From nobody Fri May 29 20:57:41 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 4gRwff6nhwz6g5qL for ; Fri, 29 May 2026 20:57:46 +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 4gRwff5YGhz44Sv for ; Fri, 29 May 2026 20:57:46 +0000 (UTC) (envelope-from git@FreeBSD.org) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=freebsd.org; s=dkim; t=1780088266; 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=n/kSZAM/W3C0wk8a6tSqVcxAkOpSaL2qNbI/P/nNmnE=; b=V50BjyUnT+kpTmYfu2RZhoJjEDeGvUoBWK7Db/kFjyiELPYKkKocl1S43NdxLCjZkaK6CY qGPZ5q+gHU0f1rEN1GpiXKJb+Fl0gaJHnBtoQXE23jk9zY5FfT3Jz2G12fHSHdGOwkFFAn DYglXdq1gO4lW2a8HX1T4IifLf1ykSVW/aBxNdWUXNIPeuNUCme1byc17gBlzTtbxhdr6G mOS1nAvz025wKFCPtwIPwrfuditY64011bIVEnchdLFNo2AtKRQHhVvfN2w2ks1VJqJ2o/ ZtNZQW5bEfLFkC0WKKNQRcK/QDKkTt7RbxeBBuhaMlwlOiQfGKNC5+LEE3Sfcg== ARC-Seal: i=1; s=dkim; d=freebsd.org; t=1780088266; a=rsa-sha256; cv=none; b=oVMcRHRisAE5f7mNj1/3TMY4Z8IQXrGlx9MNBmcCYdhWQGcer1d5H8VvTGAT2nl1Z/FZKW 76FvMHWJXXQcPXC8BGdPUCQvA4CH6ydhsVoHPyMT1gvEJY86pMT6OXgXgAL5TLLzqa7q6C FliLtYi4qwaPFK8yyc+CQt3mIN81mofcqC6ag7dH0hCAYKmGzX2VmNgscSBLJpujtBy+CK nwP5Sh24dzVR7OMjW3Pvjx6nT1Lb0KGxW/odPvKGszxGpOcYsG29C+MMI/FN4X3CmeKws0 QzjQx740sSliV1Mk4D9Lc7Nh5H3+B6Vr8suHRfSYyGx0ED8MWDeBrRN8del20w== 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=1780088266; 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=n/kSZAM/W3C0wk8a6tSqVcxAkOpSaL2qNbI/P/nNmnE=; b=CHp05Q36WrN2mljLJ/uOhJyIBVbEnK//YiTEpv1L+9/eUCSFWeJ1p2fh49YaeIdEKa3UFG 38Yaccuwp9GdFZUK+c/FVETf10L0M0AGZWMOtdZRuUBLeBP2GWAsS/vLPnzgNGvV14scFz +j+8SfBNiprnijRZAgfc95F4RVY658DcHCoTVrl2qJh2REWyOTDjkpBcxi44S9/ad+7TyG phFKCLRB29E1WjuI0yV9suV/y0zOC3RHytesHormBlPTlF0xNCNvJpOalxy3DpqekRS9+w c1NQ74Lw+2y3/xFGVwFTI3RYVxo7AVyxd1LA+eR2gVktsZsIbegNbIge7tdBHw== Received: from gitrepo.freebsd.org (gitrepo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:5]) by mxrelay.nyi.freebsd.org (Postfix) with ESMTP id 4gRwff51YGzqPf for ; Fri, 29 May 2026 20:57:46 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from git (uid 1279) (envelope-from git@FreeBSD.org) id 3460f by gitrepo.freebsd.org (DragonFly Mail Agent v0.13+ on gitrepo.freebsd.org); Fri, 29 May 2026 20:57:41 +0000 To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org From: Mark Johnston Subject: git: 4a875b186e8d - stable/14 - 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/14 X-Git-Reftype: branch X-Git-Commit: 4a875b186e8d53e38f79a9e4c0e9ed8949e38ed7 Auto-Submitted: auto-generated Date: Fri, 29 May 2026 20:57:41 +0000 Message-Id: <6a19fdc5.3460f.f44f774@gitrepo.freebsd.org> The branch stable/14 has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=4a875b186e8d53e38f79a9e4c0e9ed8949e38ed7 commit 4a875b186e8d53e38f79a9e4c0e9ed8949e38ed7 Author: Mark Johnston AuthorDate: 2026-05-06 11:48:05 +0000 Commit: Mark Johnston CommitDate: 2026-05-29 19:44:43 +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 5a5365d0be6e..ccbb07b826b8 100644 --- a/sys/kern/subr_eventhandler.c +++ b/sys/kern/subr_eventhandler.c @@ -199,7 +199,10 @@ _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 */ @@ -214,11 +217,15 @@ _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); } @@ -293,8 +300,11 @@ 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 47024ecf87a9..be1b04606320 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)