From: Thomas Gleixner <tglx@linutronix.de>
To: Dmitrii Banshchikov <me@ubique.spb.ru>,
Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: syzbot <syzbot+43fd005b5a1b4d10781e@syzkaller.appspotmail.com>,
John Stultz <john.stultz@linaro.org>,
LKML <linux-kernel@vger.kernel.org>,
sboyd@kernel.org,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Peter Zijlstra <peterz@infradead.org>,
Mark Rutland <mark.rutland@arm.com>,
Steven Rostedt <rosted@goodmis.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>, bpf <bpf@vger.kernel.org>
Subject: Re: [syzbot] possible deadlock in ktime_get_coarse_ts64
Date: Fri, 05 Nov 2021 18:24:30 +0100 [thread overview]
Message-ID: <875yt64isx.ffs@tglx> (raw)
In-Reply-To: <20211105170328.fjnzr6bnbca7mdfq@amnesia>
On Fri, Nov 05 2021 at 21:03, Dmitrii Banshchikov wrote:
> On Fri, Nov 05, 2021 at 08:53:06AM -0700, Alexei Starovoitov wrote:
>> > Timestamps from within a tracepoint can only be taken with:
>> >
>> > 1) jiffies
>> > 2) sched_clock()
>> > 3) ktime_get_*_fast_ns()
>> >
>> > Those are NMI safe and can be invoked from anywhere.
>> >
>> > All other time getters which have to use the timekeeping seqcount
>> > protection are prone to live locks and _cannot_ be used from
>> > tracepoints ever.
>>
>> Obviously.
>> That helper was added for networking use cases and accidentally
>> enabled for tracing.
>
> Sorry for that.
> I'm preparing a patch that will forbid using bpf_ktime_get_coarse_ns()
> helper in BPF_LINK_TYPE_RAW_TRACEPOINT.
It cannot be used in TRACING and PERF_EVENT either. But those contexts
have to exclude other functions as well:
bpf_ktime_get_ns
bpf_ktime_get_boot_ns
along with
bpf_spin_lock/unlock
bpf_timer_*
Thanks,
tglx
next prev parent reply other threads:[~2021-11-05 17:24 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-04 16:18 [syzbot] possible deadlock in ktime_get_coarse_ts64 syzbot
2021-11-05 13:10 ` Thomas Gleixner
2021-11-05 13:21 ` Steven Rostedt
2021-11-05 15:53 ` Alexei Starovoitov
2021-11-05 17:03 ` Dmitrii Banshchikov
2021-11-05 17:24 ` Thomas Gleixner [this message]
2021-11-06 20:07 ` Dmitrii Banshchikov
2021-11-07 10:32 ` Thomas Gleixner
2021-11-07 13:51 ` Dmitrii Banshchikov
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