From nobody Mon May 25 15:15:47 2026 X-Original-To: dev-commits-src-all@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 4gPKG11ZsYz6f6xC for ; Mon, 25 May 2026 15:15:53 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "R13" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id 4gPKG06jtxz3m4w for ; Mon, 25 May 2026 15:15:52 +0000 (UTC) (envelope-from git@FreeBSD.org) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=freebsd.org; s=dkim; t=1779722153; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=F/mzrzZZFpnKcYnqTj0CIAH+wF4xA7JLLj5bRFS+tK8=; b=iPEpaXJBOayrJYKb0QBHVS0bFwG6R3dvTiDrYZjgEAzJixPhYcBGF5rhyFBvq4Y169g7mg DoLT8hJ0h2BrBafnETBOb/6kIijLb1pFg4vYyUNwffYuzQcxaHSfZd9wx/GHX/Ryio0J/0 pRwlrV8zizqnChcFAV8afDz09Hub3I2rkDEnEBj/l7M13IlcZtGg+t+QWZikCFthtCXGyL im31JuIoQ6JJdtUkXlh0S2/h5jZbvjtU5sH77fEPFwcmAayuHXql0AbuBBP/YhtlxF0RmL ycKrIgUno+YvtRe++JrYsKBdTBfbD7OjPNOi/ggnchN3sVJlPD5IKbrs4JaQuw== ARC-Seal: i=1; s=dkim; d=freebsd.org; t=1779722153; a=rsa-sha256; cv=none; b=Ky9fIWxIqKTS1foDTfMtO/opWS99SRLjKnkxWZfCzjHsRc7KFAadp0TUw7L3u73liADjqE gYWzFsgU6nR8ZDCVPMvjjgx35jU/z60c+/YKo7Bp/cN4pQkR/fo5N+8Pj7Nzs6HArHsi0y xvmxJuQRjHIAO+Q2H+Nddf3PMdzb1ySNhFqmwwieXiJL8U7iL9ejMKcD10aFM6Xdu5vpmN hmWR3ctZYUBPVTVC8DimQYsuBodfOJLQsC/GzTnJg7HbQJ06Ifa0X6rROIWkmtBtXkQsoP xknJ3O0nXm3xofAL2qnwYGPkHemeLXfRsSR0zr22kI+qz6zHuPQGS49EFS2q9Q== ARC-Authentication-Results: i=1; mx1.freebsd.org; none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=freebsd.org; s=dkim; t=1779722153; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=F/mzrzZZFpnKcYnqTj0CIAH+wF4xA7JLLj5bRFS+tK8=; b=IIQFWICmi0pm8fk0A/mru884X1noRA6lzn+paKY0iuH3K7lM3eu031Gwle9rDizbYi++TZ TL//nyPFHPxqHu3nz7plA70Il2BGeNZXJRLec2Sbgw94OpQLpBpTHFQ8jrHA3hq+GR3+iI hLGFxG6IzQhH/NG3oKe/dsjHJUnPMSiWzTHf/m6W0AEBGAxvmRl98uEv+pULPjkfdvnlVd G9wLRulFYIzJvsAr/x9Te2Lf9XJ6dcw9bkgmiBymvAv5LnNZAlz8bPPW/qh6L9W9pNNP7d 5FCeU/G11ph/GAi2cyILTwC3PaKmtuFEn0t4xTwfnEsSt1ravEIeUJDF1b3WCA== Received: from gitrepo.freebsd.org (gitrepo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:5]) by mxrelay.nyi.freebsd.org (Postfix) with ESMTP id 4gPKG05plWzn34 for ; Mon, 25 May 2026 15:15:52 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from git (uid 1279) (envelope-from git@FreeBSD.org) id 2226e by gitrepo.freebsd.org (DragonFly Mail Agent v0.13+ on gitrepo.freebsd.org); Mon, 25 May 2026 15:15:47 +0000 To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org From: Mark Johnston Subject: git: bc70af0acdda - stable/15 - eventhandler: Fix a race when pruning eventhandlers List-Id: Commit messages for all branches of the src repository List-Archive: https://lists.freebsd.org/archives/dev-commits-src-all List-Help: List-Post: List-Subscribe: List-Unsubscribe: X-BeenThere: dev-commits-src-all@freebsd.org Sender: owner-dev-commits-src-all@FreeBSD.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: markj X-Git-Repository: src X-Git-Refname: refs/heads/stable/15 X-Git-Reftype: branch X-Git-Commit: bc70af0acdda8e9e2a2b21ccc9870f874d803408 Auto-Submitted: auto-generated Date: Mon, 25 May 2026 15:15:47 +0000 Message-Id: <6a1467a3.2226e.53f7bc19@gitrepo.freebsd.org> The branch stable/15 has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=bc70af0acdda8e9e2a2b21ccc9870f874d803408 commit bc70af0acdda8e9e2a2b21ccc9870f874d803408 Author: Mark Johnston AuthorDate: 2026-05-06 11:48:05 +0000 Commit: Mark Johnston CommitDate: 2026-05-25 15:15:39 +0000 eventhandler: Fix a race when pruning eventhandlers By default, eventhandler_deregister() blocks until it reaches some point where no threads are invoking the event. At this point, it knows that 1) no threads are currently executing the handler, 2) some thread has freed the eventhandler structure by virtue of having called eventhandler_prune_list(), so it is safe to return. Suppose a thread is trying to deregister an event handler. A different thread prunes it, and wakes up the first thread. Before the first thread runs, a third thread grabs the event handler lock, and starts executing handlers. The first thread observes el_runcount > 0, and goes back to sleep. The third thread sees no event handlers to prune, and doesn't wake up the first thread, which sleeps forever. This change fixes the race and tries to make eventhandler_invoke() more efficient: keep a count of the number of dead list entries and only prune the list if there is at least one dead entry. Also, in eventhandler_deregister(), we only need to sleep if some dead entries are present, rather than sleeping whenever some thread is running handlers. Reviewed by: kib MFC after: 2 weeks Differential Revision: https://reviews.freebsd.org/D56767 (cherry picked from commit 735b16d490aee158beb54c415b716475a0d19cda) --- sys/kern/subr_eventhandler.c | 18 ++++++++++++++---- sys/sys/eventhandler.h | 4 ++-- 2 files changed, 16 insertions(+), 6 deletions(-) diff --git a/sys/kern/subr_eventhandler.c b/sys/kern/subr_eventhandler.c index 7568101dabd2..e91647648995 100644 --- a/sys/kern/subr_eventhandler.c +++ b/sys/kern/subr_eventhandler.c @@ -198,7 +198,10 @@ _eventhandler_deregister(struct eventhandler_list *list, eventhandler_tag tag, } else { CTR3(KTR_EVH, "%s: marking item %p from \"%s\" as dead", __func__, ep, list->el_name); + KASSERT(ep->ee_priority != EHE_DEAD_PRIORITY, + ("%s: handler for %s is dead", __func__, list->el_name)); ep->ee_priority = EHE_DEAD_PRIORITY; + list->el_deadcount++; } } else { /* remove entire list */ @@ -213,11 +216,15 @@ _eventhandler_deregister(struct eventhandler_list *list, eventhandler_tag tag, } else { CTR2(KTR_EVH, "%s: marking all items from \"%s\" as dead", __func__, list->el_name); - TAILQ_FOREACH(ep, &list->el_entries, ee_link) + TAILQ_FOREACH(ep, &list->el_entries, ee_link) { + KASSERT(ep->ee_priority != EHE_DEAD_PRIORITY, + ("%s: handler for %s is dead", __func__, list->el_name)); ep->ee_priority = EHE_DEAD_PRIORITY; + list->el_deadcount++; + } } } - while (wait && list->el_runcount > 0) + while (wait && list->el_deadcount > 0) mtx_sleep(list, &list->el_lock, 0, "evhrm", 0); EHL_UNLOCK(list); } @@ -292,8 +299,11 @@ eventhandler_prune_list(struct eventhandler_list *list) pruned++; } } - if (pruned > 0) - wakeup(list); + KASSERT(pruned == list->el_deadcount, + ("%s: pruned %u entries from \"%s\" but expected %u", + __func__, pruned, list->el_name, list->el_deadcount)); + list->el_deadcount = 0; + wakeup(list); } /* diff --git a/sys/sys/eventhandler.h b/sys/sys/eventhandler.h index c0d9811dd1b9..2ed71ad1fa98 100644 --- a/sys/sys/eventhandler.h +++ b/sys/sys/eventhandler.h @@ -45,7 +45,7 @@ struct eventhandler_entry_vimage { struct eventhandler_list { char *el_name; - int el_flags; /* Unused. */ + u_int el_deadcount; u_int el_runcount; struct mtx el_lock; TAILQ_ENTRY(eventhandler_list) el_link; @@ -81,7 +81,7 @@ struct eventhandler_list { KASSERT((list)->el_runcount > 0, \ ("eventhandler_invoke: runcount underflow")); \ (list)->el_runcount--; \ - if ((list)->el_runcount == 0) \ + if ((list)->el_runcount == 0 && (list)->el_deadcount != 0) \ eventhandler_prune_list(list); \ EHL_UNLOCK((list)); \ } while (0)