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From: Al Viro <viro@zeniv.linux.org.uk>
To: Hao Luo <haoluo@google.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>, KP Singh <kpsingh@kernel.org>,
	Shakeel Butt <shakeelb@google.com>,
	Joe Burton <jevburton.kernel@gmail.com>,
	Tejun Heo <tj@kernel.org>,
	joshdon@google.com, sdf@google.com, bpf@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf-next v1 1/9] bpf: Add mkdir, rmdir, unlink syscalls for prog_bpf_syscall
Date: Mon, 14 Mar 2022 23:10:33 +0000	[thread overview]
Message-ID: <Yi/LaZ5id4ZjqFmL@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <CA+khW7g+T2sAkP1aycmts_82JKWgYk5Y0ZJp+EvjFUyNY8W_5w@mail.gmail.com>

On Mon, Mar 14, 2022 at 10:07:31AM -0700, Hao Luo wrote:
> Hello Al,

> > In which contexts can those be called?
> >
> 
> In a sleepable context. The plan is to introduce a certain tracepoints
> as sleepable, a program that attaches to sleepable tracepoints is
> allowed to call these functions. In particular, the first sleepable
> tracepoint introduced in this patchset is one at the end of
> cgroup_mkdir(). Do you have any advices?

Yes - don't do it, unless you really want a lot of user-triggerable
deadlocks.

Pathname resolution is not locking-agnostic.  In particular, you can't
do it if you are under any ->i_rwsem, whether it's shared or exclusive.
That includes cgroup_mkdir() callchains.  And if the pathname passed
to these functions will have you walk through the parent directory,
you would get screwed (e.g. if the next component happens to be
inexistent, triggering a lookup, which takes ->i_rwsem shared).

  reply	other threads:[~2022-03-14 23:37 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-25 23:43 [PATCH bpf-next v1 0/9] Extend cgroup interface with bpf Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 1/9] bpf: Add mkdir, rmdir, unlink syscalls for prog_bpf_syscall Hao Luo
2022-02-27  5:18   ` Kumar Kartikeya Dwivedi
2022-02-28 22:10     ` Hao Luo
2022-03-02 19:34       ` Alexei Starovoitov
2022-03-03 18:50         ` Hao Luo
2022-03-04 18:37           ` Hao Luo
2022-03-05 23:47             ` Alexei Starovoitov
2022-03-08 21:08               ` Hao Luo
2022-03-02 20:55   ` Yonghong Song
2022-03-03 18:56     ` Hao Luo
2022-03-03 19:13       ` Yonghong Song
2022-03-03 19:15         ` Hao Luo
2022-03-12  3:46   ` Al Viro
2022-03-14 17:07     ` Hao Luo
2022-03-14 23:10       ` Al Viro [this message]
2022-03-15 17:27         ` Hao Luo
2022-03-15 18:59           ` Alexei Starovoitov
2022-03-15 19:03             ` Alexei Starovoitov
2022-03-15 19:00           ` Al Viro
2022-03-15 19:47             ` Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 2/9] bpf: Add BPF_OBJ_PIN and BPF_OBJ_GET in the bpf_sys_bpf helper Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 3/9] selftests/bpf: tests mkdir, rmdir, unlink and pin in syscall Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 4/9] bpf: Introduce sleepable tracepoints Hao Luo
2022-03-02 19:41   ` Alexei Starovoitov
2022-03-03 19:37     ` Hao Luo
2022-03-03 19:59       ` Alexei Starovoitov
2022-03-02 21:23   ` Yonghong Song
2022-03-02 21:30     ` Alexei Starovoitov
2022-03-03  1:08       ` Yonghong Song
2022-03-03  2:29         ` Alexei Starovoitov
2022-03-03 19:43           ` Hao Luo
2022-03-03 20:02             ` Alexei Starovoitov
2022-03-03 20:04               ` Alexei Starovoitov
2022-03-03 22:06                 ` Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 5/9] cgroup: Sleepable cgroup tracepoints Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 6/9] libbpf: Add sleepable tp_btf Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 7/9] bpf: Lift permission check in __sys_bpf when called from kernel Hao Luo
2022-03-02 20:01   ` Alexei Starovoitov
2022-03-03 19:14     ` Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 8/9] bpf: Introduce cgroup iter Hao Luo
2022-02-26  2:32   ` kernel test robot
2022-02-26  2:32   ` kernel test robot
2022-02-26  2:53   ` kernel test robot
2022-03-02 21:59   ` Yonghong Song
2022-03-03 20:02     ` Hao Luo
2022-03-02 22:45   ` Kumar Kartikeya Dwivedi
2022-03-03  2:03     ` Yonghong Song
2022-03-03  3:03       ` Kumar Kartikeya Dwivedi
2022-03-03  4:00         ` Alexei Starovoitov
2022-03-03  7:33         ` Yonghong Song
2022-03-03  8:13           ` Kumar Kartikeya Dwivedi
2022-03-03 21:52           ` Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 9/9] selftests/bpf: Tests using sleepable tracepoints to monitor cgroup events Hao Luo

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