LCOV - code coverage report
Current view: top level - drivers/gpu/drm - drm_modeset_lock.c (source / functions) Hit Total Coverage
Test: coverage.info Lines: 34 102 33.3 %
Date: 2023-03-27 20:00:47 Functions: 6 13 46.2 %

          Line data    Source code
       1             : /*
       2             :  * Copyright (C) 2014 Red Hat
       3             :  * Author: Rob Clark <robdclark@gmail.com>
       4             :  *
       5             :  * Permission is hereby granted, free of charge, to any person obtaining a
       6             :  * copy of this software and associated documentation files (the "Software"),
       7             :  * to deal in the Software without restriction, including without limitation
       8             :  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
       9             :  * and/or sell copies of the Software, and to permit persons to whom the
      10             :  * Software is furnished to do so, subject to the following conditions:
      11             :  *
      12             :  * The above copyright notice and this permission notice shall be included in
      13             :  * all copies or substantial portions of the Software.
      14             :  *
      15             :  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
      16             :  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
      17             :  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
      18             :  * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
      19             :  * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
      20             :  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
      21             :  * OTHER DEALINGS IN THE SOFTWARE.
      22             :  */
      23             : 
      24             : #include <drm/drm_atomic.h>
      25             : #include <drm/drm_crtc.h>
      26             : #include <drm/drm_device.h>
      27             : #include <drm/drm_modeset_lock.h>
      28             : #include <drm/drm_print.h>
      29             : 
      30             : /**
      31             :  * DOC: kms locking
      32             :  *
      33             :  * As KMS moves toward more fine grained locking, and atomic ioctl where
      34             :  * userspace can indirectly control locking order, it becomes necessary
      35             :  * to use &ww_mutex and acquire-contexts to avoid deadlocks.  But because
      36             :  * the locking is more distributed around the driver code, we want a bit
      37             :  * of extra utility/tracking out of our acquire-ctx.  This is provided
      38             :  * by &struct drm_modeset_lock and &struct drm_modeset_acquire_ctx.
      39             :  *
      40             :  * For basic principles of &ww_mutex, see: Documentation/locking/ww-mutex-design.rst
      41             :  *
      42             :  * The basic usage pattern is to::
      43             :  *
      44             :  *     drm_modeset_acquire_init(ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
      45             :  *     retry:
      46             :  *     foreach (lock in random_ordered_set_of_locks) {
      47             :  *         ret = drm_modeset_lock(lock, ctx)
      48             :  *         if (ret == -EDEADLK) {
      49             :  *             ret = drm_modeset_backoff(ctx);
      50             :  *             if (!ret)
      51             :  *                 goto retry;
      52             :  *         }
      53             :  *         if (ret)
      54             :  *             goto out;
      55             :  *     }
      56             :  *     ... do stuff ...
      57             :  *     out:
      58             :  *     drm_modeset_drop_locks(ctx);
      59             :  *     drm_modeset_acquire_fini(ctx);
      60             :  *
      61             :  * For convenience this control flow is implemented in
      62             :  * DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() for the case
      63             :  * where all modeset locks need to be taken through drm_modeset_lock_all_ctx().
      64             :  *
      65             :  * If all that is needed is a single modeset lock, then the &struct
      66             :  * drm_modeset_acquire_ctx is not needed and the locking can be simplified
      67             :  * by passing a NULL instead of ctx in the drm_modeset_lock() call or
      68             :  * calling  drm_modeset_lock_single_interruptible(). To unlock afterwards
      69             :  * call drm_modeset_unlock().
      70             :  *
      71             :  * On top of these per-object locks using &ww_mutex there's also an overall
      72             :  * &drm_mode_config.mutex, for protecting everything else. Mostly this means
      73             :  * probe state of connectors, and preventing hotplug add/removal of connectors.
      74             :  *
      75             :  * Finally there's a bunch of dedicated locks to protect drm core internal
      76             :  * lists and lookup data structures.
      77             :  */
      78             : 
      79             : static DEFINE_WW_CLASS(crtc_ww_class);
      80             : 
      81             : #if IS_ENABLED(CONFIG_DRM_DEBUG_MODESET_LOCK)
      82             : static noinline depot_stack_handle_t __drm_stack_depot_save(void)
      83             : {
      84             :         unsigned long entries[8];
      85             :         unsigned int n;
      86             : 
      87             :         n = stack_trace_save(entries, ARRAY_SIZE(entries), 1);
      88             : 
      89             :         return stack_depot_save(entries, n, GFP_NOWAIT | __GFP_NOWARN);
      90             : }
      91             : 
      92             : static void __drm_stack_depot_print(depot_stack_handle_t stack_depot)
      93             : {
      94             :         struct drm_printer p = drm_debug_printer("drm_modeset_lock");
      95             :         unsigned long *entries;
      96             :         unsigned int nr_entries;
      97             :         char *buf;
      98             : 
      99             :         buf = kmalloc(PAGE_SIZE, GFP_NOWAIT | __GFP_NOWARN);
     100             :         if (!buf)
     101             :                 return;
     102             : 
     103             :         nr_entries = stack_depot_fetch(stack_depot, &entries);
     104             :         stack_trace_snprint(buf, PAGE_SIZE, entries, nr_entries, 2);
     105             : 
     106             :         drm_printf(&p, "attempting to lock a contended lock without backoff:\n%s", buf);
     107             : 
     108             :         kfree(buf);
     109             : }
     110             : 
     111             : static void __drm_stack_depot_init(void)
     112             : {
     113             :         stack_depot_init();
     114             : }
     115             : #else /* CONFIG_DRM_DEBUG_MODESET_LOCK */
     116             : static depot_stack_handle_t __drm_stack_depot_save(void)
     117             : {
     118             :         return 0;
     119             : }
     120             : static void __drm_stack_depot_print(depot_stack_handle_t stack_depot)
     121             : {
     122             : }
     123             : static void __drm_stack_depot_init(void)
     124             : {
     125             : }
     126             : #endif /* CONFIG_DRM_DEBUG_MODESET_LOCK */
     127             : 
     128             : /**
     129             :  * drm_modeset_lock_all - take all modeset locks
     130             :  * @dev: DRM device
     131             :  *
     132             :  * This function takes all modeset locks, suitable where a more fine-grained
     133             :  * scheme isn't (yet) implemented. Locks must be dropped by calling the
     134             :  * drm_modeset_unlock_all() function.
     135             :  *
     136             :  * This function is deprecated. It allocates a lock acquisition context and
     137             :  * stores it in &drm_device.mode_config. This facilitate conversion of
     138             :  * existing code because it removes the need to manually deal with the
     139             :  * acquisition context, but it is also brittle because the context is global
     140             :  * and care must be taken not to nest calls. New code should use the
     141             :  * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
     142             :  */
     143           0 : void drm_modeset_lock_all(struct drm_device *dev)
     144             : {
     145           0 :         struct drm_mode_config *config = &dev->mode_config;
     146             :         struct drm_modeset_acquire_ctx *ctx;
     147             :         int ret;
     148             : 
     149           0 :         ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL);
     150           0 :         if (WARN_ON(!ctx))
     151             :                 return;
     152             : 
     153           0 :         mutex_lock(&config->mutex);
     154             : 
     155           0 :         drm_modeset_acquire_init(ctx, 0);
     156             : 
     157             : retry:
     158           0 :         ret = drm_modeset_lock_all_ctx(dev, ctx);
     159           0 :         if (ret < 0) {
     160           0 :                 if (ret == -EDEADLK) {
     161           0 :                         drm_modeset_backoff(ctx);
     162           0 :                         goto retry;
     163             :                 }
     164             : 
     165           0 :                 drm_modeset_acquire_fini(ctx);
     166           0 :                 kfree(ctx);
     167           0 :                 return;
     168             :         }
     169           0 :         ww_acquire_done(&ctx->ww_ctx);
     170             : 
     171           0 :         WARN_ON(config->acquire_ctx);
     172             : 
     173             :         /*
     174             :          * We hold the locks now, so it is safe to stash the acquisition
     175             :          * context for drm_modeset_unlock_all().
     176             :          */
     177           0 :         config->acquire_ctx = ctx;
     178             : 
     179           0 :         drm_warn_on_modeset_not_all_locked(dev);
     180             : }
     181             : EXPORT_SYMBOL(drm_modeset_lock_all);
     182             : 
     183             : /**
     184             :  * drm_modeset_unlock_all - drop all modeset locks
     185             :  * @dev: DRM device
     186             :  *
     187             :  * This function drops all modeset locks taken by a previous call to the
     188             :  * drm_modeset_lock_all() function.
     189             :  *
     190             :  * This function is deprecated. It uses the lock acquisition context stored
     191             :  * in &drm_device.mode_config. This facilitates conversion of existing
     192             :  * code because it removes the need to manually deal with the acquisition
     193             :  * context, but it is also brittle because the context is global and care must
     194             :  * be taken not to nest calls. New code should pass the acquisition context
     195             :  * directly to the drm_modeset_drop_locks() function.
     196             :  */
     197           0 : void drm_modeset_unlock_all(struct drm_device *dev)
     198             : {
     199           0 :         struct drm_mode_config *config = &dev->mode_config;
     200           0 :         struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
     201             : 
     202           0 :         if (WARN_ON(!ctx))
     203             :                 return;
     204             : 
     205           0 :         config->acquire_ctx = NULL;
     206           0 :         drm_modeset_drop_locks(ctx);
     207           0 :         drm_modeset_acquire_fini(ctx);
     208             : 
     209           0 :         kfree(ctx);
     210             : 
     211           0 :         mutex_unlock(&dev->mode_config.mutex);
     212             : }
     213             : EXPORT_SYMBOL(drm_modeset_unlock_all);
     214             : 
     215             : /**
     216             :  * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
     217             :  * @dev: device
     218             :  *
     219             :  * Useful as a debug assert.
     220             :  */
     221           0 : void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
     222             : {
     223             :         struct drm_crtc *crtc;
     224             : 
     225             :         /* Locking is currently fubar in the panic handler. */
     226           0 :         if (oops_in_progress)
     227             :                 return;
     228             : 
     229           0 :         drm_for_each_crtc(crtc, dev)
     230           0 :                 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
     231             : 
     232           0 :         WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
     233           0 :         WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
     234             : }
     235             : EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
     236             : 
     237             : /**
     238             :  * drm_modeset_acquire_init - initialize acquire context
     239             :  * @ctx: the acquire context
     240             :  * @flags: 0 or %DRM_MODESET_ACQUIRE_INTERRUPTIBLE
     241             :  *
     242             :  * When passing %DRM_MODESET_ACQUIRE_INTERRUPTIBLE to @flags,
     243             :  * all calls to drm_modeset_lock() will perform an interruptible
     244             :  * wait.
     245             :  */
     246           5 : void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
     247             :                 uint32_t flags)
     248             : {
     249           5 :         memset(ctx, 0, sizeof(*ctx));
     250          10 :         ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
     251          10 :         INIT_LIST_HEAD(&ctx->locked);
     252             : 
     253           5 :         if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
     254           0 :                 ctx->interruptible = true;
     255           5 : }
     256             : EXPORT_SYMBOL(drm_modeset_acquire_init);
     257             : 
     258             : /**
     259             :  * drm_modeset_acquire_fini - cleanup acquire context
     260             :  * @ctx: the acquire context
     261             :  */
     262           5 : void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
     263             : {
     264           5 :         ww_acquire_fini(&ctx->ww_ctx);
     265           5 : }
     266             : EXPORT_SYMBOL(drm_modeset_acquire_fini);
     267             : 
     268             : /**
     269             :  * drm_modeset_drop_locks - drop all locks
     270             :  * @ctx: the acquire context
     271             :  *
     272             :  * Drop all locks currently held against this acquire context.
     273             :  */
     274           5 : void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
     275             : {
     276           5 :         if (WARN_ON(ctx->contended))
     277             :                 __drm_stack_depot_print(ctx->stack_depot);
     278             : 
     279          20 :         while (!list_empty(&ctx->locked)) {
     280             :                 struct drm_modeset_lock *lock;
     281             : 
     282           5 :                 lock = list_first_entry(&ctx->locked,
     283             :                                 struct drm_modeset_lock, head);
     284             : 
     285             :                 drm_modeset_unlock(lock);
     286             :         }
     287           5 : }
     288             : EXPORT_SYMBOL(drm_modeset_drop_locks);
     289             : 
     290          10 : static inline int modeset_lock(struct drm_modeset_lock *lock,
     291             :                 struct drm_modeset_acquire_ctx *ctx,
     292             :                 bool interruptible, bool slow)
     293             : {
     294             :         int ret;
     295             : 
     296          10 :         if (WARN_ON(ctx->contended))
     297             :                 __drm_stack_depot_print(ctx->stack_depot);
     298             : 
     299          10 :         if (ctx->trylock_only) {
     300             :                 lockdep_assert_held(&ctx->ww_ctx);
     301             : 
     302           0 :                 if (!ww_mutex_trylock(&lock->mutex, NULL))
     303             :                         return -EBUSY;
     304             :                 else
     305           0 :                         return 0;
     306          10 :         } else if (interruptible && slow) {
     307           0 :                 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
     308          10 :         } else if (interruptible) {
     309           0 :                 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
     310          10 :         } else if (slow) {
     311           0 :                 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
     312           0 :                 ret = 0;
     313             :         } else {
     314          10 :                 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
     315             :         }
     316          10 :         if (!ret) {
     317          10 :                 WARN_ON(!list_empty(&lock->head));
     318           5 :                 list_add(&lock->head, &ctx->locked);
     319           5 :         } else if (ret == -EALREADY) {
     320             :                 /* we already hold the lock.. this is fine.  For atomic
     321             :                  * we will need to be able to drm_modeset_lock() things
     322             :                  * without having to keep track of what is already locked
     323             :                  * or not.
     324             :                  */
     325             :                 ret = 0;
     326           0 :         } else if (ret == -EDEADLK) {
     327           0 :                 ctx->contended = lock;
     328           0 :                 ctx->stack_depot = __drm_stack_depot_save();
     329             :         }
     330             : 
     331             :         return ret;
     332             : }
     333             : 
     334             : /**
     335             :  * drm_modeset_backoff - deadlock avoidance backoff
     336             :  * @ctx: the acquire context
     337             :  *
     338             :  * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
     339             :  * you must call this function to drop all currently held locks and
     340             :  * block until the contended lock becomes available.
     341             :  *
     342             :  * This function returns 0 on success, or -ERESTARTSYS if this context
     343             :  * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the
     344             :  * wait has been interrupted.
     345             :  */
     346           0 : int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
     347             : {
     348           0 :         struct drm_modeset_lock *contended = ctx->contended;
     349             : 
     350           0 :         ctx->contended = NULL;
     351           0 :         ctx->stack_depot = 0;
     352             : 
     353           0 :         if (WARN_ON(!contended))
     354             :                 return 0;
     355             : 
     356           0 :         drm_modeset_drop_locks(ctx);
     357             : 
     358           0 :         return modeset_lock(contended, ctx, ctx->interruptible, true);
     359             : }
     360             : EXPORT_SYMBOL(drm_modeset_backoff);
     361             : 
     362             : /**
     363             :  * drm_modeset_lock_init - initialize lock
     364             :  * @lock: lock to init
     365             :  */
     366          17 : void drm_modeset_lock_init(struct drm_modeset_lock *lock)
     367             : {
     368          34 :         ww_mutex_init(&lock->mutex, &crtc_ww_class);
     369          34 :         INIT_LIST_HEAD(&lock->head);
     370             :         __drm_stack_depot_init();
     371          17 : }
     372             : EXPORT_SYMBOL(drm_modeset_lock_init);
     373             : 
     374             : /**
     375             :  * drm_modeset_lock - take modeset lock
     376             :  * @lock: lock to take
     377             :  * @ctx: acquire ctx
     378             :  *
     379             :  * If @ctx is not NULL, then its ww acquire context is used and the
     380             :  * lock will be tracked by the context and can be released by calling
     381             :  * drm_modeset_drop_locks().  If -EDEADLK is returned, this means a
     382             :  * deadlock scenario has been detected and it is an error to attempt
     383             :  * to take any more locks without first calling drm_modeset_backoff().
     384             :  *
     385             :  * If the @ctx is not NULL and initialized with
     386             :  * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with
     387             :  * -ERESTARTSYS when interrupted.
     388             :  *
     389             :  * If @ctx is NULL then the function call behaves like a normal,
     390             :  * uninterruptible non-nesting mutex_lock() call.
     391             :  */
     392          10 : int drm_modeset_lock(struct drm_modeset_lock *lock,
     393             :                 struct drm_modeset_acquire_ctx *ctx)
     394             : {
     395          10 :         if (ctx)
     396          10 :                 return modeset_lock(lock, ctx, ctx->interruptible, false);
     397             : 
     398           0 :         ww_mutex_lock(&lock->mutex, NULL);
     399           0 :         return 0;
     400             : }
     401             : EXPORT_SYMBOL(drm_modeset_lock);
     402             : 
     403             : /**
     404             :  * drm_modeset_lock_single_interruptible - take a single modeset lock
     405             :  * @lock: lock to take
     406             :  *
     407             :  * This function behaves as drm_modeset_lock() with a NULL context,
     408             :  * but performs interruptible waits.
     409             :  *
     410             :  * This function returns 0 on success, or -ERESTARTSYS when interrupted.
     411             :  */
     412           0 : int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock)
     413             : {
     414           0 :         return ww_mutex_lock_interruptible(&lock->mutex, NULL);
     415             : }
     416             : EXPORT_SYMBOL(drm_modeset_lock_single_interruptible);
     417             : 
     418             : /**
     419             :  * drm_modeset_unlock - drop modeset lock
     420             :  * @lock: lock to release
     421             :  */
     422           0 : void drm_modeset_unlock(struct drm_modeset_lock *lock)
     423             : {
     424          10 :         list_del_init(&lock->head);
     425           5 :         ww_mutex_unlock(&lock->mutex);
     426           0 : }
     427             : EXPORT_SYMBOL(drm_modeset_unlock);
     428             : 
     429             : /**
     430             :  * drm_modeset_lock_all_ctx - take all modeset locks
     431             :  * @dev: DRM device
     432             :  * @ctx: lock acquisition context
     433             :  *
     434             :  * This function takes all modeset locks, suitable where a more fine-grained
     435             :  * scheme isn't (yet) implemented.
     436             :  *
     437             :  * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex
     438             :  * since that lock isn't required for modeset state changes. Callers which
     439             :  * need to grab that lock too need to do so outside of the acquire context
     440             :  * @ctx.
     441             :  *
     442             :  * Locks acquired with this function should be released by calling the
     443             :  * drm_modeset_drop_locks() function on @ctx.
     444             :  *
     445             :  * See also: DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END()
     446             :  *
     447             :  * Returns: 0 on success or a negative error-code on failure.
     448             :  */
     449           0 : int drm_modeset_lock_all_ctx(struct drm_device *dev,
     450             :                              struct drm_modeset_acquire_ctx *ctx)
     451             : {
     452             :         struct drm_private_obj *privobj;
     453             :         struct drm_crtc *crtc;
     454             :         struct drm_plane *plane;
     455             :         int ret;
     456             : 
     457           0 :         ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
     458           0 :         if (ret)
     459             :                 return ret;
     460             : 
     461           0 :         drm_for_each_crtc(crtc, dev) {
     462           0 :                 ret = drm_modeset_lock(&crtc->mutex, ctx);
     463           0 :                 if (ret)
     464             :                         return ret;
     465             :         }
     466             : 
     467           0 :         drm_for_each_plane(plane, dev) {
     468           0 :                 ret = drm_modeset_lock(&plane->mutex, ctx);
     469           0 :                 if (ret)
     470             :                         return ret;
     471             :         }
     472             : 
     473           0 :         drm_for_each_privobj(privobj, dev) {
     474           0 :                 ret = drm_modeset_lock(&privobj->lock, ctx);
     475           0 :                 if (ret)
     476             :                         return ret;
     477             :         }
     478             : 
     479             :         return 0;
     480             : }
     481             : EXPORT_SYMBOL(drm_modeset_lock_all_ctx);

Generated by: LCOV version 1.14