Messages in this thread Patch in this message | | | Date | Wed, 15 Feb 2023 16:38:13 -0500 | From | Steven Rostedt <> | Subject | [GIT PULL] tracing: Handle race between rb_move_tail and rb_check_pages |
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Mukesh Ojha <quic_mojha@quicinc.com>
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; }
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