From nobody Sun Feb 8 11:44:01 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 06ABE18EA2; Sun, 25 Feb 2024 15:17:31 +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=1708874251; cv=none; b=tGKOMcpEOQ57Vg8tn4RPcBmh0tNFMAH5dm+jN+8wa/6RzBIBirr894SW9tWC7m7e622zpKqAeAMns3FDKUDGXwzIYCmghzCIehybhaFXY3eQR+aT83RnnJSJDy07XpUyZ/fvxXtK81Pc/P5mgCYOz31vYCQcuRVLh3avCiTC45s= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708874251; c=relaxed/simple; bh=zY1lZ8MZ8U9F3DpQIB4h84/gioR/3PWPTMDRQesiD6A=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=dWhtF4ClUwELnc+MzOW+vhP+DCslBpAt8xV5xkhpjkoOEO2vK8ZknMq6tDh0/3Q5jXgf4qR5xficpK7ii9+aiwfmpro2nJl5jdtgc0rIWpw6IEXqMFX4zhkq7iO93HEG4WahX43NIgtQ4xhLL5B/gWXD46Do7vC2imvHwOuHdWw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bwkIzM46; 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="bwkIzM46" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 83FB0C433C7; Sun, 25 Feb 2024 15:17:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1708874250; bh=zY1lZ8MZ8U9F3DpQIB4h84/gioR/3PWPTMDRQesiD6A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bwkIzM46UObQsqWkG5HS5vti3Txt9yvE1Fk3VorgTiJd3aDbXosni9JTZajLjwuup JtN1wBLiOnxXL6vcf2tDJpkaMqrtDoYsPeHuISlNEo1QRrbIu5mwHBBoYV2OtQLCLQ 1XetQbQE4jxbXlB+qRYcSUsh0rlSg76sOoXV0omz1g7LFIj9Ew6We2XuP5FdbeyWsl +ku3zLpDcsEqbbcjMXsbJq1K/UalFsfEHqmkkMtuevTMaTCFc7SjDhon+RuKcT/o/M juee10q90x4kdIVYZwIdyaA0PhMuSuu00VE/CPjU9aSa0gRf8I1Y4iiFbWlVkwAlik R7Fvw5lG1i73Q== 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 v8 13/35] function_graph: Use a simple LRU for fgraph_array index number Date: Mon, 26 Feb 2024 00:17:25 +0900 Message-Id: <170887424513.564249.7565785232831569172.stgit@devnote2> X-Mailer: git-send-email 2.34.1 In-Reply-To: <170887410337.564249.6360118840946697039.stgit@devnote2> References: <170887410337.564249.6360118840946697039.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 | 72 +++++++++++++++++++++++++++++++++++----------= ---- 1 file changed, 51 insertions(+), 21 deletions(-) diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c index ae42de909845..da5f269ce718 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 -EBUSY; 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++; @@ -972,6 +1005,8 @@ int register_ftrace_graph(struct fgraph_ops *gops) =20 ret =3D ftrace_startup(&gops->ops, command); out: + if (ret && i >=3D 0) + fgraph_lru_release_index(i); mutex_unlock(&ftrace_lock); return ret; } @@ -979,25 +1014,20 @@ 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--;