2099,6 @@ static int nfs_compare_super(struct super_block *sb, void *data)
    return nfs_compare_mount_options(sb, server, mntflags);
    }

    -static int nfs_bdi_register(struct nfs_server *server)
    -{
    - return bdi_register_dev(&server->backing_dev_info, server->s_dev);
    -}
    -
    static int nfs_get_sb(struct file_system_type *fs_type,
    int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt)
    {
    @@ -2135,10 +2154,6 @@ static int nfs_get_sb(struct file_system_type *fs_type,
    if (s->s_fs_info != server) {
    nfs_free_server(server);
    server = NULL;
    - } else {
    - error = nfs_bdi_register(server);
    - if (error)
    - goto error_splat_super;
    }

    if (!s->s_root) {
    @@ -2191,7 +2206,7 @@ static void nfs_kill_super(struct super_block *s)
    struct nfs_server *server = NFS_SB(s);

    kill_anon_super(s);
    - bdi_unregister(&server->backing_dev_info);
    + bdi_destroy(&server->backing_dev_info);
    nfs_fscache_release_super_cookie(s);
    nfs_free_server(server);
    }
    @@ -2236,10 +2251,6 @@ static int nfs_xdev_get_sb(struct file_system_type *fs_type, int flags,
    if (s->s_fs_info != server) {
    nfs_free_server(server);
    server = NULL;
    - } else {
    - error = nfs_bdi_register(server);
    - if (error)
    - goto error_splat_super;
    }

    if (!s->s_root) {
    @@ -2499,10 +2510,6 @@ static int nfs4_remote_get_sb(struct file_system_type *fs_type,
    if (s->s_fs_info != server) {
    nfs_free_server(server);
    server = NULL;
    - } else {
    - error = nfs_bdi_register(server);
    - if (error)
    - goto error_splat_super;
    }

    if (!s->s_root) {
    @@ -2732,10 +2739,6 @@ static int nfs4_xdev_get_sb(struct file_system_type *fs_type, int flags,
    if (s->s_fs_info != server) {
    nfs_free_server(server);
    server = NULL;
    - } else {
    - error = nfs_bdi_register(server);
    - if (error)
    - goto error_splat_super;
    }

    if (!s->s_root) {
    @@ -2813,10 +2816,6 @@ static int nfs4_remote_referral_get_sb(struct file_system_type *fs_type,
    if (s->s_fs_info != server) {
    nfs_free_server(server);
    server = NULL;
    - } else {
    - error = nfs_bdi_register(server);
    - if (error)
    - goto error_splat_super;
    }

    if (!s->s_root) {
    --
    Jens Axboe



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