Messages in this thread | | | From | Marco Elver <> | Date | Wed, 17 Aug 2022 15:14:54 +0200 | Subject | Re: [PATCH v3 11/14] perf/hw_breakpoint: Reduce contention with large number of tasks |
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On Wed, 17 Aug 2022 at 15:03, Peter Zijlstra <peterz@infradead.org> wrote: > > On Mon, Jul 04, 2022 at 05:05:11PM +0200, Marco Elver wrote: > > +static bool bp_constraints_is_locked(struct perf_event *bp) > > +{ > > + struct mutex *tsk_mtx = get_task_bps_mutex(bp); > > + > > + return percpu_is_write_locked(&bp_cpuinfo_sem) || > > + (tsk_mtx ? mutex_is_locked(tsk_mtx) : > > + percpu_is_read_locked(&bp_cpuinfo_sem)); > > +} > > > @@ -426,18 +521,28 @@ static int modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type) > > */ > > int dbg_reserve_bp_slot(struct perf_event *bp) > > { > > - if (mutex_is_locked(&nr_bp_mutex)) > > + int ret; > > + > > + if (bp_constraints_is_locked(bp)) > > return -1; > > > > - return __reserve_bp_slot(bp, bp->attr.bp_type); > > + /* Locks aren't held; disable lockdep assert checking. */ > > + lockdep_off(); > > + ret = __reserve_bp_slot(bp, bp->attr.bp_type); > > + lockdep_on(); > > + > > + return ret; > > } > > > > int dbg_release_bp_slot(struct perf_event *bp) > > { > > - if (mutex_is_locked(&nr_bp_mutex)) > > + if (bp_constraints_is_locked(bp)) > > return -1; > > > > + /* Locks aren't held; disable lockdep assert checking. */ > > + lockdep_off(); > > __release_bp_slot(bp, bp->attr.bp_type); > > + lockdep_on(); > > > > return 0; > > } > > Urggghhhh... this is horrible crap. That is, the current code is that > and this makes it worse :/
Heh, yes and when I looked at it I really wanted to see if it can change. But from what I can tell, when the kernel debugger is being attached, the kernel does stop everything it does and we need the horrible thing above to not deadlock. And these dbg_ functions are not normally used, so I decided to leave it as-is. Suggestions?
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