From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Eric W. Biederman" Date: Wed, 18 May 2022 22:49:50 +0000 Subject: [PATCH 00/16] ptrace: cleanups and calling do_cldstop with only siglock Message-Id: <871qwq5ucx.fsf_-_@email.froward.int.ebiederm.org> List-Id: References: <20220421150248.667412396@infradead.org> <20220421150654.817117821@infradead.org> <87czhap9dy.fsf@email.froward.int.ebiederm.org> <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> <87k0b7v9yk.fsf_-_@email.froward.int.ebiederm.org> <87k0b0apne.fsf_-_@email.froward.int.ebiederm.org> <87a6bv6dl6.fsf_-_@email.froward.int.ebiederm.org> In-Reply-To: <87a6bv6dl6.fsf_-_@email.froward.int.ebiederm.org> (Eric W. Biederman's message of "Thu, 05 May 2022 13:25:57 -0500") MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-kernel@vger.kernel.org Cc: rjw@rjwysocki.net, oleg@redhat.com, mingo@kernel.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de, bigeasy@linutronix.de, Will Deacon , tj@kernel.org, linux-pm@vger.kernel.org, Peter Zijlstra , Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Chris Zankel , Max Filippov , linux-xtensa@linux-xtensa.org, Jann Horn , Kees Cook , linux-ia64@vger.kernel.org, Robert O'Callahan , Kyle Huey , Richard Henderson , Ivan Kokshaysky , Matt Turner , Jason Wessel , Daniel Thompson , Douglas Anderson , Douglas Miller , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras For ptrace_stop to work on PREEMT_RT no spinlocks can be taken once ptrace_freeze_traced has completed successfully. Which fundamentally means the lock dance of dropping siglock and grabbing tasklist_lock does not work on PREEMPT_RT. So I have worked through what is necessary so that tasklist_lock does not need to be grabbed in ptrace_stop after siglock is dropped. I have explored several alternate ways of getting there and along the way I found a lot of small bug fixes/cleanups that don't necessarily contribute to the final result but that or worthwhile on their own. So I have included those changes in this set of changes just so they don't get lost. In addition I had a conversation with Thomas Gleixner recently that emphasized for me the need to reduce the hold times of tasklist_lock, and that made me realize that in principle it is possible. https://lkml.kernel.org/r/87mtfmhap2.fsf@email.froward.int.ebiederm.org Which is a long way of saying that not taking tasklist_lock in ptrace_stop is good not just for PREMPT_RT but also for improving the scalability of the kernel in general. After this set of changes only cgroup_enter_frozen should remain a stumbling block for PREEMPT_RT in the ptrace_stop path. Eric W. Biederman (16): signal/alpha: Remove unused definition of TASK_REAL_PARENT signal/ia64: Remove unused definition of IA64_TASK_REAL_PARENT_OFFSET kdb: Use real_parent when displaying a list of processes powerpc/xmon: Use real_parent when displaying a list of processes ptrace: Remove dead code from __ptrace_detach ptrace: Remove unnecessary locking in ptrace_(get|set)siginfo signal: Wake up the designated parent ptrace: Only populate last_siginfo from ptrace ptrace: In ptrace_setsiginfo deal with invalid si_signo ptrace: In ptrace_signal look at what the debugger did with siginfo ptrace: Use si_sino as the signal number to resume with ptrace: Stop protecting ptrace_set_signr with tasklist_lock ptrace: Document why ptrace_setoptions does not need a lock signal: Protect parent child relationships by childs siglock ptrace: Use siglock instead of tasklist_lock in ptrace_check_attach signal: Always call do_notify_parent_cldstop with siglock held arch/alpha/kernel/asm-offsets.c | 1 - arch/ia64/kernel/asm-offsets.c | 1 - arch/powerpc/xmon/xmon.c | 2 +- kernel/debug/kdb/kdb_main.c | 2 +- kernel/exit.c | 23 +++- kernel/fork.c | 12 +- kernel/ptrace.c | 132 ++++++++---------- kernel/signal.c | 296 ++++++++++++++++++++++++++-------------- 8 files changed, 279 insertions(+), 190 deletions(-) Eric