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Message-ID: <CAEY6_V2Rc_yBSTL3ozK1TJo-qM0HixeE5kgXiPuOS5g2MZAErg@mail.gmail.com>
Date: Mon, 1 Dec 2025 14:51:13 +0530
From: RAJASI MANDAL <rajasimandalos@...il.com>
To: Shyam Prasad N <nspmangalore@...il.com>
Cc: Meetakshi Setiya <meetakshisetiyaoss@...il.com>, sfrench@...ba.org,
linux-cifs@...r.kernel.org, pc@...guebit.org, ronniesahlberg@...il.com,
sprasad@...rosoft.com, tom@...pey.com, bharathsm@...rosoft.com,
samba-technical@...ts.samba.org, linux-kernel@...r.kernel.org,
Rajasi Mandal <rajasimandal@...rosoft.com>
Subject: Re: [PATCH] cifs: client: allow changing multichannel mount options
on remount
Sending a follow-up patch with corrected comment as pointed out by
Meetakshi. Attaching the new patch here for easy reference.
Regards,
Rajasi
On Mon, Nov 24, 2025 at 5:20 PM Shyam Prasad N <nspmangalore@...il.com>
wrote:
> On Thu, Nov 20, 2025 at 11:40 AM Meetakshi Setiya
> <meetakshisetiyaoss@...il.com> wrote:
> >
> > Hi Rajasi,
> >
> > On Tue, Nov 18, 2025 at 7:59 AM Rajasi Mandal <rajasimandalos@...il.com>
> wrote:
> > >
> > > From: Rajasi Mandal <rajasimandal@...rosoft.com>
> > >
> > > 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=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 <sprasad@...rosoft.com>
> > > Signed-off-by: Rajasi Mandal <rajasimandal@...rosoft.com>
> > > ---
> > > 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);
> > >
> > > 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 *iface);
> > > void cifs_ses_mark_for_reconnect(struct cifs_ses *ses);
> > >
> > > @@ -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_reconfigure);
> > > 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 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 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 /* from_reconfigure */);
> >
> > Shouldn't this be added to the non-dfs cifs_mount() too? I see that
> > even cifs_try_adding_channels() is not present in this function,
> > @Shyam Prasad is this expected?
>
> That's a good catch.
> I think this is a day-0 bug.
> I can see that the original change by Aurelien has the change only in
> DFS cifs_mount:
> commit d70e9fa55884760b6d6c293dbf20d8c52ce11fb7
> Author: Aurelien Aptel <aaptel@...e.com>
> Date: Fri Sep 20 06:31:10 2019 +0200
>
> cifs: try opening channels after mounting
>
> We should have a follow-up patch to fix this.
>
> >
> > > 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 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_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 = {
> > > @@ -1013,6 +1014,22 @@ 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);
> > > @@ -1095,7 +1112,38 @@ 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);
> > > + 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
> */,
> > > + true /*
> from_reconfigure */);
> > > +
> > > + /* 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 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)
> > > }
> > >
> > > /*
> > > - * 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
> > > + * @from_reconfigure: if true, only reduce to chan_max; if false,
> reduce to a single channel
> > > + *
> > > + * 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
> from_reconfigure)
> > > {
> > > int i, chan_count;
> > > struct TCP_Server_Info *server;
> > > @@ -281,12 +285,13 @@ 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 (from_reconfigure)
> > > + ses->chan_count = ses->chan_max;
> > > + else
> > > + ses->chan_count = 1;
> > >
> > > - for (i = 1; i < chan_count; i++) {
> > > + for (i = ses->chan_max ; i < chan_count; i++) {
> > > iface = ses->chans[i].iface;
> > > server = ses->chans[i].server;
> > >
> > > @@ -318,6 +323,15 @@ 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, "server does not support multichannel
> anymore. Disable all other 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 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_cmd,
> > > 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;
> > > }
> > >
> > > - 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, from_reconfigure);
> > >
> > > 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
> > > + * @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
> reconnect scenarios
> > > + * when the server stops advertising multichannel (MC) capability.
> > > + */
> >
> > I see that function is being called during mount too. Did you
> > mean cifs_decrease_secondary_channels()?
> >
> > > +int smb3_update_ses_channels(struct cifs_ses *ses, struct
> TCP_Server_Info *server,
> > > + bool from_reconnect, bool from_reconfigure)
> > > +{
> > > + int rc = 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
> configuration.
> > > + */
> > > + if (ses->chan_count < ses->chan_max)
> > > + rc = cifs_try_adding_channels(ses);
> > > + else
> > > + rc = 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 *tcon,
> > > */
> > > 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, false
> /* from_reconfigure */);
> > > if (rc) {
> > > mutex_unlock(&ses->session_mutex);
> > > goto out;
> > > @@ -438,8 +465,9 @@ smb2_reconnect(__le16 smb2_command, struct
> cifs_tcon *tcon,
> > > * 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,
> > > + 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 *tcon,
> > > 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 /*
> from_reconfigure */);
> > > }
> > > } else {
> > > mutex_unlock(&ses->session_mutex);
> > > @@ -1105,8 +1134,7 @@ 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)
> > > @@ -1312,8 +1340,7 @@ 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);
> > > --
> > > 2.43.0
> > >
> > >
> >
> > Thanks
> > Meetakshi
> >
>
>
> --
> Regards,
> Shyam
>
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