From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-f50.google.com (mail-ej1-f50.google.com [209.85.218.50]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CBC0B4EBAEC for ; Fri, 4 Sep 2026 15:03:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.50 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788534197; cv=none; b=aqC36SAZi1wSppnzlOYQDWiABmFmy6Xeu8iAGffgUvvnELqYKsQo70HN4M8mWsT/ln55YraUz1PZUMuHiqW6d/b2aK5BjvR3dSXsivm2wS0GUxMI44iOdr4Y969vFRqR8bClooZeBNPLnCE7OgeNTNokAuFP3w4SEFkMEqf+JQQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788534197; c=relaxed/simple; bh=6RcqfWTpR9cSAA7gQiwQ0i4hUp/8e4bbFr3Xg/BPp9k=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=p70aUH7D+0/ShoRc3LnJBB462AOGk7v9IantFGe5qhQeQqu2CZHv5EKzW/OuO9tRAvFbla86u3FcmRHH5VjNpG+McW9DxbwyI0WbkJJDVx8cxYlFC9E5crD0H2R95did67QaxuUK5ptUJpS2bxz4FfxyIt1ty4ONatyRsGfPRWY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=ionos.com; spf=pass smtp.mailfrom=ionos.com; dkim=pass (2048-bit key) header.d=ionos.com header.i=@ionos.com header.b=W0KNwZ9z; arc=none smtp.client-ip=209.85.218.50 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=ionos.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ionos.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ionos.com header.i=@ionos.com header.b="W0KNwZ9z" Received: by mail-ej1-f50.google.com with SMTP id a640c23a62f3a-c15e592da74so132479366b.1 for ; Fri, 04 Sep 2026 08:03:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ionos.com; s=google; t=1788534193; x=1789138993; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to:content-type; bh=NPdoZec4iRzjfMWUlv4D9QHImQ8qSXuSr3RPA6jeV48=; b=W0KNwZ9z8LmrZGcIAtOzKp+85vNnLoxXfmkkKfcKvn3ZSHhX4eZYcEmyhly1T1/yJF B+bxLSxaitpKR2aWAtXNy0YSG6s2ZL/BUN+pZBXrId212byn+FluHRKV7B1PtxKBMLcq +/kBMqzjy6ZETHZtMIrLvzG+0/FKRX8uxs9PZiyWLmNVBx5gwTE+kHVjcfdDJbDFppg5 +BQCJb39l+P0DsaD8Eh7ON6INsFDl+CrclB8fN/FvdxJL6+p+BtRU8sl2OrGCPb1gJvd Fj1U9owcnSRahjo2d//07lW1sUmB2d0BuJPdeS3D1JX7XP+nFIjmZ1bK3K8WfwIiduuy VNDg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1788534193; x=1789138993; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to:content-type; bh=NPdoZec4iRzjfMWUlv4D9QHImQ8qSXuSr3RPA6jeV48=; b=RSHctd2AYb9/+LI6cnEUb0jXsLXmlrgDGDQekSjGxAjH02SpH5XaymDB7AbZKKCPZt nbh32Gs9AUL+mju0kWJoucSjiZbuM+yN7SMAvsrJlAZt9/Rfn19f+DR2e6ciqatbi+k0 CTH/MQkJiZd/YKi5Sz8S+nnW/MpyEK9lCbdtFlcQSbMYuBNLorLyxjus1lYjRfq7AMp6 OQr/0kMaj2xTMp9EwmXycViFF6jKVyepLYlKcGcnwJB6VRapTQlJ9IZqB1S3CIjEeSSd BQz2ffoVu6CPP9PE182qUiftU5+nDddcePzaUKUaMQHdATA0sqF5FuvdzgFxnJ6b7Fq5 CBLQ== X-Forwarded-Encrypted: i=1; AKwUvBxBIPyygeg/jUkj/WiltMDD7Zm583NrTMtbMXWDgoL3WmzpZJG38RGRnyL/DpJwf6Yv9AbTj6IfH7G+i5g=@vger.kernel.org X-Gm-Message-State: AFuF++my5oDMWjQPxo231PCsQM6c9B9cA7JyyneIq7nrWhScaN9Tsnhg fq+r/DKgqY4ORWj0F6in1kzqhmvGu4KhVE2NRErCdIymDz5zK4ANXbIhlIUg5PtkiLs= X-Gm-Gg: AYBFou3fSpbbDfjbXDA51vSMR8gTqrJDTTWsm/fEbp6gS3N/obb8SOWUIstfeU3hQGM 9Nuh6ibYKcp7XX/FSpWlb9SnyfxmF5Qo8pyciOCjt5524H98/MS1J5io4t6cBqNca/sf89Wq986 OHCtp07UJ07zxCb6bCHEcJh5sNuE94LXgkpupbu6/SoO3iEe6dviByh9jPzzwytOXV2vUNUaHgY 6aaS9afoj2yYFdfgmRy+unKawDG05ZKu190KcrPi4EKH7WFl4Hl7O+PL2UHy4u+eeF93nmuX2+Q LQOUQT7kzCxMZz2e6XloC20Pa2FGWBDKcVcgBX56FkE7vqmu7GNX63hGfN4n0VGe9E4cbwrP3VU JWAzHUbn98C8MhasUq/BbghpIdPiYTwMGbBh4lB3XX3YT4IyUqjxrClFpZWWHvwrqiovGEkLJ3/ C/8segHX/Nvb7jN/TI4ouem1HNM7jEDGpuYaiVb5V1P//SmnpY/KujIIDvu43IFR2HCS5v5UGX1 QgPFwfgmKM/tfNJ3A4nTtlEVl8TMha1f1+vErp2jRxe+J/YQMi2cBmqYT0rOtQ/ X-Received: by 2002:a17:907:a892:b0:c20:3402:bd35 with SMTP id a640c23a62f3a-c260c988d8cmr286054566b.12.1788534192795; Fri, 04 Sep 2026 08:03:12 -0700 (PDT) Received: from raven.intern.cm-ag (p200300dc6f04b700023064fffe740809.dip0.t-ipconnect.de. [2003:dc:6f04:b700:230:64ff:fe74:809]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c260d6e1c93sm122438866b.63.2026.09.04.08.03.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Sep 2026 08:03:12 -0700 (PDT) From: Max Kellermann To: idryomov@gmail.com, amarkuze@redhat.com, xiubo.li@clyso.com, ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Max Kellermann , stable@vger.kernel.org Subject: [PATCH v4 3/3] ceph: don't unregister an MDS session before removing its caps Date: Fri, 4 Sep 2026 17:03:04 +0200 Message-ID: <20260904150304.49104-4-max.kellermann@ionos.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260904150304.49104-1-max.kellermann@ionos.com> References: <20260904150304.49104-1-max.kellermann@ionos.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit handle_session() removed the session from mdsc->sessions[] at the very top of `CEPH_SESSION_CLOSE` handling, before taking `s_mutex`. Between session unregistration and remove_session_caps(), the MDS rank has no registered session while the old session still owns all caps it was granted. Any concurrent filesystem operation may walk into that and the next __do_request() call registers a new session for this rank. Once it is open and the MDS issues caps, ceph_fill_inode() calls ceph_add_cap(), which looks caps up by rank, not by session identity, finding old caps linked to the old session. The list_move_tail() call then moves the cap object to the new session, which is already a bad thing to do. Since it doesn't decrement `old_session->s_nr_caps`, this quickly triggers: kernel BUG at fs/ceph/mds_client.c:1959! Internal error: Oops - BUG: 00000000f2000800 [#1] SMP [...] Workqueue: ceph-msgr ceph_con_workfn pstate: 20400009 (nzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : remove_session_caps+0x2bc/0x2d8 lr : remove_session_caps+0x74/0x2d8 [...] Call trace: remove_session_caps+0x2bc/0x2d8 (P) mds_dispatch+0xf48/0x1b60 ceph_con_process_message+0x74/0xa0 ceph_con_v1_try_read+0x3a0/0x1510 ceph_con_workfn+0x260/0x460 process_one_work+0x168/0x3b8 worker_thread+0x1bc/0x3a0 kthread+0x118/0x1e0 ret_from_fork+0x10/0x20 That's BUG_ON(session->s_nr_caps > 0). I was able to reproduce this reliably by delaying the close and starting I/O during the delay. This patch keeps the session registered with `CEPH_MDS_SESSION_CLOSED`. New requests will be put on the `s_waiting` list where they will be resumed on the new session. Since `CLOSE` now sets `CLOSED` before taking `s_mutex`, make send_mds_reconnect() validate and update the session state under `mdsc->mutex`. Preserve `CLOSED` if reconnect preparation later fails. Fixes: 2600d2dd5085 ("ceph: drop messages on unregistered mds sessions; cleanup") Cc: stable@vger.kernel.org Signed-off-by: Max Kellermann --- fs/ceph/caps.c | 4 + fs/ceph/mds_client.c | 182 ++++++++++++++++++++++++++++++++++++------- 2 files changed, 156 insertions(+), 30 deletions(-) diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c index bcb04c6cb92c..024714d7f34e 100644 --- a/fs/ceph/caps.c +++ b/fs/ceph/caps.c @@ -4261,6 +4261,10 @@ static void handle_cap_export(struct inode *inode, struct ceph_mds_caps *ex, } new_cap = ceph_get_cap(mdsc, NULL); } else { + if (tsession == ERR_PTR(-EAGAIN)) + /* locks already dropped */ + return; + WARN_ON(1); tsession = NULL; target = -1; diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c index 86d592f06196..f091f0eaafc2 100644 --- a/fs/ceph/mds_client.c +++ b/fs/ceph/mds_client.c @@ -1783,6 +1783,30 @@ static int __open_session(struct ceph_mds_client *mdsc, return 0; } +/* Is this rank still occupied by a session being torn down? */ +static bool __mds_rank_closing(struct ceph_mds_client *mdsc, int mds) +{ + return mds < mdsc->max_sessions && mdsc->sessions[mds] && + mdsc->sessions[mds]->s_state == CEPH_MDS_SESSION_CLOSED; +} + +/* + * Wait until the rank is no longer occupied by a CLOSED session. + * + * The caller must hold mdsc->mutex. The mutex is dropped while sleeping and + * held again on return. Another session may occupy the rank by then. The + * wait also ends when shutdown starts, so the caller must check + * mdsc->stopping before proceeding. + */ +static void wait_for_mds_rank_not_closing(struct ceph_mds_client *mdsc, + int mds) +{ + wait_event_cmd(mdsc->session_close_wq, + !__mds_rank_closing(mdsc, mds) || mdsc->stopping, + mutex_unlock(&mdsc->mutex), + mutex_lock(&mdsc->mutex)); +} + /* * open sessions for any export targets for the given mds * @@ -1800,6 +1824,16 @@ __open_export_target_session(struct ceph_mds_client *mdsc, int target) if (IS_ERR(session)) return session; } + if (session->s_state == CEPH_MDS_SESSION_CLOSED) { + /* + * handle_session() is currently closing this session; + * it stays registered until its caps are gone. Do + * not return it to our caller because we don't want + * it to attach new caps to it. + */ + ceph_put_mds_session(session); + return ERR_PTR(-EAGAIN); + } if (session->s_state == CEPH_MDS_SESSION_NEW || session->s_state == CEPH_MDS_SESSION_CLOSING) { ret = __open_session(mdsc, session); @@ -1819,7 +1853,19 @@ ceph_mdsc_open_export_target_session(struct ceph_mds_client *mdsc, int target) doutc(cl, "to mds%d\n", target); mutex_lock(&mdsc->mutex); - session = __open_export_target_session(mdsc, target); + for (;;) { + session = __open_export_target_session(mdsc, target); + if (session != ERR_PTR(-EAGAIN) || mdsc->stopping) + break; + + /* + * Keep the exported cap on its old session until the + * target rank is vacant. Dropping it here can discard a + * dirty auth cap; handle_session() wakes us after removing + * the old target session's caps and unregistering it. + */ + wait_for_mds_rank_not_closing(mdsc, target); + } mutex_unlock(&mdsc->mutex); return session; @@ -4553,8 +4599,20 @@ static void handle_session(struct ceph_mds_session *session, ceph_metric_bind_session(mdsc, session); } if (op == CEPH_SESSION_CLOSE) { + /* + * Pin the session for the rest of this function. The + * __unregister_session() call is deferred until after + * remove_session_caps() below, or else other + * processes may find caps still assigned to this + * session while working with a new session object. + */ ceph_get_mds_session(session); - __unregister_session(mdsc, session); + + if (session->s_state == CEPH_MDS_SESSION_RECONNECTING) + pr_info_client(cl, "mds%d reconnect denied\n", + session->s_mds); + + session->s_state = CEPH_MDS_SESSION_CLOSED; } /* FIXME: this ttl calculation is generous */ session->s_ttl = jiffies + HZ*mdsc->mdsmap->m_session_autoclose; @@ -4612,12 +4670,24 @@ static void handle_session(struct ceph_mds_session *session, break; case CEPH_SESSION_CLOSE: - if (session->s_state == CEPH_MDS_SESSION_RECONNECTING) - pr_info_client(cl, "mds%d reconnect denied\n", - session->s_mds); - session->s_state = CEPH_MDS_SESSION_CLOSED; cleanup_session_requests(mdsc, session); remove_session_caps(session); + + /* + * Now that all caps are removed, it is safe to release + * the MDS rank and allow other processes to create a + * new session object. + * + * A concurrent ceph_mdsc_close_sessions() or + * check_new_map() may have unregistered the session + * already, so check __verify_registered_session() + * first. + */ + mutex_lock(&mdsc->mutex); + if (!__verify_registered_session(mdsc, session)) + __unregister_session(mdsc, session); + mutex_unlock(&mdsc->mutex); + wake = 2; /* for good measure */ wake_up_all(&mdsc->session_close_wq); break; @@ -5168,16 +5238,6 @@ static int send_mds_reconnect(struct ceph_mds_client *mdsc, /* Serialized by s_mutex against concurrent ceph_get_deleg_ino(). */ xa_destroy(&session->s_delegated_inos); atomic_set(&session->s_num_deleg_inos, 0); - if (session->s_state == CEPH_MDS_SESSION_CLOSED || - session->s_state == CEPH_MDS_SESSION_REJECTED) { - pr_info_client(cl, "mds%d skipping reconnect, session %s\n", - mds, - ceph_session_state_name(session->s_state)); - mutex_unlock(&session->s_mutex); - ceph_msg_put(reply); - err = -ESTALE; - goto fail_return; - } /* s_mutex -> mdsc->mutex matches cleanup_session_requests() order. */ mutex_lock(&mdsc->mutex); @@ -5191,12 +5251,23 @@ static int send_mds_reconnect(struct ceph_mds_client *mdsc, err = -ENOENT; goto fail_return; } - mutex_unlock(&mdsc->mutex); + if (session->s_state == CEPH_MDS_SESSION_CLOSED || + session->s_state == CEPH_MDS_SESSION_REJECTED) { + mutex_unlock(&mdsc->mutex); + pr_info_client(cl, "mds%d skipping reconnect, session %s\n", + mds, + ceph_session_state_name(session->s_state)); + mutex_unlock(&session->s_mutex); + ceph_msg_put(reply); + err = -ESTALE; + goto fail_return; + } pr_info_client(cl, "mds%d reconnect start\n", mds); old_state = session->s_state; session->s_state = CEPH_MDS_SESSION_RECONNECTING; session->s_seq = 0; + mutex_unlock(&mdsc->mutex); doutc(cl, "session %p state %s\n", session, ceph_session_state_name(session->s_state)); @@ -5338,7 +5409,10 @@ static int send_mds_reconnect(struct ceph_mds_client *mdsc, * (check_new_map) can retry. Without this, a transient build * failure strands the session in RECONNECTING indefinitely. */ - session->s_state = old_state; + mutex_lock(&mdsc->mutex); + if (session->s_state == CEPH_MDS_SESSION_RECONNECTING) + session->s_state = old_state; + mutex_unlock(&mdsc->mutex); mutex_unlock(&session->s_mutex); fail_nomsg: ceph_pagelist_release(recon_state.pagelist); @@ -5746,23 +5820,29 @@ static void ceph_mdsc_reset_workfn(struct work_struct *work) continue; } sessions[i]->s_state = CEPH_MDS_SESSION_CLOSED; - __unregister_session(mdsc, sessions[i]); - __wake_requests(mdsc, &sessions[i]->s_waiting); mutex_unlock(&mdsc->mutex); mutex_lock(&sessions[i]->s_mutex); cleanup_session_requests(mdsc, sessions[i]); remove_session_caps(sessions[i]); + + /* Keep the rank occupied until all old-session caps are gone. */ + mutex_lock(&mdsc->mutex); + if (!__verify_registered_session(mdsc, sessions[i])) + __unregister_session(mdsc, sessions[i]); + mutex_unlock(&mdsc->mutex); + mutex_unlock(&sessions[i]->s_mutex); wake_up_all(&mdsc->session_close_wq); - ceph_put_mds_session(sessions[i]); - mutex_lock(&mdsc->mutex); + __wake_requests(mdsc, &sessions[i]->s_waiting); kick_requests(mdsc, mds); mutex_unlock(&mdsc->mutex); + ceph_put_mds_session(sessions[i]); + torn_down++; pr_info_client(cl, "mds%d session reset complete\n", mds); } @@ -5864,6 +5944,12 @@ static void check_new_map(struct ceph_mds_client *mdsc, s = __ceph_lookup_mds_session(mdsc, i); if (!s) continue; + + if (s->s_state == CEPH_MDS_SESSION_CLOSED) { + ceph_put_mds_session(s); + continue; + } + oldstate = ceph_mdsmap_get_state(oldmap, i); newstate = ceph_mdsmap_get_state(newmap, i); @@ -5876,18 +5962,24 @@ static void check_new_map(struct ceph_mds_client *mdsc, if (i >= newmap->possible_max_rank) { /* force close session for stopped mds */ - __unregister_session(mdsc, s); - __wake_requests(mdsc, &s->s_waiting); + s->s_state = CEPH_MDS_SESSION_CLOSED; mutex_unlock(&mdsc->mutex); mutex_lock(&s->s_mutex); cleanup_session_requests(mdsc, s); remove_session_caps(s); + + mutex_lock(&mdsc->mutex); + if (!__verify_registered_session(mdsc, s)) + __unregister_session(mdsc, s); + mutex_unlock(&mdsc->mutex); mutex_unlock(&s->s_mutex); - ceph_put_mds_session(s); + wake_up_all(&mdsc->session_close_wq); mutex_lock(&mdsc->mutex); + __wake_requests(mdsc, &s->s_waiting); + ceph_put_mds_session(s); if (mdsc->mdsmap->m_epoch != map_epoch) return; kick_requests(mdsc, i); @@ -5906,6 +5998,16 @@ static void check_new_map(struct ceph_mds_client *mdsc, ceph_put_mds_session(s); return; } + if (s->s_state == CEPH_MDS_SESSION_CLOSED) { + /* + * handle_session() set state=CLOSED + * in the mutex gap above and is tearing it + * down + */ + mutex_unlock(&s->s_mutex); + ceph_put_mds_session(s); + continue; + } ceph_con_close(&s->s_con); mutex_unlock(&s->s_mutex); s->s_state = CEPH_MDS_SESSION_RESTARTING; @@ -5964,6 +6066,9 @@ static void check_new_map(struct ceph_mds_client *mdsc, * Only open and reconnect sessions that don't exist yet. */ for (i = 0; i < newmap->possible_max_rank; i++) { + if (mdsc->stopping) + return; + /* * In case the import MDS is crashed just after * the EImportStart journal is flushed, so when @@ -5989,6 +6094,19 @@ static void check_new_map(struct ceph_mds_client *mdsc, * reconnection request in up:reconnect state. */ s = __ceph_lookup_mds_session(mdsc, i); + if (s && s->s_state == CEPH_MDS_SESSION_CLOSED) { + /* + * Wait for handle_session() to remove the caps and + * unregister this session, so the reconnect below + * uses a fresh session on the now vacant rank + */ + ceph_put_mds_session(s); + wait_for_mds_rank_not_closing(mdsc, i); + if (mdsc->stopping || + mdsc->mdsmap->m_epoch != map_epoch) + return; + s = NULL; + } if (likely(!s)) { s = __open_export_target_session(mdsc, i); if (IS_ERR(s)) { @@ -7149,9 +7267,7 @@ static void mds_peer_reset(struct ceph_connection *con) * Snapshot session state with READ_ONCE, then revalidate under * mdsc->mutex before acting. The subsequent mdsc->mutex * section rechecks s_state to catch concurrent transitions, so - * the lockless snapshot here is safe. s->s_mutex is taken - * separately for cleanup after unregistration, which avoids - * introducing a new s->s_mutex + mdsc->mutex nesting. + * the lockless snapshot here is safe. */ session_state = READ_ONCE(s->s_state); @@ -7176,18 +7292,24 @@ static void mds_peer_reset(struct ceph_connection *con) ceph_get_mds_session(s); s->s_state = CEPH_MDS_SESSION_CLOSED; - __unregister_session(mdsc, s); - __wake_requests(mdsc, &s->s_waiting); mutex_unlock(&mdsc->mutex); mutex_lock(&s->s_mutex); cleanup_session_requests(mdsc, s); remove_session_caps(s); + + /* Keep the rank occupied until all old-session caps are gone. */ + mutex_lock(&mdsc->mutex); + if (!__verify_registered_session(mdsc, s)) + __unregister_session(mdsc, s); + mutex_unlock(&mdsc->mutex); + mutex_unlock(&s->s_mutex); wake_up_all(&mdsc->session_close_wq); mutex_lock(&mdsc->mutex); + __wake_requests(mdsc, &s->s_waiting); kick_requests(mdsc, s->s_mds); mutex_unlock(&mdsc->mutex); -- 2.47.3