Re: [PATCH v2 2/2] cifs: prevent data race in cifs_reconnect_tcon()

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updated cifs-2.6.git for-next with these two patches

On Tue, Feb 28, 2023 at 4:02 PM Paulo Alcantara <pc@xxxxxxxxxxxxx> wrote:
>
> Make sure to get an up-to-date TCP_Server_Info::nr_targets value prior
> to waiting the server to be reconnected in cifs_reconnect_tcon().  It
> is set in cifs_tcp_ses_needs_reconnect() and protected by
> TCP_Server_Info::srv_lock.
>
> Create a new cifs_wait_for_server_reconnect() helper that can be used
> by both SMB2+ and CIFS reconnect code.
>
> Signed-off-by: Paulo Alcantara (SUSE) <pc@xxxxxxxxxxxxx>
> ---
> v1 -> v2: fixed double unlock pointed out by Steve
>
>  fs/cifs/cifsproto.h |  1 +
>  fs/cifs/cifssmb.c   | 43 ++----------------------
>  fs/cifs/misc.c      | 44 ++++++++++++++++++++++++
>  fs/cifs/smb2pdu.c   | 82 ++++++++++++---------------------------------
>  4 files changed, 69 insertions(+), 101 deletions(-)
>
> diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h
> index 20a2f0f3f682..e2eff66eefab 100644
> --- a/fs/cifs/cifsproto.h
> +++ b/fs/cifs/cifsproto.h
> @@ -694,5 +694,6 @@ static inline int cifs_create_options(struct cifs_sb_info *cifs_sb, int options)
>
>  struct super_block *cifs_get_tcon_super(struct cifs_tcon *tcon);
>  void cifs_put_tcon_super(struct super_block *sb);
> +int cifs_wait_for_server_reconnect(struct TCP_Server_Info *server, bool retry);
>
>  #endif                 /* _CIFSPROTO_H */
> diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
> index a24e4ddf8043..a43c78396dd8 100644
> --- a/fs/cifs/cifssmb.c
> +++ b/fs/cifs/cifssmb.c
> @@ -72,7 +72,6 @@ cifs_reconnect_tcon(struct cifs_tcon *tcon, int smb_command)
>         struct cifs_ses *ses;
>         struct TCP_Server_Info *server;
>         struct nls_table *nls_codepage;
> -       int retries;
>
>         /*
>          * SMBs NegProt, SessSetup, uLogoff do not have tcon yet so check for
> @@ -102,45 +101,9 @@ cifs_reconnect_tcon(struct cifs_tcon *tcon, int smb_command)
>         }
>         spin_unlock(&tcon->tc_lock);
>
> -       retries = server->nr_targets;
> -
> -       /*
> -        * Give demultiplex thread up to 10 seconds to each target available for
> -        * reconnect -- should be greater than cifs socket timeout which is 7
> -        * seconds.
> -        */
> -       while (server->tcpStatus == CifsNeedReconnect) {
> -               rc = wait_event_interruptible_timeout(server->response_q,
> -                                                     (server->tcpStatus != CifsNeedReconnect),
> -                                                     10 * HZ);
> -               if (rc < 0) {
> -                       cifs_dbg(FYI, "%s: aborting reconnect due to a received signal by the process\n",
> -                                __func__);
> -                       return -ERESTARTSYS;
> -               }
> -
> -               /* are we still trying to reconnect? */
> -               spin_lock(&server->srv_lock);
> -               if (server->tcpStatus != CifsNeedReconnect) {
> -                       spin_unlock(&server->srv_lock);
> -                       break;
> -               }
> -               spin_unlock(&server->srv_lock);
> -
> -               if (retries && --retries)
> -                       continue;
> -
> -               /*
> -                * on "soft" mounts we wait once. Hard mounts keep
> -                * retrying until process is killed or server comes
> -                * back on-line
> -                */
> -               if (!tcon->retry) {
> -                       cifs_dbg(FYI, "gave up waiting on reconnect in smb_init\n");
> -                       return -EHOSTDOWN;
> -               }
> -               retries = server->nr_targets;
> -       }
> +       rc = cifs_wait_for_server_reconnect(server, tcon->retry);
> +       if (rc)
> +               return rc;
>
>         spin_lock(&ses->chan_lock);
>         if (!cifs_chan_needs_reconnect(ses, server) && !tcon->need_reconnect) {
> diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
> index 0c6c1fc8dae9..a0d286ee723d 100644
> --- a/fs/cifs/misc.c
> +++ b/fs/cifs/misc.c
> @@ -1266,3 +1266,47 @@ int cifs_inval_name_dfs_link_error(const unsigned int xid,
>         return 0;
>  }
>  #endif
> +
> +int cifs_wait_for_server_reconnect(struct TCP_Server_Info *server, bool retry)
> +{
> +       int timeout = 10;
> +       int rc;
> +
> +       spin_lock(&server->srv_lock);
> +       if (server->tcpStatus != CifsNeedReconnect) {
> +               spin_unlock(&server->srv_lock);
> +               return 0;
> +       }
> +       timeout *= server->nr_targets;
> +       spin_unlock(&server->srv_lock);
> +
> +       /*
> +        * Give demultiplex thread up to 10 seconds to each target available for
> +        * reconnect -- should be greater than cifs socket timeout which is 7
> +        * seconds.
> +        *
> +        * On "soft" mounts we wait once. Hard mounts keep retrying until
> +        * process is killed or server comes back on-line.
> +        */
> +       do {
> +               rc = wait_event_interruptible_timeout(server->response_q,
> +                                                     (server->tcpStatus != CifsNeedReconnect),
> +                                                     timeout * HZ);
> +               if (rc < 0) {
> +                       cifs_dbg(FYI, "%s: aborting reconnect due to received signal\n",
> +                                __func__);
> +                       return -ERESTARTSYS;
> +               }
> +
> +               /* are we still trying to reconnect? */
> +               spin_lock(&server->srv_lock);
> +               if (server->tcpStatus != CifsNeedReconnect) {
> +                       spin_unlock(&server->srv_lock);
> +                       return 0;
> +               }
> +               spin_unlock(&server->srv_lock);
> +       } while (retry);
> +
> +       cifs_dbg(FYI, "%s: gave up waiting on reconnect\n", __func__);
> +       return -EHOSTDOWN;
> +}
> diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
> index ca9d7110ddcb..0e53265e1462 100644
> --- a/fs/cifs/smb2pdu.c
> +++ b/fs/cifs/smb2pdu.c
> @@ -139,66 +139,6 @@ smb2_hdr_assemble(struct smb2_hdr *shdr, __le16 smb2_cmd,
>         return;
>  }
>
> -static int wait_for_server_reconnect(struct TCP_Server_Info *server,
> -                                    __le16 smb2_command, bool retry)
> -{
> -       int timeout = 10;
> -       int rc;
> -
> -       spin_lock(&server->srv_lock);
> -       if (server->tcpStatus != CifsNeedReconnect) {
> -               spin_unlock(&server->srv_lock);
> -               return 0;
> -       }
> -       timeout *= server->nr_targets;
> -       spin_unlock(&server->srv_lock);
> -
> -       /*
> -        * Return to caller for TREE_DISCONNECT and LOGOFF and CLOSE
> -        * here since they are implicitly done when session drops.
> -        */
> -       switch (smb2_command) {
> -       /*
> -        * BB Should we keep oplock break and add flush to exceptions?
> -        */
> -       case SMB2_TREE_DISCONNECT:
> -       case SMB2_CANCEL:
> -       case SMB2_CLOSE:
> -       case SMB2_OPLOCK_BREAK:
> -               return -EAGAIN;
> -       }
> -
> -       /*
> -        * Give demultiplex thread up to 10 seconds to each target available for
> -        * reconnect -- should be greater than cifs socket timeout which is 7
> -        * seconds.
> -        *
> -        * On "soft" mounts we wait once. Hard mounts keep retrying until
> -        * process is killed or server comes back on-line.
> -        */
> -       do {
> -               rc = wait_event_interruptible_timeout(server->response_q,
> -                                                     (server->tcpStatus != CifsNeedReconnect),
> -                                                     timeout * HZ);
> -               if (rc < 0) {
> -                       cifs_dbg(FYI, "%s: aborting reconnect due to received signal\n",
> -                                __func__);
> -                       return -ERESTARTSYS;
> -               }
> -
> -               /* are we still trying to reconnect? */
> -               spin_lock(&server->srv_lock);
> -               if (server->tcpStatus != CifsNeedReconnect) {
> -                       spin_unlock(&server->srv_lock);
> -                       return 0;
> -               }
> -               spin_unlock(&server->srv_lock);
> -       } while (retry);
> -
> -       cifs_dbg(FYI, "%s: gave up waiting on reconnect\n", __func__);
> -       return -EHOSTDOWN;
> -}
> -
>  static int
>  smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
>                struct TCP_Server_Info *server)
> @@ -243,7 +183,27 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
>             (!tcon->ses->server) || !server)
>                 return -EIO;
>
> -       rc = wait_for_server_reconnect(server, smb2_command, tcon->retry);
> +       spin_lock(&server->srv_lock);
> +       if (server->tcpStatus == CifsNeedReconnect) {
> +               /*
> +                * Return to caller for TREE_DISCONNECT and LOGOFF and CLOSE
> +                * here since they are implicitly done when session drops.
> +                */
> +               switch (smb2_command) {
> +               /*
> +                * BB Should we keep oplock break and add flush to exceptions?
> +                */
> +               case SMB2_TREE_DISCONNECT:
> +               case SMB2_CANCEL:
> +               case SMB2_CLOSE:
> +               case SMB2_OPLOCK_BREAK:
> +                       spin_unlock(&server->srv_lock);
> +                       return -EAGAIN;
> +               }
> +       }
> +       spin_unlock(&server->srv_lock);
> +
> +       rc = cifs_wait_for_server_reconnect(server, tcon->retry);
>         if (rc)
>                 return rc;
>
> --
> 2.39.2
>


-- 
Thanks,

Steve




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