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    Subject[PATCH AUTOSEL 5.6 63/79] cifs: do not share tcons with DFS
    Date
    From: Paulo Alcantara <pc@cjr.nz>

    [ Upstream commit 65303de829dd6d291a4947c1a31de31896f8a060 ]

    This disables tcon re-use for DFS shares.

    tcon->dfs_path stores the path that the tcon should connect to when
    doing failing over.

    If that tcon is used multiple times e.g. 2 mounts using it with
    different prefixpath, each will need a different dfs_path but there is
    only one tcon. The other solution would be to split the tcon in 2
    tcons during failover but that is much harder.

    tcons could not be shared with DFS in cifs.ko because in a
    DFS namespace like:

    //domain/dfsroot -> /serverA/dfsroot, /serverB/dfsroot

    //serverA/dfsroot/link -> /serverA/target1/aa/bb

    //serverA/dfsroot/link2 -> /serverA/target1/cc/dd

    you can see that link and link2 are two DFS links that both resolve to
    the same target share (/serverA/target1), so cifs.ko will only contain a
    single tcon for both link and link2.

    The problem with that is, if we (auto)mount "link" and "link2", cifs.ko
    will only contain a single tcon for both DFS links so we couldn't
    perform failover or refresh the DFS cache for both links because
    tcon->dfs_path was set to either "link" or "link2", but not both --
    which is wrong.

    Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
    Reviewed-by: Aurelien Aptel <aaptel@suse.com>
    Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
    Signed-off-by: Steve French <stfrench@microsoft.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/cifs/connect.c | 4 ++++
    1 file changed, 4 insertions(+)

    diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
    index d4a23b48e24d8..9c614d6916c2d 100644
    --- a/fs/cifs/connect.c
    +++ b/fs/cifs/connect.c
    @@ -3419,6 +3419,10 @@ cifs_find_tcon(struct cifs_ses *ses, struct smb_vol *volume_info)
    spin_lock(&cifs_tcp_ses_lock);
    list_for_each(tmp, &ses->tcon_list) {
    tcon = list_entry(tmp, struct cifs_tcon, tcon_list);
    +#ifdef CONFIG_CIFS_DFS_UPCALL
    + if (tcon->dfs_path)
    + continue;
    +#endif
    if (!match_tcon(tcon, volume_info))
    continue;
    ++tcon->tc_count;
    --
    2.20.1
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