From mboxrd@z Thu Jan 1 00:00:00 1970 From: Akhil P Oommen Subject: Re: [PATCH v2] dma-buf/fence: Take refcount on the module that owns the fence Date: Fri, 22 Jun 2018 17:12:05 +0530 Message-ID: References: <1529660407-6266-1-git-send-email-akhilpo@codeaurora.org> <1529661856.7034.404.camel@padovan.org> <152966212844.11773.6596589902326100250@mail.alporthouse.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <152966212844.11773.6596589902326100250@mail.alporthouse.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Chris Wilson , Gustavo Padovan , sumit.semwal@linaro.org, jcrouse@codeaurora.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org Cc: linux-arm-msm@vger.kernel.org, smasetty@codeaurora.org List-Id: linux-arm-msm@vger.kernel.org On 6/22/2018 3:38 PM, Chris Wilson wrote: > Quoting Gustavo Padovan (2018-06-22 11:04:16) >> Hi Akhil, >> >> On Fri, 2018-06-22 at 15:10 +0530, Akhil P Oommen wrote: >>> Each fence object holds function pointers of the module that >>> initialized >>> it. Allowing the module to unload before this fence's release is >>> catastrophic. So, keep a refcount on the module until the fence is >>> released. >>> >>> Signed-off-by: Akhil P Oommen >>> --- >>> Changes in v2: >>> - added description for the new function parameter. >>> >>> drivers/dma-buf/dma-fence.c | 16 +++++++++++++--- >>> include/linux/dma-fence.h | 10 ++++++++-- >>> 2 files changed, 21 insertions(+), 5 deletions(-) >>> >>> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma- >>> fence.c >>> index 4edb9fd..2aaa44e 100644 >>> --- a/drivers/dma-buf/dma-fence.c >>> +++ b/drivers/dma-buf/dma-fence.c >>> @@ -18,6 +18,7 @@ >>> * more details. >>> */ >>> >>> +#include >>> #include >>> #include >>> #include >>> @@ -168,6 +169,7 @@ void dma_fence_release(struct kref *kref) >>> { >>> struct dma_fence *fence = >>> container_of(kref, struct dma_fence, refcount); >>> + struct module *module = fence->owner; >>> >>> trace_dma_fence_destroy(fence); >>> >>> @@ -178,6 +180,8 @@ void dma_fence_release(struct kref *kref) >>> fence->ops->release(fence); >>> else >>> dma_fence_free(fence); >>> + >>> + module_put(module); >>> } >>> EXPORT_SYMBOL(dma_fence_release); >>> >>> @@ -541,6 +545,7 @@ struct default_wait_cb { >>> >>> /** >>> * dma_fence_init - Initialize a custom fence. >>> + * @module: [in] the module that calls this API >>> * @fence: [in] the fence to initialize >>> * @ops: [in] the dma_fence_ops for operations on this >>> fence >>> * @lock: [in] the irqsafe spinlock to use for locking >>> this fence >>> @@ -556,8 +561,9 @@ struct default_wait_cb { >>> * to check which fence is later by simply using dma_fence_later. >>> */ >>> void >>> -dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops >>> *ops, >>> - spinlock_t *lock, u64 context, unsigned seqno) >>> +_dma_fence_init(struct module *module, struct dma_fence *fence, >>> + const struct dma_fence_ops *ops, spinlock_t *lock, >>> + u64 context, unsigned seqno) >>> { >>> BUG_ON(!lock); >>> BUG_ON(!ops || !ops->wait || !ops->enable_signaling || >>> @@ -571,7 +577,11 @@ struct default_wait_cb { >>> fence->seqno = seqno; >>> fence->flags = 0UL; >>> fence->error = 0; >>> + fence->owner = module; >>> + >>> + if (!try_module_get(module)) >>> + fence->owner = NULL; >>> >>> trace_dma_fence_init(fence); >>> } >>> -EXPORT_SYMBOL(dma_fence_init); >>> +EXPORT_SYMBOL(_dma_fence_init); >> Do we still need to export the symbol, it won't be called from outside >> anymore? Other than that looks good to me: Yes. Because dma_fence_init() is now a macro that resolves to _dma_fence_init(). > There's a big drawback in that a module reference is often insufficient, > and that a reference on the driver (or whatever is required for the > lifetime of the fence) will already hold the module reference. I didn't quite understand what you meant here. Could you please elaborate? > > Considering that we want a few 100k fences in flight per second, is > there no other way to only export a fence with a module reference? > -Chris Thanks, Akhil.