From nobody Fri Dec 19 10:00:15 2025 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9B8C31E7C34; Tue, 9 Dec 2025 11:24:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765279493; cv=none; b=kxSqWhu5jtLUlkXSb5uUjw18OdkYW5WIRSVDkgAf+9g9CyGomxeb8ur3JHvp322uG4JZMSEPIEtcuU3OnHFrjSp8wLhgO2bn1LPExh8roQrCvEQ1CCoNyOC6MewufXcbeTFqon0OTa/y6Sm8tUE4KkHheDWDWSYax8yHKct6AN8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765279493; c=relaxed/simple; bh=H5btXk/+oC7SAB9++U7/lphBfoew9ALzPNB3wrtQhA4=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=sxXyqu1lMhwYxXPZwU0vIB8ZtAm7zITZjr3SMSan/lIr1lrHHFoIGSgzzXHNBRkTBXBOM5e70kE5/TcLrUaY9S2kmUyNj4dUmVQCZQ4nT2B0daGlCjMwWisqD28GMWc/5/0Ys5GaChvkv/5tcp3K3xG1OqTuWN+6u3gu8YsD7P0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=LGbMT0/4; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=4rBmdu0D; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="LGbMT0/4"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="4rBmdu0D" Date: Tue, 09 Dec 2025 11:24:47 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1765279489; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=sIny6YUQuMC7wj+IntQV/3JJLGsBurBGpsu7lIWtjPs=; b=LGbMT0/4NbkxiYVRKGmNC8gBOBEarw8+VOmsONbuNY7P99bm2GHJ/BvPGfXLEx139Kwnxn f1zNKAh5MkUK8PGKhNij0iy86RVs7lGR/hj5o7FiwpmCD7yEIifyOn1JFkrJKNYbzN5gV7 /4rkLESpISqtx4tpzgqSPCL5kiM0rFHwc+hAE0mhPr45LpqYIGwh8omu+KIUnNpzwURMkR Atvsh3Cq1lL5L5H7lPUZgX9YsrOk8j5NL0F18O1diNYjN0yD5AHpYnUn1cDHTatBCvNgpw m5/MOstIy8cTvoqj36OCAid/F9Jg51mvDU9XGrCeu0PaMv001u3peS8KkVtZSw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1765279489; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=sIny6YUQuMC7wj+IntQV/3JJLGsBurBGpsu7lIWtjPs=; b=4rBmdu0DLQYNYutl74G4xGJ1bnNio0z740uOFQbAigZMbz3KtBehvdtz6cFfBM5nvuUeyZ h2OXDvaIUrpGY4Dw== From: "tip-bot2 for Thaumy Cheng" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: perf/urgent] perf/core: Fix missing read event generation on task exit Cc: Thaumy Cheng , Ingo Molnar , Peter Zijlstra , Adrian Hunter , Alexander Shishkin , Arnaldo Carvalho de Melo , Ian Rogers , James Clark , Jiri Olsa , Mark Rutland , Namhyung Kim , linux-perf-users@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20251209041600.963586-1-thaumy.love@gmail.com> References: <20251209041600.963586-1-thaumy.love@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <176527948706.498.4135909078466502735.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the perf/urgent branch of tip: Commit-ID: c418d8b4d7a43a86b82ee39cb52ece3034383530 Gitweb: https://git.kernel.org/tip/c418d8b4d7a43a86b82ee39cb52ece303= 4383530 Author: Thaumy Cheng AuthorDate: Tue, 09 Dec 2025 12:16:00 +08:00 Committer: Ingo Molnar CommitterDate: Tue, 09 Dec 2025 12:22:25 +01:00 perf/core: Fix missing read event generation on task exit For events with inherit_stat enabled, a "read" event will be generated to collect per task event counts on task exit. The call chain is as follows: do_exit -> perf_event_exit_task -> perf_event_exit_task_context -> perf_event_exit_event -> perf_remove_from_context -> perf_child_detach -> sync_child_event -> perf_event_read_event However, the child event context detaches the task too early in perf_event_exit_task_context, which causes sync_child_event to never generate the read event in this case, since child_event->ctx->task is always set to TASK_TOMBSTONE. Fix that by moving context lock section backward to ensure ctx->task is not set to TASK_TOMBSTONE before generating the read event. Because perf_event_free_task calls perf_event_exit_task_context with exit =3D false to tear down all child events from the context, and the task never lived, accessing the task PID can lead to a use-after-free. To fix that, let sync_child_event read task from argument and move the call to the only place it should be triggered to avoid the effect of setting ctx->task to TASK_TOMESTONE, and add a task parameter to perf_event_exit_event to trigger the sync_child_event properly when needed. This bug can be reproduced by running "perf record -s" and attaching to any program that generates perf events in its child tasks. If we check the result with "perf report -T", the last line of the report will leave an empty table like "# PID TID", which is expected to contain the per-task event counts by design. Fixes: ef54c1a476ae ("perf: Rework perf_event_exit_event()") Signed-off-by: Thaumy Cheng Signed-off-by: Ingo Molnar Acked-by: Peter Zijlstra Cc: Adrian Hunter Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Ian Rogers Cc: James Clark Cc: Jiri Olsa Cc: Mark Rutland Cc: Namhyung Kim Cc: linux-perf-users@vger.kernel.org Link: https://patch.msgid.link/20251209041600.963586-1-thaumy.love@gmail.com --- kernel/events/core.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index ece7168..dad0d3d 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2317,8 +2317,6 @@ out: perf_event__header_size(leader); } =20 -static void sync_child_event(struct perf_event *child_event); - static void perf_child_detach(struct perf_event *event) { struct perf_event *parent_event =3D event->parent; @@ -2337,7 +2335,6 @@ static void perf_child_detach(struct perf_event *even= t) lockdep_assert_held(&parent_event->child_mutex); */ =20 - sync_child_event(event); list_del_init(&event->child_list); } =20 @@ -4588,6 +4585,7 @@ out: static void perf_remove_from_owner(struct perf_event *event); static void perf_event_exit_event(struct perf_event *event, struct perf_event_context *ctx, + struct task_struct *task, bool revoke); =20 /* @@ -4615,7 +4613,7 @@ static void perf_event_remove_on_exec(struct perf_eve= nt_context *ctx) =20 modified =3D true; =20 - perf_event_exit_event(event, ctx, false); + perf_event_exit_event(event, ctx, ctx->task, false); } =20 raw_spin_lock_irqsave(&ctx->lock, flags); @@ -12518,7 +12516,7 @@ static void __pmu_detach_event(struct pmu *pmu, str= uct perf_event *event, /* * De-schedule the event and mark it REVOKED. */ - perf_event_exit_event(event, ctx, true); + perf_event_exit_event(event, ctx, ctx->task, true); =20 /* * All _free_event() bits that rely on event->pmu: @@ -14075,14 +14073,13 @@ void perf_pmu_migrate_context(struct pmu *pmu, in= t src_cpu, int dst_cpu) } EXPORT_SYMBOL_GPL(perf_pmu_migrate_context); =20 -static void sync_child_event(struct perf_event *child_event) +static void sync_child_event(struct perf_event *child_event, + struct task_struct *task) { struct perf_event *parent_event =3D child_event->parent; u64 child_val; =20 if (child_event->attr.inherit_stat) { - struct task_struct *task =3D child_event->ctx->task; - if (task && task !=3D TASK_TOMBSTONE) perf_event_read_event(child_event, task); } @@ -14101,7 +14098,9 @@ static void sync_child_event(struct perf_event *chi= ld_event) =20 static void perf_event_exit_event(struct perf_event *event, - struct perf_event_context *ctx, bool revoke) + struct perf_event_context *ctx, + struct task_struct *task, + bool revoke) { struct perf_event *parent_event =3D event->parent; unsigned long detach_flags =3D DETACH_EXIT; @@ -14124,6 +14123,9 @@ perf_event_exit_event(struct perf_event *event, mutex_lock(&parent_event->child_mutex); /* PERF_ATTACH_ITRACE might be set concurrently */ attach_state =3D READ_ONCE(event->attach_state); + + if (attach_state & PERF_ATTACH_CHILD) + sync_child_event(event, task); } =20 if (revoke) @@ -14215,7 +14217,7 @@ static void perf_event_exit_task_context(struct tas= k_struct *task, bool exit) perf_event_task(task, ctx, 0); =20 list_for_each_entry_safe(child_event, next, &ctx->event_list, event_entry) - perf_event_exit_event(child_event, ctx, false); + perf_event_exit_event(child_event, ctx, exit ? task : NULL, false); =20 mutex_unlock(&ctx->mutex); =20