Messages in this thread | | | From | Marco Elver <> | Date | Mon, 29 Aug 2022 11:38:22 +0200 | Subject | Re: [PATCH v3 11/14] perf/hw_breakpoint: Reduce contention with large number of tasks |
| |
On Mon, 29 Aug 2022 at 10:38, Peter Zijlstra <peterz@infradead.org> wrote: > > On Wed, Aug 17, 2022 at 03:14:54PM +0200, Marco Elver wrote: > > 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? > > What context is this ran in? NMI should already have lockdep disabled.
kgdb can enter via kgdb_nmicall*() but also via kgdb_handle_exception(), which isn't for NMI.
| |