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Fri, 21 Aug 2026 09:29:42 -0700 (PDT) Received: from bcodding.csb.hammerspace.com ([66.97.168.37]) by smtp.gmail.com with ESMTPSA id 5614622812f47-4b2d6d74145sm5002916b6e.15.2026.08.21.09.29.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 Aug 2026 09:29:41 -0700 (PDT) From: Benjamin Coddington X-Google-Original-From: Benjamin Coddington To: Trond Myklebust , Anna Schumaker Cc: linux-nfs@vger.kernel.org, Jonathan Curley , Mike Snitzer , Jeff Layton Subject: [PATCH v2 10/23] NFSv4/flexfiles: Make the pinned device node pointer RCU-managed Date: Fri, 21 Aug 2026 12:29:14 -0400 Message-ID: <4e4f73676be9ae7669719ff5ed16bf20ddbb8ee5.1787327939.git.bcodding@hammerspace.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Annotate mirror->dss[dss_id].mirror_ds as __rcu and convert the remaining readers, completing the preparation for re-pointing the pinned node while I/O is in flight: - ff_layout_get_mirror_ds() takes its reference under rcu_read_lock() with atomic_inc_not_zero(), retrying if it races a reset. The resolve path takes the caller's reference before publishing the node with cmpxchg(), so a concurrent reset cannot drop the last reference under the caller: one reference is held for the installed pointer and one for the caller, and the pointer's reference is released elsewhere by xchg + put. - The availability scans hold rcu_read_lock() across the walk; they only test flags on the RCU-freed node. - ff_layout_cancel_io() holds a reference across the cancel and disconnect calls. Both of its callers hold i_lock and nothing on that path sleeps, so the reference is not about blocking: it is what keeps the node alive between the RCU-protected read and the use of mirror_ds->ds. The final put is never reached here, because the mirror's own pin outlives the loop -- which matters, since that put ends in nfs_put_client() and cannot run under a spinlock. - ff_layout_mirror_prepare_stats() reads the pointer with rcu_dereference() under rcu_read_lock(). i_lock, which both callers hold, is what excludes the re-pointing walk added later in this series; it does not exclude the resolve path's cmpxchg(), which runs from I/O submission, so the read cannot claim i_lock as its update- side lock. A non-NULL pointer read there is stable regardless: the resolve path only ever installs over NULL. - ff_layout_free_mirror() tears down the last reference; no concurrency. The pointer is still only ever set once per mirror lifetime, so there is no behavior change; this commit makes the subsequent in-place re-resolve on CB_NOTIFY_DEVICEID CHANGE safe to introduce. Assisted-by: Claude:claude-fable-5 Signed-off-by: Benjamin Coddington --- fs/nfs/flexfilelayout/flexfilelayout.c | 35 ++++--- fs/nfs/flexfilelayout/flexfilelayout.h | 2 +- fs/nfs/flexfilelayout/flexfilelayoutdev.c | 110 ++++++++++++++-------- 3 files changed, 93 insertions(+), 54 deletions(-) diff --git a/fs/nfs/flexfilelayout/flexfilelayout.c b/fs/nfs/flexfilelayout/flexfilelayout.c index 947bb277c4ef..3572324630df 100644 --- a/fs/nfs/flexfilelayout/flexfilelayout.c +++ b/fs/nfs/flexfilelayout/flexfilelayout.c @@ -313,7 +313,9 @@ static void ff_layout_free_mirror(struct nfs4_ff_layout_mirror *mirror) cred = rcu_access_pointer(mirror->dss[dss_id].rw_cred); put_cred(cred); nfs_close_local_fh(&mirror->dss[dss_id].nfl); - nfs4_ff_layout_put_deviceid(mirror->dss[dss_id].mirror_ds); + /* the last reference to the mirror is gone; no concurrency */ + nfs4_ff_layout_put_deviceid(rcu_dereference_protected( + mirror->dss[dss_id].mirror_ds, 1)); } kfree(mirror->dss); @@ -2479,22 +2481,29 @@ static void ff_layout_cancel_io(struct pnfs_layout_segment *lseg) for (idx = 0; idx < flseg->mirror_array_cnt; idx++) { mirror = flseg->mirror_array[idx]; for (dss_id = 0; dss_id < mirror->dss_count; dss_id++) { - mirror_ds = mirror->dss[dss_id].mirror_ds; - if (IS_ERR_OR_NULL(mirror_ds)) + rcu_read_lock(); + mirror_ds = rcu_dereference(mirror->dss[dss_id].mirror_ds); + if (IS_ERR_OR_NULL(mirror_ds) || + !atomic_inc_not_zero(&mirror_ds->id_node.ref)) { + rcu_read_unlock(); continue; - ds = mirror->dss[dss_id].mirror_ds->ds; + } + rcu_read_unlock(); + ds = mirror_ds->ds; if (!ds) - continue; + goto next; ds_clp = ds->ds_clp; if (!ds_clp) - continue; + goto next; clnt = ds_clp->cl_rpcclient; if (!clnt) - continue; + goto next; if (!rpc_cancel_tasks(clnt, -EAGAIN, ff_layout_match_io, lseg)) - continue; + goto next; rpc_clnt_disconnect(clnt); +next: + nfs4_ff_layout_put_deviceid(mirror_ds); } } } @@ -2956,12 +2965,13 @@ ff_layout_mirror_prepare_stats(struct pnfs_layout_hdr *lo, struct nfs4_ff_layout_ds *mirror_ds; int i = 0, dss_id; + rcu_read_lock(); list_for_each_entry(mirror, &ff_layout->mirrors, mirrors) { for (dss_id = 0; dss_id < mirror->dss_count; ++dss_id) { dss_info = &mirror->dss[dss_id]; if (i >= dev_limit) break; - mirror_ds = dss_info->mirror_ds; + mirror_ds = rcu_dereference(dss_info->mirror_ds); if (IS_ERR_OR_NULL(mirror_ds)) continue; if (!test_and_clear_bit(NFS4_FF_MIRROR_STAT_AVAIL, @@ -2971,10 +2981,8 @@ ff_layout_mirror_prepare_stats(struct pnfs_layout_hdr *lo, /* mirror refcount put in cleanup_layoutstats */ if (!refcount_inc_not_zero(&mirror->ref)) continue; - /* - * The mirror's pin holds the node while we're under - * i_lock; take a reference for the encode, put in - * ff_layout_free_layoutstats(). + /* The pin holds a reference; it is exchanged out only + * under i_lock. Put in ff_layout_free_layoutstats(). */ atomic_inc(&mirror_ds->id_node.ref); memcpy(&devinfo->dev_id, @@ -3003,6 +3011,7 @@ ff_layout_mirror_prepare_stats(struct pnfs_layout_hdr *lo, i++; } } + rcu_read_unlock(); return i; } diff --git a/fs/nfs/flexfilelayout/flexfilelayout.h b/fs/nfs/flexfilelayout/flexfilelayout.h index d6ec80cf8a6e..54e87847ee45 100644 --- a/fs/nfs/flexfilelayout/flexfilelayout.h +++ b/fs/nfs/flexfilelayout/flexfilelayout.h @@ -79,7 +79,7 @@ struct nfs4_ff_layout_ds_stripe { struct nfs4_ff_layout_mirror *mirror; struct nfs4_deviceid devid; u32 efficiency; - struct nfs4_ff_layout_ds *mirror_ds; + struct nfs4_ff_layout_ds __rcu *mirror_ds; u32 fh_versions_cnt; struct nfs_fh *fh_versions; nfs4_stateid stateid; diff --git a/fs/nfs/flexfilelayout/flexfilelayoutdev.c b/fs/nfs/flexfilelayout/flexfilelayoutdev.c index 54349d9a89db..f0254ee6a9a8 100644 --- a/fs/nfs/flexfilelayout/flexfilelayoutdev.c +++ b/fs/nfs/flexfilelayout/flexfilelayoutdev.c @@ -333,35 +333,54 @@ ff_layout_get_mirror_ds(struct pnfs_layout_hdr *lo, struct nfs4_ff_layout_mirror *mirror, u32 dss_id) { - struct nfs4_ff_layout_ds *mirror_ds; + struct nfs4_ff_layout_ds *mirror_ds, *old; + struct nfs4_deviceid_node *node; if (mirror == NULL) return ERR_PTR(-ENODEV); - mirror_ds = mirror->dss[dss_id].mirror_ds; - if (mirror_ds == NULL) { - struct nfs4_deviceid_node *node; - +retry: + rcu_read_lock(); + mirror_ds = rcu_dereference(mirror->dss[dss_id].mirror_ds); + if (mirror_ds && !IS_ERR(mirror_ds) && + atomic_inc_not_zero(&mirror_ds->id_node.ref)) { + rcu_read_unlock(); + return mirror_ds; + } + rcu_read_unlock(); + if (IS_ERR(mirror_ds)) + return mirror_ds; + if (mirror_ds != NULL) + /* raced with a reset; the field is being re-pointed */ + goto retry; + + node = nfs4_find_get_deviceid(NFS_SERVER(lo->plh_inode), + &mirror->dss[dss_id].devid, lo->plh_lc_cred, + GFP_KERNEL); + if (node) { + mirror_ds = FF_LAYOUT_MIRROR_DS(node); + /* + * Take the caller's reference before the pointer becomes + * visible below, so a concurrent reset of the installed + * pointer cannot drop the last reference under us. + */ + atomic_inc(&node->ref); + } else { mirror_ds = ERR_PTR(-ENODEV); - node = nfs4_find_get_deviceid(NFS_SERVER(lo->plh_inode), - &mirror->dss[dss_id].devid, lo->plh_lc_cred, - GFP_KERNEL); - if (node) - mirror_ds = FF_LAYOUT_MIRROR_DS(node); - - /* check for race with another call to this function */ - if (cmpxchg(&mirror->dss[dss_id].mirror_ds, NULL, mirror_ds) && - mirror_ds != ERR_PTR(-ENODEV)) - nfs4_put_deviceid_node(node); - - mirror_ds = mirror->dss[dss_id].mirror_ds; } - if (IS_ERR(mirror_ds)) + /* check for race with another call to this function */ + old = unrcu_pointer(cmpxchg(&mirror->dss[dss_id].mirror_ds, + NULL, RCU_INITIALIZER(mirror_ds))); + if (old == NULL) return mirror_ds; - if (!atomic_inc_not_zero(&mirror_ds->id_node.ref)) - return ERR_PTR(-ENODEV); - return mirror_ds; + + /* lost the race; use the winner's node instead */ + if (node) { + nfs4_put_deviceid_node(node); + nfs4_put_deviceid_node(node); + } + goto retry; } /** @@ -584,49 +603,60 @@ unsigned int ff_layout_fetch_ds_ioerr(struct pnfs_layout_hdr *lo, static bool ff_read_layout_has_available_ds(struct pnfs_layout_segment *lseg) { struct nfs4_ff_layout_mirror *mirror; - struct nfs4_deviceid_node *devid; + struct nfs4_ff_layout_ds *mirror_ds; + bool ret = false; u32 idx, dss_id; + rcu_read_lock(); for (idx = 0; idx < FF_LAYOUT_MIRROR_COUNT(lseg); idx++) { mirror = FF_LAYOUT_COMP(lseg, idx); if (!mirror) continue; for (dss_id = 0; dss_id < mirror->dss_count; dss_id++) { - if (!mirror->dss[dss_id].mirror_ds) - return true; - if (IS_ERR(mirror->dss[dss_id].mirror_ds)) + mirror_ds = rcu_dereference(mirror->dss[dss_id].mirror_ds); + if (!mirror_ds) { + ret = true; + goto out; + } + if (IS_ERR(mirror_ds)) continue; - devid = &mirror->dss[dss_id].mirror_ds->id_node; - if (!nfs4_test_deviceid_unavailable(devid)) - return true; + if (!nfs4_test_deviceid_unavailable(&mirror_ds->id_node)) { + ret = true; + goto out; + } } } - - return false; +out: + rcu_read_unlock(); + return ret; } static bool ff_rw_layout_has_available_ds(struct pnfs_layout_segment *lseg) { struct nfs4_ff_layout_mirror *mirror; - struct nfs4_deviceid_node *devid; + struct nfs4_ff_layout_ds *mirror_ds; + bool ret = false; u32 idx, dss_id; + rcu_read_lock(); for (idx = 0; idx < FF_LAYOUT_MIRROR_COUNT(lseg); idx++) { mirror = FF_LAYOUT_COMP(lseg, idx); if (!mirror) - return false; + goto out; for (dss_id = 0; dss_id < mirror->dss_count; dss_id++) { - if (IS_ERR(mirror->dss[dss_id].mirror_ds)) - return false; - if (!mirror->dss[dss_id].mirror_ds) + mirror_ds = rcu_dereference(mirror->dss[dss_id].mirror_ds); + if (IS_ERR(mirror_ds)) + goto out; + if (!mirror_ds) continue; - devid = &mirror->dss[dss_id].mirror_ds->id_node; - if (nfs4_test_deviceid_unavailable(devid)) - return false; + if (nfs4_test_deviceid_unavailable(&mirror_ds->id_node)) + goto out; } } - - return FF_LAYOUT_MIRROR_COUNT(lseg) != 0; + ret = FF_LAYOUT_MIRROR_COUNT(lseg) != 0; +out: + rcu_read_unlock(); + return ret; } static bool ff_layout_has_available_ds(struct pnfs_layout_segment *lseg) -- 2.53.0