From nobody Fri Feb 13 11:10:48 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 4158C73163; Mon, 15 Apr 2024 12:51:37 +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=1713185498; cv=none; b=NC+xLbwiHwiWHL9AZUNW8lGUnYOSWyH9CLu3iYyUX6458Se3efMz8tkB82kqiNwO8lFitvXc7NzlgUFNAPlshC+ODot4pfzeDj9dq5q+s8nRY92MyokNDl33xl9otYPcUR+oXVjiIbB9+eFf5Mm3nTz1fYdQTi3o7ePYt2yqHV4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713185498; c=relaxed/simple; bh=cyQB+nzI5io0btkPERC0oL8fWVahvmm7TT6YJby8cHk=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=L6M+TPjyUiHP6+2MSPcBqgxsLa45UwWgVy8d+7w4k9FuiQdJJTviZbsuZpKLS3RsMmDjoItQrp9CFf1yhdvyZlkKOu5FIeC4mjOPmRD7wb5DlThZIsV8LLx8mvRs4if/FpFtIlHSsxFG+NKQVlv3j0E85M6jE3jXV/SCJslG6GM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HQqrKs+S; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="HQqrKs+S" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C55D8C113CC; Mon, 15 Apr 2024 12:51:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1713185497; bh=cyQB+nzI5io0btkPERC0oL8fWVahvmm7TT6YJby8cHk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=HQqrKs+SbPbRPha33MJYfsS8cYh/JNlWDMr+fuApxnjLWlu35hVX3FRwI/DeFj3Lr k6gOuFT2c6Y8aLC1XohddWJPGvo4hIN3eVdGeukJlWatSyjI03kqho0MKeHY/8zEWo CoSyxY0UqxuX63R+xsR+CExVduBw2qHwmDKj5RzMuJ4L3qyZjXDdCpYPxlaK0cWeYP qbp+92nJndHb0JldG10xxahYZJ2fBz7gnS90TEllHuCHJA78qMmmqJmWFc3X5sEckN uYxhWg5vDzXghuoLPQp/lB8W1w68AAHRAToGi7U2Wff1DY2VdfasnwpAm1l/khhsLI zvAdmJx1xQC7Q== From: "Masami Hiramatsu (Google)" To: Alexei Starovoitov , Steven Rostedt , Florent Revest Cc: linux-trace-kernel@vger.kernel.org, LKML , Martin KaFai Lau , bpf , Sven Schnelle , Alexei Starovoitov , Jiri Olsa , Arnaldo Carvalho de Melo , Daniel Borkmann , Alan Maguire , Mark Rutland , Peter Zijlstra , Thomas Gleixner , Guo Ren Subject: [PATCH v9 13/36] function_graph: Use a simple LRU for fgraph_array index number Date: Mon, 15 Apr 2024 21:51:31 +0900 Message-Id: <171318549135.254850.10548833007838101346.stgit@devnote2> X-Mailer: git-send-email 2.34.1 In-Reply-To: <171318533841.254850.15841395205784342850.stgit@devnote2> References: <171318533841.254850.15841395205784342850.stgit@devnote2> User-Agent: StGit/0.19 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: quoted-printable From: Masami Hiramatsu (Google) Since the fgraph_array index is used for the bitmap on the shadow stack, it may leave some entries after a function_graph instance is removed. Thus if another instance reuses the fgraph_array index soon after releasing it, the fgraph may confuse to call the newer callback for the entries which are pushed by the older instance. To avoid reusing the fgraph_array index soon after releasing, introduce a simple LRU table for managing the index number. This will reduce the possibility of this confusion. Signed-off-by: Masami Hiramatsu (Google) --- Changes in v8: - Add a WARN_ON_ONCE() if fgraph_lru_table[] is broken when releasing index, and remove WARN_ON_ONCE() from unregister_ftrace_graph() - Fix to release allocated index if register_ftrace_graph() fails. - Add comments and code cleanup. Changes in v5: - Fix the underflow bug in fgraph_lru_release_index() and return 0 if the release is succeded. Changes in v4: - Newly added. --- kernel/trace/fgraph.c | 71 +++++++++++++++++++++++++++++++++++----------= ---- 1 file changed, 50 insertions(+), 21 deletions(-) diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c index aa9a4fac3373..7e73bc3eab8b 100644 --- a/kernel/trace/fgraph.c +++ b/kernel/trace/fgraph.c @@ -99,10 +99,48 @@ enum { DEFINE_STATIC_KEY_FALSE(kill_ftrace_graph); int ftrace_graph_active; =20 -static int fgraph_array_cnt; - static struct fgraph_ops *fgraph_array[FGRAPH_ARRAY_SIZE]; =20 +/* LRU index table for fgraph_array */ +static int fgraph_lru_table[FGRAPH_ARRAY_SIZE]; +static int fgraph_lru_next; +static int fgraph_lru_last; + +/* Initialize fgraph_lru_table with unused index */ +static void fgraph_lru_init(void) +{ + int i; + + for (i =3D 0; i < FGRAPH_ARRAY_SIZE; i++) + fgraph_lru_table[i] =3D i; +} + +/* Release the used index to the LRU table */ +static int fgraph_lru_release_index(int idx) +{ + if (idx < 0 || idx >=3D FGRAPH_ARRAY_SIZE || + WARN_ON_ONCE(fgraph_lru_table[fgraph_lru_last] !=3D -1)) + return -1; + + fgraph_lru_table[fgraph_lru_last] =3D idx; + fgraph_lru_last =3D (fgraph_lru_last + 1) % FGRAPH_ARRAY_SIZE; + return 0; +} + +/* Allocate a new index from LRU table */ +static int fgraph_lru_alloc_index(void) +{ + int idx =3D fgraph_lru_table[fgraph_lru_next]; + + /* No id is available */ + if (idx =3D=3D -1) + return -1; + + fgraph_lru_table[fgraph_lru_next] =3D -1; + fgraph_lru_next =3D (fgraph_lru_next + 1) % FGRAPH_ARRAY_SIZE; + return idx; +} + static inline int get_ret_stack_index(struct task_struct *t, int offset) { return t->ret_stack[offset] & FGRAPH_RET_INDEX_MASK; @@ -367,7 +405,7 @@ int function_graph_enter(unsigned long ret, unsigned lo= ng func, if (index < 0) goto out; =20 - for (i =3D 0; i < fgraph_array_cnt; i++) { + for (i =3D 0; i < FGRAPH_ARRAY_SIZE; i++) { struct fgraph_ops *gops =3D fgraph_array[i]; =20 if (gops =3D=3D &fgraph_stub) @@ -919,7 +957,7 @@ int register_ftrace_graph(struct fgraph_ops *gops) { int command =3D 0; int ret =3D 0; - int i; + int i =3D -1; =20 mutex_lock(&ftrace_lock); =20 @@ -935,21 +973,16 @@ int register_ftrace_graph(struct fgraph_ops *gops) /* The array must always have real data on it */ for (i =3D 0; i < FGRAPH_ARRAY_SIZE; i++) fgraph_array[i] =3D &fgraph_stub; + fgraph_lru_init(); } =20 - /* Look for an available spot */ - for (i =3D 0; i < FGRAPH_ARRAY_SIZE; i++) { - if (fgraph_array[i] =3D=3D &fgraph_stub) - break; - } - if (i >=3D FGRAPH_ARRAY_SIZE) { + i =3D fgraph_lru_alloc_index(); + if (i < 0 || WARN_ON_ONCE(fgraph_array[i] !=3D &fgraph_stub)) { ret =3D -ENOSPC; goto out; } =20 fgraph_array[i] =3D gops; - if (i + 1 > fgraph_array_cnt) - fgraph_array_cnt =3D i + 1; gops->idx =3D i; =20 ftrace_graph_active++; @@ -973,6 +1006,7 @@ int register_ftrace_graph(struct fgraph_ops *gops) if (ret) { fgraph_array[i] =3D &fgraph_stub; ftrace_graph_active--; + fgraph_lru_release_index(i); } out: mutex_unlock(&ftrace_lock); @@ -982,25 +1016,20 @@ int register_ftrace_graph(struct fgraph_ops *gops) void unregister_ftrace_graph(struct fgraph_ops *gops) { int command =3D 0; - int i; =20 mutex_lock(&ftrace_lock); =20 if (unlikely(!ftrace_graph_active)) goto out; =20 - if (unlikely(gops->idx < 0 || gops->idx >=3D fgraph_array_cnt)) + if (unlikely(gops->idx < 0 || gops->idx >=3D FGRAPH_ARRAY_SIZE || + fgraph_array[gops->idx] !=3D gops)) goto out; =20 - WARN_ON_ONCE(fgraph_array[gops->idx] !=3D gops); + if (fgraph_lru_release_index(gops->idx) < 0) + goto out; =20 fgraph_array[gops->idx] =3D &fgraph_stub; - if (gops->idx + 1 =3D=3D fgraph_array_cnt) { - i =3D gops->idx; - while (i >=3D 0 && fgraph_array[i] =3D=3D &fgraph_stub) - i--; - fgraph_array_cnt =3D i + 1; - } =20 ftrace_graph_active--;