Messages in this thread | | | Subject | Re: [RFC PATCH] kernfs: create raw version kernfs_path_len and kernfs_path | From | "Shi, Yang" <> | Date | Fri, 26 Feb 2016 11:37:34 -0800 |
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On 2/26/2016 10:56 AM, Steven Rostedt wrote: > On Fri, 26 Feb 2016 10:15:05 -0800 > Yang Shi <yang.shi@linaro.org> wrote: > >> commit 5634cc2aa9aebc77bc862992e7805469dcf83dac ("writeback: update writeback >> tracepoints to report cgroup") made writeback tracepoints report cgroup >> writeback, but it may trigger the below bug on -rt kernel since kernfs_path >> and kernfs_path_len are called by tracepoints, which acquire sleeping lock. >> >> BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:930 >> in_atomic(): 1, irqs_disabled(): 0, pid: 625, name: kworker/u16:3 >> INFO: lockdep is turned off. >> Preemption disabled at:[<ffffffc000374a5c>] wb_writeback+0xec/0x830 >> >> CPU: 7 PID: 625 Comm: kworker/u16:3 Not tainted 4.4.1-rt5 #20 >> Hardware name: Freescale Layerscape 2085a RDB Board (DT) >> Workqueue: writeback wb_workfn (flush-7:0) >> Call trace: >> [<ffffffc00008d708>] dump_backtrace+0x0/0x200 >> [<ffffffc00008d92c>] show_stack+0x24/0x30 >> [<ffffffc0007b0f40>] dump_stack+0x88/0xa8 >> [<ffffffc000127d74>] ___might_sleep+0x2ec/0x300 >> [<ffffffc000d5d550>] rt_spin_lock+0x38/0xb8 >> [<ffffffc0003e0548>] kernfs_path_len+0x30/0x90 >> [<ffffffc00036b360>] trace_event_raw_event_writeback_work_class+0xe8/0x2e8 >> [<ffffffc000374f90>] wb_writeback+0x620/0x830 >> [<ffffffc000376224>] wb_workfn+0x61c/0x950 >> [<ffffffc000110adc>] process_one_work+0x3ac/0xb30 >> [<ffffffc0001112fc>] worker_thread+0x9c/0x7a8 >> [<ffffffc00011a9e8>] kthread+0x190/0x1b0 >> [<ffffffc000086ca0>] ret_from_fork+0x10/0x30 >> >> Since kernfs_* functions are heavily used by cgroup, so it sounds not >> reasonable to convert kernfs_rename_lock to raw lock. >> >> Create raw version kernfs_path, kernfs_path_len and cgroup_path, which don't >> acquire lock and are used by tracepoints only. >> > > And what prevents name from being freed while the tracepoint is reading > it? > > Perhaps we need this change as well:
Thanks for pointing this out. Yes, it looks we need this since the tracepoints are protected by rcu_read_lock_sched.
Will add this in V2.
Yang
> > -- Steve > > diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c > index 996b7742c90b..d2ef153145c0 100644 > --- a/fs/kernfs/dir.c > +++ b/fs/kernfs/dir.c > @@ -1397,6 +1397,12 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent, > kn->hash = kernfs_name_hash(kn->name, kn->ns); > kernfs_link_sibling(kn); > > + /* > + * Tracepoints may be reading the old name. They are protected > + * by rcu_read_lock_sched(). > + */ > + synchronize_sched(); > + > kernfs_put(old_parent); > kfree_const(old_name); > >
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