Messages in this thread | | | From | "Eric W. Biederman" <> | Date | Fri, 20 May 2022 14:32:24 -0500 | Subject | Re: [PATCH 00/16] ptrace: cleanups and calling do_cldstop with only siglock |
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Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:
> On 2022-05-18 17:49:50 [-0500], Eric W. Biederman wrote: >> >> 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. > … > It took me a while to realise that this is a follow-up I somehow assumed > that you added a few patches on top. Might have been the yesterday's > heat. b4 also refused to download this series because the v4 in this > thread looked newer… Anyway. Both series applied: > > | ============================= > | WARNING: suspicious RCU usage > | 5.18.0-rc7+ #16 Not tainted > | ----------------------------- > | include/linux/ptrace.h:120 suspicious rcu_dereference_check() usage! > | > | other info that might help us debug this: > | > | rcu_scheduler_active = 2, debug_locks = 1 > | 2 locks held by ssdd/1734: > | #0: ffff88800eaa6918 (&sighand->siglock){....}-{2:2}, at: lock_parents_siglocks+0xf0/0x3b0 > | #1: ffff88800eaa71d8 (&sighand->siglock/2){....}-{2:2}, at: lock_parents_siglocks+0x115/0x3b0 > | > | stack backtrace: > | CPU: 2 PID: 1734 Comm: ssdd Not tainted 5.18.0-rc7+ #16 > | Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.0-debian-1.16.0-4 04/01/2014 > | Call Trace: > | <TASK> > | dump_stack_lvl+0x45/0x5a > | unlock_parents_siglocks+0xb6/0xc0 > | ptrace_stop+0xb9/0x390 > | get_signal+0x51c/0x8d0 > | arch_do_signal_or_restart+0x31/0x750 > | exit_to_user_mode_prepare+0x157/0x220 > | irqentry_exit_to_user_mode+0x5/0x50 > | asm_sysvec_apic_timer_interrupt+0x12/0x20 > > That is ptrace_parent() in unlock_parents_siglocks().
How odd. I thought I had the appropriate lockdep config options enabled in my test build to catch things like this. I guess not.
Now I am trying to think how to tell it that holding the appropriate iglock makes this ok.
Eric
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