On Fri, 2023-09-22 at 10:06 +0100, Anton Ivanov wrote: > On 22/09/2023 09:41, Johannes Berg wrote: > > > Yes, but when does the fork actually happen? > > > > > Looking further at this, now I'm confused as to why it doesn't happen > > _all_ the time. > > > > I think this has pretty much always been wrong, just now we actually > > notice it? > > > > Basically, when we create a new thread (really just mm I think), we say > > the first thing that has to run there is fork_handler(), which > > initialises things the first time around. This calls force_flush_all() > > > > But of course it's called from __schedule(), which has > > preemption/interrupts disabled. So you can't do mmap_read_lock()? > > Stupid question. > > If we have preemption and interrupts disabled and we are UP do we really need > to lock it at this point?
Heh. Functionally, I guess not. But lockdep gets really unhappy about stuff in there: ============================= WARNING: suspicious RCU usage 6.6.0-rc1 #159 Not tainted ----------------------------- lib/maple_tree.c:840 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 no locks held by startup.sh/282. stack backtrace: CPU: 0 PID: 282 Comm: startup.sh Not tainted 6.6.0-rc1 #159 Stack: 71a9bdd0 605001f3 00000000 6003cf40 606bd782 00000000 60b3e968 00000000 71a9be10 60526292 00000082 6051cb2a Call Trace: [<6051cb2a>] ? _printk+0x0/0x94 [<6002a5b4>] show_stack+0x13d/0x14c [<605001f3>] ? dump_stack_print_info+0xde/0xed [<6003cf40>] ? um_set_signals+0x0/0x3f [<60526292>] dump_stack_lvl+0x62/0x96 [<6051cb2a>] ? _printk+0x0/0x94 [<605262e0>] dump_stack+0x1a/0x1c [<6008865e>] lockdep_rcu_suspicious+0x10d/0x11c [<6052721b>] ? debug_lockdep_rcu_enabled+0x0/0x3b [<6052721b>] ? debug_lockdep_rcu_enabled+0x0/0x3b [<605085cd>] mas_root+0x86/0x91 [<60508547>] ? mas_root+0x0/0x91 [<60508611>] mas_start+0x39/0x9c [<60508875>] ? mas_state_walk+0x0/0x3e [<6050888d>] mas_state_walk+0x18/0x3e [<605088f1>] mas_walk+0x3e/0x96 [<60508a03>] mas_find_setup+0xba/0xcd [<60509d49>] ? mas_find+0x0/0x4a [<60509d71>] mas_find+0x28/0x4a [<6002c92b>] force_flush_all+0x51/0x7c [<6002926e>] fork_handler+0x14/0x96 johannes _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um
