[Intel-gfx] [PATCH 3/6] drm/i915: Use a table for i915_init/exit
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Wed Jul 21 09:06:06 UTC 2021
On 20/07/2021 19:13, Jason Ekstrand wrote:
> If the driver was not fully loaded, we may still have globals lying
> around. If we don't tear those down in i915_exit(), we'll leak a bunch
> of memory slabs. This can happen two ways: use_kms = false and if we've
> run mock selftests. In either case, we have an early exit from
> i915_init which happens after i915_globals_init() and we need to clean
> up those globals.
>
> The mock selftests case is especially sticky. The load isn't entirely
> a no-op. We actually do quite a bit inside those selftests including
> allocating a bunch of mock objects and running tests on them. Once all
> those tests are complete, we exit early from i915_init(). Perviously,
> i915_init() would return a non-zero error code on failure and a zero
> error code on success. In the success case, we would get to i915_exit()
> and check i915_pci_driver.driver.owner to detect if i915_init exited early
> and do nothing. In the failure case, we would fail i915_init() but
> there would be no opportunity to clean up globals.
>
> The most annoying part is that you don't actually notice the failure as
> part of the self-tests since leaking a bit of memory, while bad, doesn't
> result in anything observable from userspace. Instead, the next time we
> load the driver (usually for next IGT test), i915_globals_init() gets
> invoked again, we go to allocate a bunch of new memory slabs, those
> implicitly create debugfs entries, and debugfs warns that we're trying
> to create directories and files that already exist. Since this all
> happens as part of the next driver load, it shows up in the dmesg-warn
> of whatever IGT test ran after the mock selftests.
>
> While the obvious thing to do here might be to call i915_globals_exit()
> after selftests, that's not actually safe. The dma-buf selftests call
> i915_gem_prime_export which creates a file. We call dma_buf_put() on
> the resulting dmabuf which calls fput() on the file. However, fput()
> isn't immediate and gets flushed right before syscall returns. This
> means that all the fput()s from the selftests don't happen until right
> before the module load syscall used to fire off the selftests returns
> which is after i915_init(). If we call i915_globals_exit() in
> i915_init() after selftests, we end up freeing slabs out from under
> objects which won't get released until fput() is flushed at the end of
> the module load syscall.
>
> The solution here is to let i915_init() return success early and detect
> the early success in i915_exit() and only tear down globals and nothing
> else. This way the module loads successfully, regardless of the success
> or failure of the tests. Because we've not enumerated any PCI devices,
> no device nodes are created and it's entirely useless from userspace.
> The only thing the module does at that point is hold on to a bit of
> memory until we unload it and i915_exit() is called. Importantly, this
> means that everything from our selftests has the ability to properly
> flush out between i915_init() and i915_exit() because there is at least
> one syscall boundary in between.
>
> In order to handle all the delicate init/exit cases, we convert the
> whole thing to a table of init/exit pairs and track the init status in
> the new init_progress global. This allows us to ensure that i915_exit()
> always tears down exactly the things that i915_init() successfully
> initialized. We also allow early-exit of i915_init() without failure by
> an init function returning > 0. This is useful for nomodeset, and
> selftests. For the mock selftests, we convert them to always return 1
> so we get the desired behavior of the driver always succeeding to load
> the driver and then properly tearing down the partially loaded driver.
>
> Signed-off-by: Jason Ekstrand <jason at jlekstrand.net>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
> drivers/gpu/drm/i915/i915_pci.c | 104 ++++++++++++------
> drivers/gpu/drm/i915/i915_perf.c | 3 +-
> drivers/gpu/drm/i915/i915_perf.h | 2 +-
> drivers/gpu/drm/i915/i915_pmu.c | 4 +-
> drivers/gpu/drm/i915/i915_pmu.h | 4 +-
> .../gpu/drm/i915/selftests/i915_selftest.c | 2 +-
> 6 files changed, 80 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_pci.c b/drivers/gpu/drm/i915/i915_pci.c
> index 4e627b57d31a2..64ebd89eae6ce 100644
> --- a/drivers/gpu/drm/i915/i915_pci.c
> +++ b/drivers/gpu/drm/i915/i915_pci.c
> @@ -1185,27 +1185,9 @@ static void i915_pci_shutdown(struct pci_dev *pdev)
> i915_driver_shutdown(i915);
> }
>
> -static struct pci_driver i915_pci_driver = {
> - .name = DRIVER_NAME,
> - .id_table = pciidlist,
> - .probe = i915_pci_probe,
> - .remove = i915_pci_remove,
> - .shutdown = i915_pci_shutdown,
> - .driver.pm = &i915_pm_ops,
> -};
> -
> -static int __init i915_init(void)
> +static int i915_check_nomodeset(void)
> {
> bool use_kms = true;
> - int err;
> -
> - err = i915_globals_init();
> - if (err)
> - return err;
> -
> - err = i915_mock_selftests();
> - if (err)
> - return err > 0 ? 0 : err;
>
> /*
> * Enable KMS by default, unless explicitly overriden by
> @@ -1222,31 +1204,87 @@ static int __init i915_init(void)
> if (!use_kms) {
> /* Silently fail loading to not upset userspace. */
> DRM_DEBUG_DRIVER("KMS disabled.\n");
> - return 0;
> + return 1;
> }
>
> - i915_pmu_init();
> + return 0;
> +}
>
> - err = pci_register_driver(&i915_pci_driver);
> - if (err) {
> - i915_pmu_exit();
> - i915_globals_exit();
> - return err;
> +static struct pci_driver i915_pci_driver = {
> + .name = DRIVER_NAME,
> + .id_table = pciidlist,
> + .probe = i915_pci_probe,
> + .remove = i915_pci_remove,
> + .shutdown = i915_pci_shutdown,
> + .driver.pm = &i915_pm_ops,
> +};
> +
> +static int i915_register_pci_driver(void)
> +{
> + return pci_register_driver(&i915_pci_driver);
> +}
> +
> +static void i915_unregister_pci_driver(void)
> +{
> + pci_unregister_driver(&i915_pci_driver);
> +}
> +
> +static const struct {
> + int (*init)(void);
> + void (*exit)(void);
> +} init_funcs[] = {
> + { i915_globals_init, i915_globals_exit },
> + { i915_mock_selftests, NULL },
> + { i915_check_nomodeset, NULL },
> + { i915_pmu_init, i915_pmu_exit },
> + { i915_register_pci_driver, i915_unregister_pci_driver },
> + { i915_perf_sysctl_register, i915_perf_sysctl_unregister },
> +};
> +static int init_progress;
> +
> +static int __init i915_init(void)
> +{
> + int err, i;
> +
> + for (i = 0; i < ARRAY_SIZE(init_funcs); i++) {
> + err = init_funcs[i].init();
> + if (err < 0) {
> + while (i--) {
> + if (init_funcs[i].exit)
> + init_funcs[i].exit();
> + }
> + return err;
> + } else if (err > 0) {
> + /*
> + * Early-exit success is reserved for things which
> + * don't have an exit() function because we have no
> + * idea how far they got or how to partially tear
> + * them down.
> + */
> + WARN_ON(init_funcs[i].exit);
I'm not completely happy with the subtlety of where the knowledge of who
needs the module to remain loaded and why ends up. It's partly in the
change of return code from i915_mock_selftests and partly here. But I
don't have any better ideas, which wouldn't have downsides of their own,
on how to express this cleanly so just passing grumbling.
I mean ideally it should be only that specific dma buf test case which
sends out a specific return value requesting not to unload, when it
knows it has used fput. But that would need the i915 selftests runner to
accept the positive error and no idea if that would have some other
consequences without going very deep.
> +
> + /*
> + * We don't want to advertise devices with an only
> + * partially initialized driver.
> + */
> + WARN_ON(i915_pci_driver.driver.owner);
> + break;
> + }
> }
>
> - i915_perf_sysctl_register();
> + init_progress = i;
> +
> return 0;
> }
>
> static void __exit i915_exit(void)
> {
> - if (!i915_pci_driver.driver.owner)
> - return;
> + int i;
>
> - i915_perf_sysctl_unregister();
> - pci_unregister_driver(&i915_pci_driver);
> - i915_pmu_exit();
> - i915_globals_exit();
> + for (i = init_progress - 1; i >= 0; i--) {
Perhaps GEM_BUG_ON(i >= ARRAY_SIZE(init_funcs)) here just in case?
> + if (init_funcs[i].exit)
> + init_funcs[i].exit();
> + }
> }
>
> module_init(i915_init);
> diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
> index b4ec114a4698b..48ddb363b3bda 100644
> --- a/drivers/gpu/drm/i915/i915_perf.c
> +++ b/drivers/gpu/drm/i915/i915_perf.c
> @@ -4483,9 +4483,10 @@ static int destroy_config(int id, void *p, void *data)
> return 0;
> }
>
> -void i915_perf_sysctl_register(void)
> +int i915_perf_sysctl_register(void)
> {
> sysctl_header = register_sysctl_table(dev_root);
> + return 0;
> }
>
> void i915_perf_sysctl_unregister(void)
> diff --git a/drivers/gpu/drm/i915/i915_perf.h b/drivers/gpu/drm/i915/i915_perf.h
> index 882fdd0a76800..1d1329e5af3ae 100644
> --- a/drivers/gpu/drm/i915/i915_perf.h
> +++ b/drivers/gpu/drm/i915/i915_perf.h
> @@ -23,7 +23,7 @@ void i915_perf_fini(struct drm_i915_private *i915);
> void i915_perf_register(struct drm_i915_private *i915);
> void i915_perf_unregister(struct drm_i915_private *i915);
> int i915_perf_ioctl_version(void);
> -void i915_perf_sysctl_register(void);
> +int i915_perf_sysctl_register(void);
> void i915_perf_sysctl_unregister(void);
>
> int i915_perf_open_ioctl(struct drm_device *dev, void *data,
> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
> index 34d37d46a1262..eca92076f31d2 100644
> --- a/drivers/gpu/drm/i915/i915_pmu.c
> +++ b/drivers/gpu/drm/i915/i915_pmu.c
> @@ -1088,7 +1088,7 @@ static int i915_pmu_cpu_offline(unsigned int cpu, struct hlist_node *node)
>
> static enum cpuhp_state cpuhp_slot = CPUHP_INVALID;
>
> -void i915_pmu_init(void)
> +int i915_pmu_init(void)
> {
> int ret;
>
> @@ -1101,6 +1101,8 @@ void i915_pmu_init(void)
> ret);
> else
> cpuhp_slot = ret;
> +
> + return 0;
> }
>
> void i915_pmu_exit(void)
> diff --git a/drivers/gpu/drm/i915/i915_pmu.h b/drivers/gpu/drm/i915/i915_pmu.h
> index 60f9595f902cd..449057648f39b 100644
> --- a/drivers/gpu/drm/i915/i915_pmu.h
> +++ b/drivers/gpu/drm/i915/i915_pmu.h
> @@ -147,14 +147,14 @@ struct i915_pmu {
> };
>
> #ifdef CONFIG_PERF_EVENTS
> -void i915_pmu_init(void);
> +int i915_pmu_init(void);
> void i915_pmu_exit(void);
> void i915_pmu_register(struct drm_i915_private *i915);
> void i915_pmu_unregister(struct drm_i915_private *i915);
> void i915_pmu_gt_parked(struct drm_i915_private *i915);
> void i915_pmu_gt_unparked(struct drm_i915_private *i915);
> #else
> -static inline void i915_pmu_init(void) {}
> +static inline int i915_pmu_init(void) { return 0; }
> static inline void i915_pmu_exit(void) {}
> static inline void i915_pmu_register(struct drm_i915_private *i915) {}
> static inline void i915_pmu_unregister(struct drm_i915_private *i915) {}
> diff --git a/drivers/gpu/drm/i915/selftests/i915_selftest.c b/drivers/gpu/drm/i915/selftests/i915_selftest.c
> index 1bc11c09faef5..935d065725345 100644
> --- a/drivers/gpu/drm/i915/selftests/i915_selftest.c
> +++ b/drivers/gpu/drm/i915/selftests/i915_selftest.c
> @@ -187,7 +187,7 @@ int i915_mock_selftests(void)
> err = run_selftests(mock, NULL);
> if (err) {
> i915_selftest.mock = err;
> - return err;
> + return 1;
I checked igt_kselftest_execute and it looks like it will handle this
change in behaviour so that's fine.
> }
>
> if (i915_selftest.mock < 0) {
>
Regards,
Tvrtko
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