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[45.78.65.84]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3537cb6a279sm41437975eec.30.2026.10.13.02.18.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Oct 2026 02:18:11 -0700 (PDT) From: Chengfeng Ye To: alibuda@linux.alibaba.com, dust.li@linux.alibaba.com, sidraya@linux.ibm.com, mjambigi@linux.ibm.com, davem@davemloft.net, edumazet@kernel.org, kuba@kernel.org, pabeni@redhat.com Cc: tonylu@linux.alibaba.com, guwen@linux.alibaba.com, horms@kernel.org, linux-rdma@vger.kernel.org, linux-s390@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH net v3 1/3] net/smc: serialize link group free work scheduling Date: Tue, 13 Oct 2026 17:17:14 +0800 Message-ID: <20261013091716.1210420-2-nicoyip.dev@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261013091716.1210420-1-nicoyip.dev@gmail.com> References: <20261013091716.1210420-1-nicoyip.dev@gmail.com> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit smc_lgr_schedule_free_work() checks lgr->freeing without the link group list lock held by the teardown paths. A concurrent smc_lgr_free_work() can set freeing and cancel the delayed work between that check and mod_delayed_work(), leaving a timer pending on a freed link group: CPU 0 (smc_conn_free) CPU 1 (smc_lgr_free_work) observe lgr->freeing == 0 set lgr->freeing under lgr_lock cancel_delayed_work() smc_lgr_free(): drop lgr reference mod_delayed_work() smc_lgr_put(): drop last reference and free lgr When the timer expires, the timer core accesses the freed memory. BUG: KASAN: use-after-free in __run_timers+0x86d/0x8d0 Write of size 8 at addr ffff8881186902a8 by task swapper/2/0 Call Trace: __run_timers+0x86d/0x8d0 timer_expire_remote+0xd3/0x120 tmigr_handle_remote_up+0x4f4/0xab0 __walk_groups_from+0x40/0x150 tmigr_handle_remote+0x229/0x2c0 run_timer_softirq+0x1f5/0x250 handle_softirqs+0x18d/0x5b0 Hold the existing link group list lock across the freeing check and mod_delayed_work(). Set freeing under that lock in early cleanup as well, before __smc_lgr_terminate() cancels the work. An SMC-D server releases smc_server_lgr_pending before receiving CONFIRM, so another connection can reuse the group and race its removal with early cleanup. Give freeing its own storage. The neighbouring sync_err and terminating bitfields are written without the list lock; their read-modify-write updates must not overwrite the freeing transition. Rearming then either precedes the freeing transition and is caught by the subsequent cancellation, or sees freeing set and is skipped. smc_conn_free() retains its link group reference until after scheduling, keeping the group alive while acquiring the lock. Fixes: 8e316b9e7260 ("net/smc: improve link group freeing") Cc: stable@vger.kernel.org Assisted-by: GPT-6.1-Sol Signed-off-by: Chengfeng Ye --- Changes in v3: - Rebase onto current net/main. - Correct the cancellation comment without implying that checking freeing protects an already-running callback. Patch 3 supplies that protection. Changes in v2: - Give freeing its own storage so adjacent bitfield updates cannot overwrite the list-lock-protected transition. - Set freeing under the list lock during early cleanup to prevent a concurrent SMC-D connection from rearming after cancellation. - Keep asynchronous cancellation without adding work-owned references. - Send with the early-cleanup ownership fix as an ordered two-patch series. v1: https://lore.kernel.org/r/20260927074520.3694663-1-nicoyip.dev@gmail.com/ v2: https://lore.kernel.org/r/20261003183237.2284245-2-nicoyip.dev@gmail.com/ net/smc/smc_core.c | 8 +++++++- net/smc/smc_core.h | 2 +- 2 files changed, 8 insertions(+), 2 deletions(-) diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c index 9974149659c2..660cd41ec720 100644 --- a/net/smc/smc_core.c +++ b/net/smc/smc_core.c @@ -80,6 +80,10 @@ static void smc_ibdev_cnt_dec(struct smc_link *lnk) static void smc_lgr_schedule_free_work(struct smc_link_group *lgr) { + spinlock_t *lgr_lock; /* protects lgr->freeing */ + + smc_lgr_list_head(lgr, &lgr_lock); + spin_lock_bh(lgr_lock); /* client link group creation always follows the server link group * creation. For client use a somewhat higher removal delay time, * otherwise there is a risk of out-of-sync link groups. @@ -90,6 +94,7 @@ static void smc_lgr_schedule_free_work(struct smc_link_group *lgr) SMC_LGR_FREE_DELAY_CLNT : SMC_LGR_FREE_DELAY_SERV); } + spin_unlock_bh(lgr_lock); } /* Register connection's alert token in our lookup structure. @@ -691,6 +696,7 @@ void smc_lgr_cleanup_early(struct smc_link_group *lgr) /* do not use this link group for new connections */ if (!list_empty(&lgr->list)) list_del_init(&lgr->list); + lgr->freeing = 1; spin_unlock_bh(lgr_lock); __smc_lgr_terminate(lgr, true); } @@ -1565,7 +1571,7 @@ static void __smc_lgr_terminate(struct smc_link_group *lgr, bool soft) if (lgr->terminating) return; /* lgr already terminating */ - /* cancel free_work sync, will terminate when lgr->freeing is set */ + /* cancel pending free_work */ cancel_delayed_work(&lgr->free_work); lgr->terminating = 1; diff --git a/net/smc/smc_core.h b/net/smc/smc_core.h index 5c18f08a4c8a..b8c67f277337 100644 --- a/net/smc/smc_core.h +++ b/net/smc/smc_core.h @@ -303,7 +303,7 @@ struct smc_link_group { struct workqueue_struct *tx_wq; /* wq for conn. tx workers */ u8 sync_err : 1; /* lgr no longer fits to peer */ u8 terminating : 1;/* lgr is terminating */ - u8 freeing : 1; /* lgr is being freed */ + bool freeing; /* lgr is being freed */ refcount_t refcnt; /* lgr reference count */ bool is_smcd; /* SMC-R or SMC-D */ -- 2.43.0