lkml.org 
[lkml]   [2023]   [Feb]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [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@goodmis.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@quicinc.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@kernel.org>
    > Cc: stable@vger.kernel.org
    > Fixes: 1039221cc278 ("ring-buffer: Do not disable recording when there is an iterator")
    > Reported-by: Zheng Yejian <zhengyejian1@huawei.com>
    > Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
    > Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.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;
    > }
    >

    \
     
     \ /
      Last update: 2023-03-27 00:29    [W:2.260 / U:0.272 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site