On Tue, 13 Feb 2024, Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx> wrote: > Once a user opens an fd for a perf event, if the driver undergoes a > function level reset (FLR), the resources are not cleaned up as > expected. For this discussion FLR is defined as a PCI unbind followed by > a bind. perf_pmu_unregister() would cleanup everything, but when the user > closes the perf fd, perf_release is executed and we encounter null > pointer dereferences and/or list corruption in that path which require a > reboot to recover. > > The only approach that worked to resolve this was to close the file > associated with the event such that the relevant cleanup happens w.r.t. > the open file. To do so, use the event->owner task and find the file > relevant to the event and close it. This relies on the > file->private_data matching the event object. > > Note: > - Closing the event file is a delayed work that gets queued to system_wq. > The close is seen to happen when kernel returns to user space following > the unbind. > > - perf framework will access the pmu object after the last event has > been destroyed. The drm device is refcounted in the init and destroy > hooks, so this causes a use after free if we are releasing the drm > device reference after unbind has been called. To work around this, we > take an extra reference in the unbind path and release it using a > delayed work in the destroy patch. The delayed work is queued to > system_wq. > > Ref: https://lore.kernel.org/lkml/20240115170120.662220-1-tvrtko.ursulin@xxxxxxxxxxxxxxx/T/#me72abfa2771e6fc94b167ce47efdbf391cc313ab > > Opens: > - Synchronization may be needed between i915_pmu_unregister and > i915_pmu_event_destroy to avoid any races. > > - If unbind and bind happen from the same process the event fd is closed > after bind completes. This means that the cleanup would not happen > until bind completes. In this case, i915 loads fine, but pmu > registration fails with an error that the sysfs entries are already > present. There is no solution feasible here. Since this is not a fatal > error (reloading i915 works fine) and the usual case is to have bind and > unbind in separate processes, there is no intention to solve this. > > Other solutions/aspects tried: > - Call perf_event_disable() followed by perf_event_release_kernel() in > the unbind path to clean up the events. This still causes issues when > user closes the fd since perf_event_release_kernel() is called again and > fails requiring reboot. > > - Close all event fds in unbind and wait for the close to complete by > checking if list is empty. This wait does not work since the files > are actually closed when unbind returns to user space. > > Testing: > - New IGT tests have been added for this and are run with KASAN and > kmemleak enabled. > > Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx> > --- > drivers/gpu/drm/i915/i915_pmu.c | 96 ++++++++++++++++++++++++++++++++- > drivers/gpu/drm/i915/i915_pmu.h | 15 ++++++ > 2 files changed, 110 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c > index 4d2a289f848a..2f365c7f5db7 100644 > --- a/drivers/gpu/drm/i915/i915_pmu.c > +++ b/drivers/gpu/drm/i915/i915_pmu.c > @@ -4,6 +4,8 @@ > * Copyright © 2017-2018 Intel Corporation > */ > > +#include <linux/fdtable.h> > +#include <linux/fs.h> > #include <linux/pm_runtime.h> > > #include "gt/intel_engine.h" > @@ -573,9 +575,21 @@ static void i915_pmu_event_destroy(struct perf_event *event) > { > struct i915_pmu *pmu = event_to_pmu(event); > struct drm_i915_private *i915 = pmu_to_i915(pmu); > + struct i915_event *e = event->pmu_private; > > drm_WARN_ON(&i915->drm, event->parent); > > + if (e) { > + event->pmu_private = NULL; > + list_del(&e->link); > + kfree(e); > + } > + > + if (i915->pmu.closed && list_empty(&i915->pmu.initialized_events)) { > + pmu_teardown(&i915->pmu); > + mod_delayed_work(system_wq, &i915->pmu.work, 50); > + } > + > drm_dev_put(&i915->drm); > } > > @@ -684,6 +698,14 @@ static int i915_pmu_event_init(struct perf_event *event) > return ret; > > if (!event->parent) { > + struct i915_event *e = kzalloc(sizeof(*e), GFP_KERNEL); > + > + if (!e) > + return -ENOMEM; > + > + e->event = event; > + list_add(&e->link, &pmu->initialized_events); > + event->pmu_private = e; > drm_dev_get(&i915->drm); > event->destroy = i915_pmu_event_destroy; > } > @@ -1256,6 +1278,14 @@ void i915_pmu_exit(void) > cpuhp_remove_multi_state(cpuhp_slot); > } > > +static void i915_pmu_release(struct work_struct *work) > +{ > + struct i915_pmu *pmu = container_of(work, typeof(*pmu), work.work); > + struct drm_i915_private *i915 = container_of(pmu, typeof(*i915), pmu); > + > + drm_dev_put(&i915->drm); > +} > + > void i915_pmu_register(struct drm_i915_private *i915) > { > struct i915_pmu *pmu = &i915->pmu; > @@ -1313,6 +1343,9 @@ void i915_pmu_register(struct drm_i915_private *i915) > pmu->base.read = i915_pmu_event_read; > pmu->base.event_idx = i915_pmu_event_event_idx; > > + INIT_LIST_HEAD(&pmu->initialized_events); > + INIT_DELAYED_WORK(&pmu->work, i915_pmu_release); > + > ret = perf_pmu_register(&pmu->base, pmu->name, -1); > if (ret) > goto err_groups; > @@ -1337,6 +1370,64 @@ void i915_pmu_register(struct drm_i915_private *i915) > drm_notice(&i915->drm, "Failed to register PMU!\n"); > } > > +/* Ref: close_fd() */ > +static unsigned int __open_files(struct fdtable *fdt) > +{ > + unsigned int size = fdt->max_fds; > + unsigned int i; > + > + for (i = size / BITS_PER_LONG; i > 0; ) { > + if (fdt->open_fds[--i]) > + break; > + } > + return (i + 1) * BITS_PER_LONG; > +} > + > +static void close_event_file(struct perf_event *event) > +{ > + unsigned int max_open_fds, fd; > + struct files_struct *files; > + struct task_struct *task; > + struct fdtable *fdt; > + > + task = event->owner; > + if (!task) > + return; > + > + files = task->files; > + if (!files) > + return; > + > + spin_lock(&files->file_lock); > + fdt = files_fdtable(files); > + max_open_fds = __open_files(fdt); > + for (fd = 0; fd < max_open_fds; fd++) { > + struct file *file = fdt->fd[fd]; > + > + if (!file || file->private_data != event) > + continue; > + > + rcu_assign_pointer(fdt->fd[fd], NULL); > + __clear_bit(fd, fdt->open_fds); > + __clear_bit(fd / BITS_PER_LONG, fdt->full_fds_bits); > + if (fd < files->next_fd) > + files->next_fd = fd; > + filp_close(file, files); > + break; > + } > + spin_unlock(&files->file_lock); > +} > + > +static void cleanup_events(struct i915_pmu *pmu) > +{ > + struct drm_i915_private *i915 = container_of(pmu, typeof(*i915), pmu); > + struct i915_event *e, *tmp; > + > + drm_dev_get(&i915->drm); > + list_for_each_entry_safe(e, tmp, &pmu->initialized_events, link) > + close_event_file(e->event); > +} > + > void i915_pmu_unregister(struct drm_i915_private *i915) > { > struct i915_pmu *pmu = &i915->pmu; > @@ -1354,5 +1445,8 @@ void i915_pmu_unregister(struct drm_i915_private *i915) > > hrtimer_cancel(&pmu->timer); > > - pmu_teardown(pmu); > + if (list_empty(&pmu->initialized_events)) > + pmu_teardown(pmu); > + else > + cleanup_events(pmu); > } > diff --git a/drivers/gpu/drm/i915/i915_pmu.h b/drivers/gpu/drm/i915/i915_pmu.h > index 41af038c3738..6f62e820f34d 100644 > --- a/drivers/gpu/drm/i915/i915_pmu.h > +++ b/drivers/gpu/drm/i915/i915_pmu.h > @@ -55,6 +55,11 @@ struct i915_pmu_sample { > u64 cur; > }; > > +struct i915_event { > + struct perf_event *event; > + struct list_head link; > +}; > + Nobody needs this outside of i915_pmu.c. > struct i915_pmu { > /** > * @cpuhp: Struct used for CPU hotplug handling. > @@ -152,6 +157,16 @@ struct i915_pmu { > * @pmu_attr: Memory block holding device attributes. > */ > void *pmu_attr; > + > + /** > + * @initialized_events: List of initialized events > + */ > + struct list_head initialized_events; > + > + /** > + * @work: worker to delay release of drm device reference > + */ > + struct delayed_work work; > }; > > #ifdef CONFIG_PERF_EVENTS -- Jani Nikula, Intel
