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Date: Mon, 20 Feb 2023 15:50:35 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Mukesh Ojha <quic_mojha@...cinc.com>
Subject: Re: [GIT PULL] tracing: Handle race between rb_move_tail and
rb_check_pages
Linus,
I was wondering why this never got pulled, and then realized that I never
added you to the "To" line :-p
-- Steve
On Wed, 15 Feb 2023 16:38:13 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:
> Linus,
>
> tracing: Fix race that causes a warning of corrupt ring buffer
>
> With the change that allows to read the "trace" file without disabling
> writing to the ring buffer, there was an integrity check of the ring
> buffer in the iterator read code, that expected the ring buffer to be
> write disabled. This caused the integrity check to trigger when stress
> reading the "trace" file while writing was happening.
>
> The integrity check is a bit aggressive (and has never triggered in
> practice). Change it so that it checks just the integrity of the linked
> pages without clearing the flags inside the pointers. This removes the
> warning that was being triggered.
>
> Note, this was added on top of my last pull request here:
>
> https://lore.kernel.org/lkml/20230213100836.33d2b0b0@rorschach.local.home/
>
> Please pull the latest trace-v6.2-rc7-3 tree, which can be found at:
>
>
> git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
> trace-v6.2-rc7-3
>
> Tag SHA1: cae6c6648a7a9c3a52d1aa5f7beeee9b19a9f059
> Head SHA1: 8843e06f67b14f71c044bf6267b2387784c7e198
>
>
> Mukesh Ojha (1):
> ring-buffer: Handle race between rb_move_tail and rb_check_pages
>
> ----
> kernel/trace/ring_buffer.c | 42 ++++++++++--------------------------------
> 1 file changed, 10 insertions(+), 32 deletions(-)
> ---------------------------
> commit 8843e06f67b14f71c044bf6267b2387784c7e198
> Author: Mukesh Ojha <quic_mojha@...cinc.com>
> Date: Tue Feb 14 17:36:43 2023 +0530
>
> ring-buffer: Handle race between rb_move_tail and rb_check_pages
>
> It seems a data race between ring_buffer writing and integrity check.
> That is, RB_FLAG of head_page is been updating, while at same time
> RB_FLAG was cleared when doing integrity check rb_check_pages():
>
> rb_check_pages() rb_handle_head_page():
> -------- --------
> rb_head_page_deactivate()
> rb_head_page_set_normal()
> rb_head_page_activate()
>
> We do intergrity test of the list to check if the list is corrupted and
> it is still worth doing it. So, let's refactor rb_check_pages() such that
> we no longer clear and set flag during the list sanity checking.
>
> [1] and [2] are the test to reproduce and the crash report respectively.
>
> 1:
> ``` read_trace.sh
> while true;
> do
> # the "trace" file is closed after read
> head -1 /sys/kernel/tracing/trace > /dev/null
> done
> ```
> ``` repro.sh
> sysctl -w kernel.panic_on_warn=1
> # function tracer will writing enough data into ring_buffer
> echo function > /sys/kernel/tracing/current_tracer
> ./read_trace.sh &
> ./read_trace.sh &
> ./read_trace.sh &
> ./read_trace.sh &
> ./read_trace.sh &
> ./read_trace.sh &
> ./read_trace.sh &
> ./read_trace.sh &
> ```
>
> 2:
> ------------[ cut here ]------------
> WARNING: CPU: 9 PID: 62 at kernel/trace/ring_buffer.c:2653
> rb_move_tail+0x450/0x470
> Modules linked in:
> CPU: 9 PID: 62 Comm: ksoftirqd/9 Tainted: G W 6.2.0-rc6+
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
> RIP: 0010:rb_move_tail+0x450/0x470
> Code: ff ff 4c 89 c8 f0 4d 0f b1 02 48 89 c2 48 83 e2 fc 49 39 d0 75 24
> 83 e0 03 83 f8 02 0f 84 e1 fb ff ff 48 8b 57 10 f0 ff 42 08 <0f> 0b 83
> f8 02 0f 84 ce fb ff ff e9 db
> RSP: 0018:ffffb5564089bd00 EFLAGS: 00000203
> RAX: 0000000000000000 RBX: ffff9db385a2bf81 RCX: ffffb5564089bd18
> RDX: ffff9db281110100 RSI: 0000000000000fe4 RDI: ffff9db380145400
> RBP: ffff9db385a2bf80 R08: ffff9db385a2bfc0 R09: ffff9db385a2bfc2
> R10: ffff9db385a6c000 R11: ffff9db385a2bf80 R12: 0000000000000000
> R13: 00000000000003e8 R14: ffff9db281110100 R15: ffffffffbb006108
> FS: 0000000000000000(0000) GS:ffff9db3bdcc0000(0000)
> knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005602323024c8 CR3: 0000000022e0c000 CR4: 00000000000006e0
> Call Trace:
> <TASK>
> ring_buffer_lock_reserve+0x136/0x360
> ? __do_softirq+0x287/0x2df
> ? __pfx_rcu_softirq_qs+0x10/0x10
> trace_function+0x21/0x110
> ? __pfx_rcu_softirq_qs+0x10/0x10
> ? __do_softirq+0x287/0x2df
> function_trace_call+0xf6/0x120
> 0xffffffffc038f097
> ? rcu_softirq_qs+0x5/0x140
> rcu_softirq_qs+0x5/0x140
> __do_softirq+0x287/0x2df
> run_ksoftirqd+0x2a/0x30
> smpboot_thread_fn+0x188/0x220
> ? __pfx_smpboot_thread_fn+0x10/0x10
> kthread+0xe7/0x110
> ? __pfx_kthread+0x10/0x10
> ret_from_fork+0x2c/0x50
> </TASK>
> ---[ end trace 0000000000000000 ]---
>
> [ crash report and test reproducer credit goes to Zheng Yejian]
>
> Link: https://lore.kernel.org/linux-trace-kernel/1676376403-16462-1-git-send-email-quic_mojha@quicinc.com
>
> Cc: <mhiramat@...nel.org>
> Cc: stable@...r.kernel.org
> Fixes: 1039221cc278 ("ring-buffer: Do not disable recording when there is an iterator")
> Reported-by: Zheng Yejian <zhengyejian1@...wei.com>
> Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
>
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index c366a0a9ddba..b641cab2745e 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1580,19 +1580,6 @@ static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
> return 0;
> }
>
> -/**
> - * rb_check_list - make sure a pointer to a list has the last bits zero
> - */
> -static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
> - struct list_head *list)
> -{
> - if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
> - return 1;
> - if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
> - return 1;
> - return 0;
> -}
> -
> /**
> * rb_check_pages - integrity check of buffer pages
> * @cpu_buffer: CPU buffer with pages to test
> @@ -1602,36 +1589,27 @@ static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
> */
> static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
> {
> - struct list_head *head = cpu_buffer->pages;
> - struct buffer_page *bpage, *tmp;
> + struct list_head *head = rb_list_head(cpu_buffer->pages);
> + struct list_head *tmp;
>
> - /* Reset the head page if it exists */
> - if (cpu_buffer->head_page)
> - rb_set_head_page(cpu_buffer);
> -
> - rb_head_page_deactivate(cpu_buffer);
> -
> - if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
> - return -1;
> - if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
> + if (RB_WARN_ON(cpu_buffer,
> + rb_list_head(rb_list_head(head->next)->prev) != head))
> return -1;
>
> - if (rb_check_list(cpu_buffer, head))
> + if (RB_WARN_ON(cpu_buffer,
> + rb_list_head(rb_list_head(head->prev)->next) != head))
> return -1;
>
> - list_for_each_entry_safe(bpage, tmp, head, list) {
> + for (tmp = rb_list_head(head->next); tmp != head; tmp = rb_list_head(tmp->next)) {
> if (RB_WARN_ON(cpu_buffer,
> - bpage->list.next->prev != &bpage->list))
> + rb_list_head(rb_list_head(tmp->next)->prev) != tmp))
> return -1;
> +
> if (RB_WARN_ON(cpu_buffer,
> - bpage->list.prev->next != &bpage->list))
> - return -1;
> - if (rb_check_list(cpu_buffer, &bpage->list))
> + rb_list_head(rb_list_head(tmp->prev)->next) != tmp))
> return -1;
> }
>
> - rb_head_page_activate(cpu_buffer);
> -
> return 0;
> }
>
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