| Message ID | 20210917123513.1106-17-christian.koenig@amd.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [01/26] dma-buf: add dma_resv_for_each_fence_unlocked v2 | expand |
On 17/09/2021 13:35, Christian König wrote: > Simplifying the code a bit. > > v2: add missing rcu read unlock. > > Signed-off-by: Christian König <christian.koenig@amd.com> > --- > drivers/gpu/drm/i915/gem/i915_gem_wait.c | 57 ++++++------------------ > 1 file changed, 14 insertions(+), 43 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_wait.c b/drivers/gpu/drm/i915/gem/i915_gem_wait.c > index f909aaa09d9c..e416cf528635 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_wait.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_wait.c > @@ -37,55 +37,26 @@ i915_gem_object_wait_reservation(struct dma_resv *resv, > unsigned int flags, > long timeout) > { > - struct dma_fence *excl; > - bool prune_fences = false; > - > - if (flags & I915_WAIT_ALL) { > - struct dma_fence **shared; > - unsigned int count, i; > - int ret; > - > - ret = dma_resv_get_fences(resv, &excl, &count, &shared); > - if (ret) > - return ret; > - > - for (i = 0; i < count; i++) { > - timeout = i915_gem_object_wait_fence(shared[i], > - flags, timeout); > - if (timeout < 0) > - break; > - > - dma_fence_put(shared[i]); > - } > - > - for (; i < count; i++) > - dma_fence_put(shared[i]); > - kfree(shared); > - > - /* > - * If both shared fences and an exclusive fence exist, > - * then by construction the shared fences must be later > - * than the exclusive fence. If we successfully wait for > - * all the shared fences, we know that the exclusive fence > - * must all be signaled. If all the shared fences are > - * signaled, we can prune the array and recover the > - * floating references on the fences/requests. > - */ > - prune_fences = count && timeout >= 0; > - } else { > - excl = dma_resv_get_excl_unlocked(resv); > + struct dma_resv_iter cursor; > + struct dma_fence *fence; > + > + rcu_read_lock(); > + dma_resv_iter_begin(&cursor, resv, flags & I915_WAIT_ALL); > + dma_resv_for_each_fence_unlocked(&cursor, fence) { > + rcu_read_unlock(); > + timeout = i915_gem_object_wait_fence(fence, flags, timeout); Converting this one could be problematic. It's the wait ioctl which used to grab an atomic snapshot and wait for that rendering to complete. With this change I think it has the potential to run forever keeps catching new activity against the same object. I am not sure whether or not the difference is relevant for how userspace uses it but I think needs discussion. Hm actually there are internal callers as well, and at least some of those have the object locked. Would a wider refactoring to separate those into buckets (locked vs unlocked) make sense? Regards, Tvrtko > + rcu_read_lock(); > + if (timeout < 0) > + break; > } > - > - if (excl && timeout >= 0) > - timeout = i915_gem_object_wait_fence(excl, flags, timeout); > - > - dma_fence_put(excl); > + dma_resv_iter_end(&cursor); > + rcu_read_unlock(); > > /* > * Opportunistically prune the fences iff we know they have *all* been > * signaled. > */ > - if (prune_fences) > + if (timeout > 0) > dma_resv_prune(resv); > > return timeout; >
Am 20.09.21 um 12:00 schrieb Tvrtko Ursulin: > > On 17/09/2021 13:35, Christian König wrote: >> Simplifying the code a bit. >> >> v2: add missing rcu read unlock. >> >> Signed-off-by: Christian König <christian.koenig@amd.com> >> --- >> drivers/gpu/drm/i915/gem/i915_gem_wait.c | 57 ++++++------------------ >> 1 file changed, 14 insertions(+), 43 deletions(-) >> >> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_wait.c >> b/drivers/gpu/drm/i915/gem/i915_gem_wait.c >> index f909aaa09d9c..e416cf528635 100644 >> --- a/drivers/gpu/drm/i915/gem/i915_gem_wait.c >> +++ b/drivers/gpu/drm/i915/gem/i915_gem_wait.c >> @@ -37,55 +37,26 @@ i915_gem_object_wait_reservation(struct dma_resv >> *resv, >> unsigned int flags, >> long timeout) >> { >> - struct dma_fence *excl; >> - bool prune_fences = false; >> - >> - if (flags & I915_WAIT_ALL) { >> - struct dma_fence **shared; >> - unsigned int count, i; >> - int ret; >> - >> - ret = dma_resv_get_fences(resv, &excl, &count, &shared); >> - if (ret) >> - return ret; >> - >> - for (i = 0; i < count; i++) { >> - timeout = i915_gem_object_wait_fence(shared[i], >> - flags, timeout); >> - if (timeout < 0) >> - break; >> - >> - dma_fence_put(shared[i]); >> - } >> - >> - for (; i < count; i++) >> - dma_fence_put(shared[i]); >> - kfree(shared); >> - >> - /* >> - * If both shared fences and an exclusive fence exist, >> - * then by construction the shared fences must be later >> - * than the exclusive fence. If we successfully wait for >> - * all the shared fences, we know that the exclusive fence >> - * must all be signaled. If all the shared fences are >> - * signaled, we can prune the array and recover the >> - * floating references on the fences/requests. >> - */ >> - prune_fences = count && timeout >= 0; >> - } else { >> - excl = dma_resv_get_excl_unlocked(resv); >> + struct dma_resv_iter cursor; >> + struct dma_fence *fence; >> + >> + rcu_read_lock(); >> + dma_resv_iter_begin(&cursor, resv, flags & I915_WAIT_ALL); >> + dma_resv_for_each_fence_unlocked(&cursor, fence) { >> + rcu_read_unlock(); >> + timeout = i915_gem_object_wait_fence(fence, flags, timeout); > > Converting this one could be problematic. It's the wait ioctl which > used to grab an atomic snapshot and wait for that rendering to > complete. With this change I think it has the potential to run forever > keeps catching new activity against the same object. > > I am not sure whether or not the difference is relevant for how > userspace uses it but I think needs discussion. It was years ago, but IIRC we had the same discussion for the dma_resv_wait_timeout() function and the result was that this is not a valid use case and waiting forever if you see new work over and over again is a valid result. Let me double check the history of this code here as well. > Hm actually there are internal callers as well, and at least some of > those have the object locked. Would a wider refactoring to separate > those into buckets (locked vs unlocked) make sense? Yes definitely. Regards, Christian. > > Regards, > > Tvrtko > > >> + rcu_read_lock(); >> + if (timeout < 0) >> + break; >> } >> - >> - if (excl && timeout >= 0) >> - timeout = i915_gem_object_wait_fence(excl, flags, timeout); >> - >> - dma_fence_put(excl); >> + dma_resv_iter_end(&cursor); >> + rcu_read_unlock(); >> /* >> * Opportunistically prune the fences iff we know they have >> *all* been >> * signaled. >> */ >> - if (prune_fences) >> + if (timeout > 0) >> dma_resv_prune(resv); >> return timeout; >>
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_wait.c b/drivers/gpu/drm/i915/gem/i915_gem_wait.c index f909aaa09d9c..e416cf528635 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_wait.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_wait.c @@ -37,55 +37,26 @@ i915_gem_object_wait_reservation(struct dma_resv *resv, unsigned int flags, long timeout) { - struct dma_fence *excl; - bool prune_fences = false; - - if (flags & I915_WAIT_ALL) { - struct dma_fence **shared; - unsigned int count, i; - int ret; - - ret = dma_resv_get_fences(resv, &excl, &count, &shared); - if (ret) - return ret; - - for (i = 0; i < count; i++) { - timeout = i915_gem_object_wait_fence(shared[i], - flags, timeout); - if (timeout < 0) - break; - - dma_fence_put(shared[i]); - } - - for (; i < count; i++) - dma_fence_put(shared[i]); - kfree(shared); - - /* - * If both shared fences and an exclusive fence exist, - * then by construction the shared fences must be later - * than the exclusive fence. If we successfully wait for - * all the shared fences, we know that the exclusive fence - * must all be signaled. If all the shared fences are - * signaled, we can prune the array and recover the - * floating references on the fences/requests. - */ - prune_fences = count && timeout >= 0; - } else { - excl = dma_resv_get_excl_unlocked(resv); + struct dma_resv_iter cursor; + struct dma_fence *fence; + + rcu_read_lock(); + dma_resv_iter_begin(&cursor, resv, flags & I915_WAIT_ALL); + dma_resv_for_each_fence_unlocked(&cursor, fence) { + rcu_read_unlock(); + timeout = i915_gem_object_wait_fence(fence, flags, timeout); + rcu_read_lock(); + if (timeout < 0) + break; } - - if (excl && timeout >= 0) - timeout = i915_gem_object_wait_fence(excl, flags, timeout); - - dma_fence_put(excl); + dma_resv_iter_end(&cursor); + rcu_read_unlock(); /* * Opportunistically prune the fences iff we know they have *all* been * signaled. */ - if (prune_fences) + if (timeout > 0) dma_resv_prune(resv); return timeout;
Simplifying the code a bit. v2: add missing rcu read unlock. Signed-off-by: Christian König <christian.koenig@amd.com> --- drivers/gpu/drm/i915/gem/i915_gem_wait.c | 57 ++++++------------------ 1 file changed, 14 insertions(+), 43 deletions(-)