From nobody Sun Feb 8 16:32:17 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 C8E8518EFD0; Thu, 8 Aug 2024 14:21:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723126883; cv=none; b=RGwjXX3IfOWsd64Noy/bqwyxu6pa19WZKS9VePP6uHaavsMeMgDoiDY+IUvHO+1oTpjoLRM5gTgkL7Y/iajUikSuTEHgk/ZzWrnLmRgiCgWW/kgtdyUBOc5h7bIePdwjx+VhJiq9j/FC/dSVTPmmNZZvF0d8huzk5mVFEg9kKdk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723126883; c=relaxed/simple; bh=6CF9RCJDSG9WwrjbP/VpGfJzbbGCBQl6aRvx0RgXNkA=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=MtkL5OXLW5N3Kt2F2Deucd9v3uOirBjzQ7fx7khZ4gGpzqe/8umLCWHQ+VbtC6JTCdNJNfwACje7S16CMjT7T/pmUhz6XV01mmk5gp8eOocgK/atcdZp1aXEmd2VednMbK5GweZOsa4floByGorDyVEDBMAusCTTHkV80bos94o= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id B4CE3C4AF10; Thu, 8 Aug 2024 14:21:23 +0000 (UTC) Received: from rostedt by gandalf with local (Exim 4.98) (envelope-from ) id 1sc416-00000000BSz-2rFy; Thu, 08 Aug 2024 10:21:24 -0400 Message-ID: <20240808142124.542872106@goodmis.org> User-Agent: quilt/0.68 Date: Thu, 08 Aug 2024 10:20:44 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , stable@vger.kernel.org, Cheng-Jui Wang , Tze-nan Wu Subject: [for-linus][PATCH 7/9] tracing: Fix overflow in get_free_elt() References: <20240808142037.495820579@goodmis.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Tze-nan Wu "tracing_map->next_elt" in get_free_elt() is at risk of overflowing. Once it overflows, new elements can still be inserted into the tracing_map even though the maximum number of elements (`max_elts`) has been reached. Continuing to insert elements after the overflow could result in the tracing_map containing "tracing_map->max_size" elements, leaving no empty entries. If any attempt is made to insert an element into a full tracing_map using `__tracing_map_insert()`, it will cause an infinite loop with preemption disabled, leading to a CPU hang problem. Fix this by preventing any further increments to "tracing_map->next_elt" once it reaches "tracing_map->max_elt". Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Fixes: 08d43a5fa063e ("tracing: Add lock-free tracing_map") Co-developed-by: Cheng-Jui Wang Link: https://lore.kernel.org/20240805055922.6277-1-Tze-nan.Wu@mediatek.com Signed-off-by: Cheng-Jui Wang Signed-off-by: Tze-nan Wu Signed-off-by: Steven Rostedt (Google) --- kernel/trace/tracing_map.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/trace/tracing_map.c b/kernel/trace/tracing_map.c index a4dcf0f24352..3a56e7c8aa4f 100644 --- a/kernel/trace/tracing_map.c +++ b/kernel/trace/tracing_map.c @@ -454,7 +454,7 @@ static struct tracing_map_elt *get_free_elt(struct trac= ing_map *map) struct tracing_map_elt *elt =3D NULL; int idx; =20 - idx =3D atomic_inc_return(&map->next_elt); + idx =3D atomic_fetch_add_unless(&map->next_elt, 1, map->max_elts); if (idx < map->max_elts) { elt =3D *(TRACING_MAP_ELT(map->elts, idx)); if (map->ops && map->ops->elt_init) @@ -699,7 +699,7 @@ void tracing_map_clear(struct tracing_map *map) { unsigned int i; =20 - atomic_set(&map->next_elt, -1); + atomic_set(&map->next_elt, 0); atomic64_set(&map->hits, 0); atomic64_set(&map->drops, 0); =20 @@ -783,7 +783,7 @@ struct tracing_map *tracing_map_create(unsigned int map= _bits, =20 map->map_bits =3D map_bits; map->max_elts =3D (1 << map_bits); - atomic_set(&map->next_elt, -1); + atomic_set(&map->next_elt, 0); =20 map->map_size =3D (1 << (map_bits + 1)); map->ops =3D ops; --=20 2.43.0