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Mon, 17 Nov 2025 18:27:44 -0800 (PST) Received: from linuxbackup1-rm.hzz4ddxqtfeetjrh00qlbgyytb.rx.internal.cloudapp.net ([4.247.136.47]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2985c23849esm153170975ad.5.2025.11.17.18.27.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Nov 2025 18:27:44 -0800 (PST) From: Rajasi Mandal To: sfrench@samba.org, linux-cifs@vger.kernel.org Cc: pc@manguebit.org, ronniesahlberg@gmail.com, sprasad@microsoft.com, tom@talpey.com, bharathsm@microsoft.com, samba-technical@lists.samba.org, linux-kernel@vger.kernel.org, Rajasi Mandal Subject: [PATCH] cifs: client: allow changing multichannel mount options on remount Date: Tue, 18 Nov 2025 02:26:54 +0000 Message-ID: <20251118022655.126994-1-rajasimandalos@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Rajasi Mandal 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 from_reconfigure flag to support targeted cleanup during reconfiguration. - 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=3D1 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 --- fs/smb/client/cifsproto.h | 4 ++- fs/smb/client/connect.c | 4 ++- fs/smb/client/fs_context.c | 50 +++++++++++++++++++++++++++++++++- fs/smb/client/sess.c | 32 +++++++++++++++------- fs/smb/client/smb2pdu.c | 55 ++++++++++++++++++++++++++++---------- 5 files changed, 119 insertions(+), 26 deletions(-) diff --git a/fs/smb/client/cifsproto.h b/fs/smb/client/cifsproto.h index 3528c365a452..a1fc9e1918bc 100644 --- a/fs/smb/client/cifsproto.h +++ b/fs/smb/client/cifsproto.h @@ -649,6 +649,8 @@ int cifs_alloc_hash(const char *name, struct shash_desc= **sdesc); void cifs_free_hash(struct shash_desc **sdesc); =20 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 from_reconfigure); bool is_ses_using_iface(struct cifs_ses *ses, struct cifs_server_iface *if= ace); void cifs_ses_mark_for_reconnect(struct cifs_ses *ses); =20 @@ -674,7 +676,7 @@ 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 from_reconfigu= re); void cifs_chan_update_iface(struct cifs_ses *ses, struct TCP_Server_Info *serve= r); int diff --git a/fs/smb/client/connect.c b/fs/smb/client/connect.c index 55cb4b0cbd48..cebe4a5f54f2 100644 --- a/fs/smb/client/connect.c +++ b/fs/smb/client/connect.c @@ -3927,7 +3927,9 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct s= mb3_fs_context *ctx) ctx->prepath =3D NULL; =20 out: - cifs_try_adding_channels(mnt_ctx.ses); + smb3_update_ses_channels(mnt_ctx.ses, mnt_ctx.server, + false /* from_reconnect */, + false /* from_reconfigure */); rc =3D 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 0f894d09157b..751ed6ebd458 100644 --- a/fs/smb/client/fs_context.c +++ b/fs/smb/client/fs_context.c @@ -717,6 +717,7 @@ static int smb3_fs_context_parse_param(struct fs_contex= t *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); =20 static const struct fs_context_operations smb3_fs_context_ops =3D { @@ -1013,6 +1014,22 @@ int smb3_sync_session_ctx_passwords(struct cifs_sb_i= nfo *cifs_sb, struct cifs_se return 0; } =20 +/* + * 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 u= pdate + * with the session's channel lock. This should be called whenever the max= imum + * allowed channels for a session changes (e.g., after a remount or reconf= igure). + */ +static void smb3_sync_ses_chan_max(struct cifs_ses *ses, unsigned int max_= channels) +{ + spin_lock(&ses->chan_lock); + ses->chan_max =3D max_channels; + spin_unlock(&ses->chan_lock); +} + static int smb3_reconfigure(struct fs_context *fc) { struct smb3_fs_context *ctx =3D smb3_fc2context(fc); @@ -1095,7 +1112,38 @@ static int smb3_reconfigure(struct fs_context *fc) ses->password2 =3D new_password2; } =20 - mutex_unlock(&ses->session_mutex); + /* + * If multichannel or max_channels has changed, update the session's chan= nels accordingly. + * This may add or remove channels to match the new configuration. + */ + if ((ctx->multichannel !=3D cifs_sb->ctx->multichannel) || + (ctx->max_channels !=3D 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); + return -EINVAL; + } + ses->flags |=3D CIFS_SES_FLAG_SCALE_CHANNELS; + spin_unlock(&ses->ses_lock); + + mutex_unlock(&ses->session_mutex); + + rc =3D smb3_update_ses_channels(ses, ses->server, + false /* from_reconnect */, + true /* from_reconfigure */); + + /* Clear scaling flag after operation */ + spin_lock(&ses->ses_lock); + ses->flags &=3D ~CIFS_SES_FLAG_SCALE_CHANNELS; + spin_unlock(&ses->ses_lock); + } else { + mutex_unlock(&ses->session_mutex); + } =20 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 ef3b498b0a02..cfd83986a84a 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) } =20 /* - * 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 secondar= y channels + * @ses: pointer to the CIFS session structure + * @from_reconfigure: if true, only reduce to chan_max; if false, reduce t= o a single channel + * + * This function disables and cleans up extra secondary channels for a CIF= S session. + * If called during reconfiguration, it reduces the channel count to the n= ew 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 from_reconfigu= re) { int i, chan_count; struct TCP_Server_Info *server; @@ -281,12 +285,13 @@ cifs_disable_secondary_channels(struct cifs_ses *ses) if (chan_count =3D=3D 1) goto done; =20 - ses->chan_count =3D 1; - - /* for all secondary channels reset the need reconnect bit */ - ses->chans_need_reconnect &=3D 1; + /* Update the chan_count to the new maximum */ + if (from_reconfigure) + ses->chan_count =3D ses->chan_max; + else + ses->chan_count =3D 1; =20 - for (i =3D 1; i < chan_count; i++) { + for (i =3D ses->chan_max ; i < chan_count; i++) { iface =3D ses->chans[i].iface; server =3D ses->chans[i].server; =20 @@ -318,6 +323,15 @@ cifs_disable_secondary_channels(struct cifs_ses *ses) spin_lock(&ses->chan_lock); } =20 + /* For extra secondary channels, reset the need reconnect bit */ + if (ses->chan_count =3D=3D 1) { + cifs_dbg(VFS, "server does not support multichannel anymore. Disable all= other channels\n"); + ses->chans_need_reconnect &=3D 1; + } else { + cifs_dbg(VFS, "Disable extra secondary channels\n"); + ses->chans_need_reconnect &=3D ((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 8b4a4573e9c3..d051da46eaab 100644 --- a/fs/smb/client/smb2pdu.c +++ b/fs/smb/client/smb2pdu.c @@ -168,7 +168,7 @@ smb2_hdr_assemble(struct smb2_hdr *shdr, __le16 smb2_cm= d, static int cifs_chan_skip_or_disable(struct cifs_ses *ses, struct TCP_Server_Info *server, - bool from_reconnect) + bool from_reconnect, bool from_reconfigure) { struct TCP_Server_Info *pserver; unsigned int chan_index; @@ -206,14 +206,41 @@ cifs_chan_skip_or_disable(struct cifs_ses *ses, return -EHOSTDOWN; } =20 - cifs_server_dbg(VFS, - "server does not support multichannel anymore. Disable all other channel= s\n"); - cifs_disable_secondary_channels(ses); - + cifs_decrease_secondary_channels(ses, from_reconfigure); =20 return 0; } =20 +/* + * smb3_update_ses_channels - Synchronize session channels with new config= uration + * @ses: pointer to the CIFS session structure + * @server: pointer to the TCP server info structure + * @from_reconnect: indicates if called from reconnect context + * @from_reconfigure: indicates if called from reconfigure context + * + * Returns 0 on success or error code on failure. + * + * Note: Outside of reconfigure, this function is only called from reconne= ct scenarios + * when the server stops advertising multichannel (MC) capability. + */ +int smb3_update_ses_channels(struct cifs_ses *ses, struct TCP_Server_Info = *server, + bool from_reconnect, bool from_reconfigure) +{ + int rc =3D 0; + /* + * If the current channel count is less than the new chan_max, + * try to add channels to reach the new maximum. + * Otherwise, disable or skip extra channels to match the new configurati= on. + */ + if (ses->chan_count < ses->chan_max) + rc =3D cifs_try_adding_channels(ses); + else + rc =3D cifs_chan_skip_or_disable(ses, server, from_reconnect, + from_reconfigure); + + return rc; +} + static int smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon, struct TCP_Server_Info *server, bool from_reconnect) @@ -355,8 +382,8 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *t= con, */ if (ses->chan_count > 1 && !(server->capabilities & SMB2_GLOBAL_CAP_MULTI_CHANNEL)) { - rc =3D cifs_chan_skip_or_disable(ses, server, - from_reconnect); + rc =3D smb3_update_ses_channels(ses, server, + from_reconnect, false /* from_reconfigure */); if (rc) { mutex_unlock(&ses->session_mutex); goto out; @@ -438,8 +465,9 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *t= con, * treat this as server not supporting multichannel */ =20 - rc =3D cifs_chan_skip_or_disable(ses, server, - from_reconnect); + rc =3D smb3_update_ses_channels(ses, server, + from_reconnect, + false /* from_reconfigure */); goto skip_add_channels; } else if (rc) cifs_tcon_dbg(FYI, "%s: failed to query server interfaces: %d\n", @@ -451,7 +479,8 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *t= con, if (ses->chan_count =3D=3D 1) cifs_server_dbg(VFS, "supports multichannel now\n"); =20 - cifs_try_adding_channels(ses); + smb3_update_ses_channels(ses, server, from_reconnect, + false /* from_reconfigure */); } } else { mutex_unlock(&ses->session_mutex); @@ -1105,8 +1134,7 @@ SMB2_negotiate(const unsigned int xid, req->SecurityMode =3D 0; =20 req->Capabilities =3D cpu_to_le32(server->vals->req_capabilities); - if (ses->chan_max > 1) - req->Capabilities |=3D cpu_to_le32(SMB2_GLOBAL_CAP_MULTI_CHANNEL); + req->Capabilities |=3D cpu_to_le32(SMB2_GLOBAL_CAP_MULTI_CHANNEL); =20 /* ClientGUID must be zero for SMB2.02 dialect */ if (server->vals->protocol_id =3D=3D SMB20_PROT_ID) @@ -1312,8 +1340,7 @@ int smb3_validate_negotiate(const unsigned int xid, s= truct cifs_tcon *tcon) =20 pneg_inbuf->Capabilities =3D cpu_to_le32(server->vals->req_capabilities); - if (tcon->ses->chan_max > 1) - pneg_inbuf->Capabilities |=3D cpu_to_le32(SMB2_GLOBAL_CAP_MULTI_CHANNEL); + pneg_inbuf->Capabilities |=3D cpu_to_le32(SMB2_GLOBAL_CAP_MULTI_CHANNEL); =20 memcpy(pneg_inbuf->Guid, server->client_guid, SMB2_CLIENT_GUID_SIZE); --=20 2.43.0