On Tue, Sep 07, 2021 at 03:20:44PM +0200, Maarten Lankhorst wrote: > i915 will soon gain an eviction path that trylock a whole lot of locks > for eviction, getting dmesg failures like below: > > BUG: MAX_LOCK_DEPTH too low! > turning off the locking correctness validator. > depth: 48 max: 48! > 48 locks held by i915_selftest/5776: > #0: ffff888101a79240 (&dev->mutex){....}-{3:3}, at: __driver_attach+0x88/0x160 > #1: ffffc900009778c0 (reservation_ww_class_acquire){+.+.}-{0:0}, at: i915_vma_pin.constprop.63+0x39/0x1b0 [i915] > #2: ffff88800cf74de8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_vma_pin.constprop.63+0x5f/0x1b0 [i915] > #3: ffff88810c7f9e38 (&vm->mutex/1){+.+.}-{3:3}, at: i915_vma_pin_ww+0x1c4/0x9d0 [i915] > #4: ffff88810bad5768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] > #5: ffff88810bad60e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] > ... > #46: ffff88811964d768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] > #47: ffff88811964e0e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] > INFO: lockdep is turned off. > As an intermediate solution, add an acquire context to ww_mutex_trylock, > which allows us to do proper nesting annotations on the trylocks, making > the above lockdep splat disappear. Fair enough I suppose. > +/** > + * ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context > + * @lock: mutex to lock > + * @ctx: optional w/w acquire context > + * > + * Trylocks a mutex with the optional acquire context; no deadlock detection is > + * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise. > + * > + * Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is > + * specified, -EALREADY and -EDEADLK handling may happen in calls to ww_mutex_lock. > + * > + * A mutex acquired with this function must be released with ww_mutex_unlock. > + */ > +int __sched > +ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ctx) > +{ > + bool locked; > + > + if (!ctx) > + return mutex_trylock(&ww->base); > + > +#ifdef CONFIG_DEBUG_MUTEXES > + DEBUG_LOCKS_WARN_ON(ww->base.magic != &ww->base); > +#endif > + > + preempt_disable(); > + locked = __mutex_trylock(&ww->base); > + > + if (locked) { > + ww_mutex_set_context_fastpath(ww, ctx); > + mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ctx->dep_map, _RET_IP_); > + } > + preempt_enable(); > + > + return locked; > +} > +EXPORT_SYMBOL(ww_mutex_trylock); You'll need a similar hunk in ww_rt_mutex.c