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Sat, 05 Sep 2026 17:27:16 -0700 (PDT) From: =?UTF-8?q?=C3=96mer=20Mete=20Kaya?= To: linux-wireless@vger.kernel.org Cc: johannes@sipsolutions.net, kvalo@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, horms@kernel.org, =?UTF-8?q?=C3=96mer=20Mete=20Kaya?= , syzbot+adeb8550754921fece20@syzkaller.appspotmail.com, syzbot+101224300649c3eb8af4@syzkaller.appspotmail.com, syzbot+8141dcbd23a8f857798a@syzkaller.appspotmail.com, syzbot+b0ae8f1abf7d891e0426@syzkaller.appspotmail.com, syzbot+d6bbe0f5705cb8a5aa2b@syzkaller.appspotmail.com Subject: [PATCH] wifi: cfg80211: avoid holding rtnl_mutex across all cfg80211_leave() calls Date: Sun, 6 Sep 2026 03:25:46 +0300 Message-ID: <20260906002657.620076-2-omermetekaya0@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260906002657.620076-1-omermetekaya0@gmail.com> References: <20260903151542.486376-2-omermetekaya0@gmail.com> <20260906002657.620076-1-omermetekaya0@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit reg_check_chans_work() holds rtnl_mutex for the entire duration of iterating over all registered devices and calling cfg80211_leave() on each invalid wdev. cfg80211_leave() can be slow (disconnect, stop AP, leave mesh), causing rtnl_mutex starvation when many wireless interfaces are present. This results in tasks waiting for rtnl_mutex for longer than hung_task_timeout_secs: INFO: task hung in inet_rtm_newaddr INFO: task hung in inet6_rtm_newaddr INFO: task hung in nsim_destroy INFO: task hung in tun_chr_close INFO: task hung in switchdev_deferred_process_work Fix by taking a snapshot of cfg80211_rdev_list under RCU, holding a device reference (get_device/put_device) to prevent freeing, then acquiring rtnl per-device so other rtnl waiters get a chance to run between devices. After acquiring rtnl, wiphy.registered is checked to skip any device that was unregistered in the meantime. Fixes: f7e60032c661 ("wifi: cfg80211: fix locking in regulatory disconnect") Reported-by: syzbot+adeb8550754921fece20@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=adeb8550754921fece20 Reported-by: syzbot+101224300649c3eb8af4@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=101224300649c3eb8af4 Reported-by: syzbot+8141dcbd23a8f857798a@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=8141dcbd23a8f857798a Reported-by: syzbot+b0ae8f1abf7d891e0426@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=b0ae8f1abf7d891e0426 Reported-by: syzbot+d6bbe0f5705cb8a5aa2b@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=d6bbe0f5705cb8a5aa2b Signed-off-by: Ömer Mete Kaya --- net/wireless/reg.c | 44 +++++++++++++++++++++++++++++++++++++++----- 1 file changed, 39 insertions(+), 5 deletions(-) diff --git a/net/wireless/reg.c b/net/wireless/reg.c index a8336baf85dc..7a3f1e470e14 100644 --- a/net/wireless/reg.c +++ b/net/wireless/reg.c @@ -2463,15 +2463,49 @@ static void reg_leave_invalid_chans(struct wiphy *wiphy) static void reg_check_chans_work(struct work_struct *work) { - struct cfg80211_registered_device *rdev; + struct cfg80211_registered_device *rdev, **snap; + int i, n = 0; pr_debug("Verifying active interfaces after reg change\n"); - rtnl_lock(); - for_each_rdev(rdev) - reg_leave_invalid_chans(&rdev->wiphy); + /* + * Snapshot rdev pointers under RCU with a device reference so they + * cannot be freed between per-device rtnl acquisitions. Using a + * per-device rtnl_lock() instead of holding it across all devices + * avoids starving other rtnl waiters when cfg80211_leave() is slow. + */ + rcu_read_lock(); + list_for_each_entry_rcu(rdev, &cfg80211_rdev_list, list) + n++; + rcu_read_unlock(); - rtnl_unlock(); + if (!n) + return; + + snap = kmalloc_array(n, sizeof(*snap), GFP_KERNEL); + if (!snap) + return; + + i = 0; + rcu_read_lock(); + list_for_each_entry_rcu(rdev, &cfg80211_rdev_list, list) { + if (i >= n) + break; + get_device(&rdev->wiphy.dev); + snap[i++] = rdev; + } + rcu_read_unlock(); + n = i; + + for (i = 0; i < n; i++) { + rtnl_lock(); + if (snap[i]->wiphy.registered) + reg_leave_invalid_chans(&snap[i]->wiphy); + rtnl_unlock(); + put_device(&snap[i]->wiphy.dev); + } + + kfree(snap); } void reg_check_channels(void) -- 2.55.0