From: Rajasi Mandal Date: Fri, 5 Dec 2025 20:11:51 +0000 (+0000) Subject: cifs: client: allow changing multichannel mount options on remount X-Git-Tag: v6.19-rc1~47^2~10 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=ef529f655a2c9f06b4d1cb8f2b3e577c7f6f7012;p=thirdparty%2Fkernel%2Flinux.git cifs: client: allow changing multichannel mount options on remount Previously, the client did not update a session's channel state when multichannel or max_channels mount options were changed via remount. This led to inconsistent behavior and prevented enabling or disabling multichannel support without a full unmount/remount cycle. Enable dynamic reconfiguration of multichannel and max_channels during remount by: - Introducing smb3_sync_ses_chan_max(), a centralized function for channel updates which synchronizes the session's channels with the updated configuration. - Replacing cifs_disable_secondary_channels() with cifs_decrease_secondary_channels(), which accepts a disable_mchan flag to support multichannel disable when the server stops supporting multichannel. - Updating remount logic to detect changes in multichannel or max_channels and trigger appropriate session/channel updates. Current limitation: - The query_interfaces worker runs even when max_channels=1 so that multichannel can be enabled later via remount without requiring an unmount. This is a temporary approach and may be refined in the future. Users can safely modify multichannel and max_channels on an existing mount. The client will correctly adjust the session's channel state to match the new configuration, preserving durability where possible and avoiding unnecessary disconnects. Reviewed-by: Shyam Prasad N Signed-off-by: Rajasi Mandal Signed-off-by: Steve French --- diff --git a/fs/smb/client/cifsproto.h b/fs/smb/client/cifsproto.h index 823ca4f369140..bbe07e6018c0f 100644 --- a/fs/smb/client/cifsproto.h +++ b/fs/smb/client/cifsproto.h @@ -635,6 +635,8 @@ int cifs_alloc_hash(const char *name, struct shash_desc **sdesc); void cifs_free_hash(struct shash_desc **sdesc); int cifs_try_adding_channels(struct cifs_ses *ses); +int smb3_update_ses_channels(struct cifs_ses *ses, struct TCP_Server_Info *server, + bool from_reconnect, bool disable_mchan); bool is_ses_using_iface(struct cifs_ses *ses, struct cifs_server_iface *iface); void cifs_ses_mark_for_reconnect(struct cifs_ses *ses); @@ -660,7 +662,7 @@ bool cifs_chan_is_iface_active(struct cifs_ses *ses, struct TCP_Server_Info *server); void -cifs_disable_secondary_channels(struct cifs_ses *ses); +cifs_decrease_secondary_channels(struct cifs_ses *ses, bool disable_mchan); void cifs_chan_update_iface(struct cifs_ses *ses, struct TCP_Server_Info *server); int diff --git a/fs/smb/client/connect.c b/fs/smb/client/connect.c index 2f184e9d3c67c..cca6c722598d6 100644 --- a/fs/smb/client/connect.c +++ b/fs/smb/client/connect.c @@ -3926,7 +3926,9 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb3_fs_context *ctx) ctx->prepath = NULL; out: - cifs_try_adding_channels(mnt_ctx.ses); + smb3_update_ses_channels(mnt_ctx.ses, mnt_ctx.server, + false /* from_reconnect */, + false /* disable_mchan */); rc = mount_setup_tlink(cifs_sb, mnt_ctx.ses, mnt_ctx.tcon); if (rc) goto error; diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c index 1419a7336d3fe..c2de97e4ad59d 100644 --- a/fs/smb/client/fs_context.c +++ b/fs/smb/client/fs_context.c @@ -758,6 +758,7 @@ static int smb3_fs_context_parse_param(struct fs_context *fc, static int smb3_fs_context_parse_monolithic(struct fs_context *fc, void *data); static int smb3_get_tree(struct fs_context *fc); +static void smb3_sync_ses_chan_max(struct cifs_ses *ses, unsigned int max_channels); static int smb3_reconfigure(struct fs_context *fc); static const struct fs_context_operations smb3_fs_context_ops = { @@ -1055,6 +1056,22 @@ int smb3_sync_session_ctx_passwords(struct cifs_sb_info *cifs_sb, struct cifs_se return 0; } +/* + * smb3_sync_ses_chan_max - Synchronize the session's maximum channel count + * @ses: pointer to the old CIFS session structure + * @max_channels: new maximum number of channels to allow + * + * Updates the session's chan_max field to the new value, protecting the update + * with the session's channel lock. This should be called whenever the maximum + * allowed channels for a session changes (e.g., after a remount or reconfigure). + */ +static void smb3_sync_ses_chan_max(struct cifs_ses *ses, unsigned int max_channels) +{ + spin_lock(&ses->chan_lock); + ses->chan_max = max_channels; + spin_unlock(&ses->chan_lock); +} + static int smb3_reconfigure(struct fs_context *fc) { struct smb3_fs_context *ctx = smb3_fc2context(fc); @@ -1137,7 +1154,39 @@ static int smb3_reconfigure(struct fs_context *fc) ses->password2 = new_password2; } - mutex_unlock(&ses->session_mutex); + /* + * If multichannel or max_channels has changed, update the session's channels accordingly. + * This may add or remove channels to match the new configuration. + */ + if ((ctx->multichannel != cifs_sb->ctx->multichannel) || + (ctx->max_channels != cifs_sb->ctx->max_channels)) { + + /* Synchronize ses->chan_max with the new mount context */ + smb3_sync_ses_chan_max(ses, ctx->max_channels); + /* Now update the session's channels to match the new configuration */ + /* Prevent concurrent scaling operations */ + spin_lock(&ses->ses_lock); + if (ses->flags & CIFS_SES_FLAG_SCALE_CHANNELS) { + spin_unlock(&ses->ses_lock); + mutex_unlock(&ses->session_mutex); + return -EINVAL; + } + ses->flags |= CIFS_SES_FLAG_SCALE_CHANNELS; + spin_unlock(&ses->ses_lock); + + mutex_unlock(&ses->session_mutex); + + rc = smb3_update_ses_channels(ses, ses->server, + false /* from_reconnect */, + false /* disable_mchan */); + + /* Clear scaling flag after operation */ + spin_lock(&ses->ses_lock); + ses->flags &= ~CIFS_SES_FLAG_SCALE_CHANNELS; + spin_unlock(&ses->ses_lock); + } else { + mutex_unlock(&ses->session_mutex); + } STEAL_STRING(cifs_sb, ctx, domainname); STEAL_STRING(cifs_sb, ctx, nodename); diff --git a/fs/smb/client/sess.c b/fs/smb/client/sess.c index 3e39faf637861..a72d6a6d20f08 100644 --- a/fs/smb/client/sess.c +++ b/fs/smb/client/sess.c @@ -265,12 +265,16 @@ int cifs_try_adding_channels(struct cifs_ses *ses) } /* - * called when multichannel is disabled by the server. - * this always gets called from smb2_reconnect - * and cannot get called in parallel threads. + * cifs_decrease_secondary_channels - Reduce the number of active secondary channels + * @ses: pointer to the CIFS session structure + * @disable_mchan: if true, reduce to a single channel; if false, reduce to chan_max + * + * This function disables and cleans up extra secondary channels for a CIFS session. + * If called during reconfiguration, it reduces the channel count to the new maximum (chan_max). + * Otherwise, it disables all but the primary channel. */ void -cifs_disable_secondary_channels(struct cifs_ses *ses) +cifs_decrease_secondary_channels(struct cifs_ses *ses, bool disable_mchan) { int i, chan_count; struct TCP_Server_Info *server; @@ -281,12 +285,16 @@ cifs_disable_secondary_channels(struct cifs_ses *ses) if (chan_count == 1) goto done; - ses->chan_count = 1; - - /* for all secondary channels reset the need reconnect bit */ - ses->chans_need_reconnect &= 1; + /* Update the chan_count to the new maximum */ + if (disable_mchan) { + cifs_dbg(FYI, "server does not support multichannel anymore.\n"); + ses->chan_count = 1; + } else { + ses->chan_count = ses->chan_max; + } - for (i = 1; i < chan_count; i++) { + /* Disable all secondary channels beyond the new chan_count */ + for (i = ses->chan_count ; i < chan_count; i++) { iface = ses->chans[i].iface; server = ses->chans[i].server; @@ -318,6 +326,15 @@ cifs_disable_secondary_channels(struct cifs_ses *ses) spin_lock(&ses->chan_lock); } + /* For extra secondary channels, reset the need reconnect bit */ + if (ses->chan_count == 1) { + cifs_dbg(VFS, "Disable all secondary channels\n"); + ses->chans_need_reconnect &= 1; + } else { + cifs_dbg(VFS, "Disable extra secondary channels\n"); + ses->chans_need_reconnect &= ((1UL << ses->chan_max) - 1); + } + done: spin_unlock(&ses->chan_lock); } diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c index bff39a5f39b0f..e8b423a28e18c 100644 --- a/fs/smb/client/smb2pdu.c +++ b/fs/smb/client/smb2pdu.c @@ -168,7 +168,7 @@ out: static int cifs_chan_skip_or_disable(struct cifs_ses *ses, struct TCP_Server_Info *server, - bool from_reconnect) + bool from_reconnect, bool disable_mchan) { struct TCP_Server_Info *pserver; unsigned int chan_index; @@ -206,14 +206,46 @@ skip_terminate: return -EHOSTDOWN; } - cifs_server_dbg(VFS, - "server does not support multichannel anymore. Disable all other channels\n"); - cifs_disable_secondary_channels(ses); - + cifs_decrease_secondary_channels(ses, disable_mchan); return 0; } +/* + * smb3_update_ses_channels - Synchronize session channels with new configuration + * @ses: pointer to the CIFS session structure + * @server: pointer to the TCP server info structure + * @from_reconnect: indicates if called from reconnect context + * @disable_mchan: indicates if called from reconnect to disable multichannel + * + * Returns 0 on success or error code on failure. + * + * Outside of reconfigure, this function is called from cifs_mount() during mount + * and from reconnect scenarios to adjust channel count when the + * server's multichannel support changes. + */ +int smb3_update_ses_channels(struct cifs_ses *ses, struct TCP_Server_Info *server, + bool from_reconnect, bool disable_mchan) +{ + int rc = 0; + /* + * Manage session channels based on current count vs max: + * - If disable requested, skip or disable the channel + * - If below max channels, attempt to add more + * - If above max channels, skip or disable excess channels + */ + if (disable_mchan) + rc = cifs_chan_skip_or_disable(ses, server, from_reconnect, disable_mchan); + else { + if (ses->chan_count < ses->chan_max) + rc = cifs_try_adding_channels(ses); + else if (ses->chan_count > ses->chan_max) + rc = cifs_chan_skip_or_disable(ses, server, from_reconnect, disable_mchan); + } + + return rc; +} + static int smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon, struct TCP_Server_Info *server, bool from_reconnect) @@ -355,8 +387,8 @@ again: */ if (ses->chan_count > 1 && !(server->capabilities & SMB2_GLOBAL_CAP_MULTI_CHANNEL)) { - rc = cifs_chan_skip_or_disable(ses, server, - from_reconnect); + rc = smb3_update_ses_channels(ses, server, + from_reconnect, true /* disable_mchan */); if (rc) { mutex_unlock(&ses->session_mutex); goto out; @@ -438,8 +470,9 @@ skip_sess_setup: * treat this as server not supporting multichannel */ - rc = cifs_chan_skip_or_disable(ses, server, - from_reconnect); + rc = smb3_update_ses_channels(ses, server, + from_reconnect, + true /* disable_mchan */); goto skip_add_channels; } else if (rc) cifs_tcon_dbg(FYI, "%s: failed to query server interfaces: %d\n", @@ -451,7 +484,8 @@ skip_sess_setup: if (ses->chan_count == 1) cifs_server_dbg(VFS, "supports multichannel now\n"); - cifs_try_adding_channels(ses); + smb3_update_ses_channels(ses, server, from_reconnect, + false /* disable_mchan */); } } else { mutex_unlock(&ses->session_mutex); @@ -1105,8 +1139,7 @@ SMB2_negotiate(const unsigned int xid, req->SecurityMode = 0; req->Capabilities = cpu_to_le32(server->vals->req_capabilities); - if (ses->chan_max > 1) - req->Capabilities |= cpu_to_le32(SMB2_GLOBAL_CAP_MULTI_CHANNEL); + req->Capabilities |= cpu_to_le32(SMB2_GLOBAL_CAP_MULTI_CHANNEL); /* ClientGUID must be zero for SMB2.02 dialect */ if (server->vals->protocol_id == SMB20_PROT_ID) @@ -1332,8 +1365,7 @@ int smb3_validate_negotiate(const unsigned int xid, struct cifs_tcon *tcon) pneg_inbuf->Capabilities = cpu_to_le32(server->vals->req_capabilities); - if (tcon->ses->chan_max > 1) - pneg_inbuf->Capabilities |= cpu_to_le32(SMB2_GLOBAL_CAP_MULTI_CHANNEL); + pneg_inbuf->Capabilities |= cpu_to_le32(SMB2_GLOBAL_CAP_MULTI_CHANNEL); memcpy(pneg_inbuf->Guid, server->client_guid, SMB2_CLIENT_GUID_SIZE);