From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 205F3C43219 for ; Fri, 7 Jan 2022 18:18:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348813AbiAGSSc (ORCPT ); Fri, 7 Jan 2022 13:18:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39922 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348807AbiAGSSQ (ORCPT ); Fri, 7 Jan 2022 13:18:16 -0500 Received: from mail-yb1-xb2b.google.com (mail-yb1-xb2b.google.com [IPv6:2607:f8b0:4864:20::b2b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2B70AC06173F for ; Fri, 7 Jan 2022 10:18:16 -0800 (PST) Received: by mail-yb1-xb2b.google.com with SMTP id d1so19051566ybh.6 for ; Fri, 07 Jan 2022 10:18:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=m6dcpQatpjeU845+ufvzQySgxRZD48bb6LyjJ3DclOI=; b=l5cwDvVHxY1j1Hn4kDP2e8sdIWNedk8zfLjO7wQOWxDYdXoW9KdNKxbK+03HNQgEjF 13oJ+2oNuiu3tHfwKBYJZquyo9OAMQ21kSRF/YttoFh7nAkrWkrv+objlzlZhvSD//ut fGh6U1Ing0v8x5sZo4zp0AS9Xe02n9dYWYJBWRdV0OuM28M01+pthZnpexkh498DgTGL f/G/SbIwqUJTljB0jWNRKpJ8neeut2iHyB6rQ3Z6/GoLgMRi8HcIccoVVgI98kKi8FAH OQPv0+NHraFMsbeRy5mKWijFLCkhCZyq9IToQ7wIl3DMlFWlauQzCV3oV3+Tc5wzMX7F ejTg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=m6dcpQatpjeU845+ufvzQySgxRZD48bb6LyjJ3DclOI=; b=Znxxshj6bLHqdR1G8fvfH+uHcMDvaTc4gz0YYN28C/JvHvBYQ44RX4QAU1GFXlrLx7 6eMVyXAPHmhokoNZ8CaWZV9lt0VAziFDX6BvcUut67SK6FTY6HBwsAI6dDT43C+EylN5 hMLgQxA8QZvPA4P1pTU4ztIDzlFZnSIMT8LA4rGDALyPhPUv6APnTO2y3kP6lqenhjB3 8C8C3o6Wlv5gZcEUQ2gtIugLwwI4SLRybjudyPlhrzc6jM+CakZB2O0lB0AsSic9/RyV Zsqe2w1pULpXDtOGnMNETHM4jh6QvwvKWgOADYJB8Fz6e5OxfOAEqmdMObV3/ESIWIjA LHGw== X-Gm-Message-State: AOAM533nlTfIGZT1GFn8bxQFdIiv3Yg4kmy1Sxtt6mUjVhgwAay33+AV 6lNb45tIO5XHyBp6E8NZKv/82GELABZ6frQ5fGDWkw== X-Google-Smtp-Source: ABdhPJzv/air1dcF1g15MIJpVIQvJ+4wuCCuwp4zxiBwWsSBhOJaqrGSg8sM2BAw5raTJYJAv2mNoaj4waGH0gYb7oQ= X-Received: by 2002:a25:db0e:: with SMTP id g14mr65350368ybf.322.1641579494968; Fri, 07 Jan 2022 10:18:14 -0800 (PST) MIME-Version: 1.0 References: <20220104235148.21320-1-hridya@google.com> <49b29081-42df-ffcd-8fea-bd819499ff1b@amd.com> <3a29914d-0c7b-1f10-49cb-dbc1cc6e52b0@amd.com> In-Reply-To: <3a29914d-0c7b-1f10-49cb-dbc1cc6e52b0@amd.com> From: Hridya Valsaraju Date: Fri, 7 Jan 2022 10:17:38 -0800 Message-ID: Subject: Re: [PATCH] dma-buf: Move sysfs work out of DMA-BUF export/release path To: =?UTF-8?Q?Christian_K=C3=B6nig?= Cc: Sumit Semwal , Daniel Vetter , Greg Kroah-Hartman , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, john.stultz@linaro.org, surenb@google.com, kaleshsingh@google.com, tjmercier@google.com, keescook@google.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 7, 2022 at 2:22 AM Christian K=C3=B6nig wrote: > > Am 06.01.22 um 20:04 schrieb Hridya Valsaraju: > > On Thu, Jan 6, 2022 at 12:59 AM Christian K=C3=B6nig > > wrote: > >> Am 05.01.22 um 00:51 schrieb Hridya Valsaraju: > >>> Recently, we noticed an issue where a process went into direct reclai= m > >>> while holding the kernfs rw semaphore for sysfs in write(exclusive) > >>> mode. This caused processes who were doing DMA-BUF exports and releas= es > >>> to go into uninterruptible sleep since they needed to acquire the sam= e > >>> semaphore for the DMA-BUF sysfs entry creation/deletion. In order to = avoid > >>> blocking DMA-BUF export/release for an indeterminate amount of time > >>> while another process is holding the sysfs rw semaphore in exclusive > >>> mode, this patch moves the per-buffer sysfs file creation/deleteion t= o > >>> a kthread. > >> Well I absolutely don't think that this is justified. > >> > >> You adding tons of complexity here just to avoid the overhead of > >> creating the sysfs files while exporting DMA-bufs which is an operatio= n > >> which should be done exactly once in the lifecycle for the most common > >> use case. > >> > >> Please explain further why that should be necessary. > > Hi Christian, > > > > We noticed that the issue sometimes causes the exporting process to go > > to the uninterrupted sleep state for tens of milliseconds which > > unfortunately leads to user-perceptible UI jank. This is the reason > > why we are trying to move the sysfs entry creation and deletion out of > > the DMA-BUF export/release path. I will update the commit message to > > include the same in the next revision. > > That is still not a justification for this change. The question is why > do you need that in the first place? > > Exporting a DMA-buf should be something would should be very rarely, > e.g. only at the start of an application. Hi Christian, Yes, that is correct. Noticeable jank caused by the issue is not present at all times and happens on UI transitions(for example during app launches and exits) when there are several DMA-BUFs being exported and released. This is especially true in the case of the camera app since it exports and releases a relatively larger number of DMA-BUFs during launch and exit respectively. Regards, Hridya > > So this strongly looks like you are trying to optimize for an use case > where we should probably rethink what userspace is doing here instead. > > If we would want to go down this route you would need to change all the > drivers implementing the DMA-buf export functionality to avoid > uninterruptible sleep as well and that is certainly something I would NAK= . > > Regards, > Christian. > > > > > Thanks, > > Hridya > > > > > >> Regards, > >> Christian. > >> > >>> Fixes: bdb8d06dfefd ("dmabuf: Add the capability to expose DMA-BUF st= ats in sysfs") > >>> Signed-off-by: Hridya Valsaraju > >>> --- > >>> drivers/dma-buf/dma-buf-sysfs-stats.c | 343 ++++++++++++++++++++++= ++-- > >>> include/linux/dma-buf.h | 46 ++++ > >>> 2 files changed, 366 insertions(+), 23 deletions(-) > >>> > >>> diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.c b/drivers/dma-buf/= dma-buf-sysfs-stats.c > >>> index 053baadcada9..3251fdf2f05f 100644 > >>> --- a/drivers/dma-buf/dma-buf-sysfs-stats.c > >>> +++ b/drivers/dma-buf/dma-buf-sysfs-stats.c > >>> @@ -7,13 +7,39 @@ > >>> > >>> #include > >>> #include > >>> +#include > >>> #include > >>> +#include > >>> +#include > >>> #include > >>> +#include > >>> #include > >>> #include > >>> > >>> #include "dma-buf-sysfs-stats.h" > >>> > >>> +struct dmabuf_kobj_work { > >>> + struct list_head list; > >>> + struct dma_buf_sysfs_entry *sysfs_entry; > >>> + struct dma_buf_sysfs_entry_metadata *sysfs_metadata; > >>> + unsigned long uid; > >>> +}; > >>> + > >>> +/* Both kobject setup and teardown work gets queued on the list. */ > >>> +static LIST_HEAD(dmabuf_kobj_work_list); > >>> + > >>> +/* dmabuf_kobj_list_lock protects dmabuf_kobj_work_list. */ > >>> +static DEFINE_SPINLOCK(dmabuf_kobj_list_lock); > >>> + > >>> +/* > >>> + * dmabuf_sysfs_show_lock prevents a race between a DMA-BUF sysfs fi= le being > >>> + * read and the DMA-BUF being freed by protecting sysfs_entry->dmabu= f. > >>> + */ > >>> +static DEFINE_SPINLOCK(dmabuf_sysfs_show_lock); > >>> + > >>> +static struct task_struct *dmabuf_kobject_task; > >>> +static wait_queue_head_t dmabuf_kobject_waitqueue; > >>> + > >>> #define to_dma_buf_entry_from_kobj(x) container_of(x, struct dma_b= uf_sysfs_entry, kobj) > >>> > >>> /** > >>> @@ -64,15 +90,26 @@ static ssize_t dma_buf_stats_attribute_show(struc= t kobject *kobj, > >>> struct dma_buf_stats_attribute *attribute; > >>> struct dma_buf_sysfs_entry *sysfs_entry; > >>> struct dma_buf *dmabuf; > >>> + int ret; > >>> > >>> attribute =3D to_dma_buf_stats_attr(attr); > >>> sysfs_entry =3D to_dma_buf_entry_from_kobj(kobj); > >>> + > >>> + /* > >>> + * acquire dmabuf_sysfs_show_lock to prevent a race with the DM= A-BUF > >>> + * being freed while sysfs_entry->dmabuf is being accessed. > >>> + */ > >>> + spin_lock(&dmabuf_sysfs_show_lock); > >>> dmabuf =3D sysfs_entry->dmabuf; > >>> > >>> - if (!dmabuf || !attribute->show) > >>> + if (!dmabuf || !attribute->show) { > >>> + spin_unlock(&dmabuf_sysfs_show_lock); > >>> return -EIO; > >>> + } > >>> > >>> - return attribute->show(dmabuf, attribute, buf); > >>> + ret =3D attribute->show(dmabuf, attribute, buf); > >>> + spin_unlock(&dmabuf_sysfs_show_lock); > >>> + return ret; > >>> } > >>> > >>> static const struct sysfs_ops dma_buf_stats_sysfs_ops =3D { > >>> @@ -118,33 +155,275 @@ static struct kobj_type dma_buf_ktype =3D { > >>> .default_groups =3D dma_buf_stats_default_groups, > >>> }; > >>> > >>> -void dma_buf_stats_teardown(struct dma_buf *dmabuf) > >>> +/* Statistics files do not need to send uevents. */ > >>> +static int dmabuf_sysfs_uevent_filter(struct kset *kset, struct kobj= ect *kobj) > >>> { > >>> - struct dma_buf_sysfs_entry *sysfs_entry; > >>> + return 0; > >>> +} > >>> > >>> - sysfs_entry =3D dmabuf->sysfs_entry; > >>> - if (!sysfs_entry) > >>> - return; > >>> +static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops =3D { > >>> + .filter =3D dmabuf_sysfs_uevent_filter, > >>> +}; > >>> + > >>> +/* setup of sysfs entries done asynchronously in the worker thread. = */ > >>> +static void dma_buf_sysfs_stats_setup_work(struct dmabuf_kobj_work *= kobject_work) > >>> +{ > >>> + struct dma_buf_sysfs_entry *sysfs_entry =3D kobject_work->sysfs= _entry; > >>> + struct dma_buf_sysfs_entry_metadata *sysfs_metadata =3D > >>> + kobject_work->sysfs_metadata; > >>> + bool free_metadata =3D false; > >>> + > >>> + int ret =3D kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_k= type, NULL, > >>> + "%lu", kobject_work->uid); > >>> + if (ret) { > >>> + kobject_put(&sysfs_entry->kobj); > >>> + > >>> + spin_lock(&sysfs_metadata->sysfs_entry_lock); > >>> + if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_INIT_ABOR= TED) { > >>> + /* > >>> + * SYSFS_ENTRY_INIT_ABORTED means that the DMA-= BUF has already > >>> + * been freed. At this point, its safe to free = the memory for > >>> + * the sysfs_metadata; > >>> + */ > >>> + free_metadata =3D true; > >>> + } else { > >>> + /* > >>> + * The DMA-BUF has not yet been freed, set the = status to > >>> + * sysfs_entry_error so that when the DMA-BUF g= ets > >>> + * freed, we know there is no need to teardown = the sysfs > >>> + * entry. > >>> + */ > >>> + sysfs_metadata->status =3D SYSFS_ENTRY_ERROR; > >>> + } > >>> + goto unlock; > >>> + } > >>> + > >>> + /* > >>> + * If the DMA-BUF has not yet been released, status would still= be > >>> + * SYSFS_ENTRY_INIT_IN_PROGRESS. We set the status as initializ= ed. > >>> + */ > >>> + spin_lock(&sysfs_metadata->sysfs_entry_lock); > >>> + if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_INIT_IN_PROGRESS)= { > >>> + sysfs_metadata->status =3D SYSFS_ENTRY_INITIALIZED; > >>> + goto unlock; > >>> + } > >>> > >>> + /* > >>> + * At this point the status is SYSFS_ENTRY_INIT_ABORTED which m= eans > >>> + * that the DMA-BUF has already been freed. Hence, we cleanup t= he > >>> + * sysfs_entry and its metadata since neither of them are neede= d > >>> + * anymore. > >>> + */ > >>> + free_metadata =3D true; > >>> kobject_del(&sysfs_entry->kobj); > >>> kobject_put(&sysfs_entry->kobj); > >>> + > >>> +unlock: > >>> + spin_unlock(&sysfs_metadata->sysfs_entry_lock); > >>> + if (free_metadata) { > >>> + kfree(kobject_work->sysfs_metadata); > >>> + kobject_work->sysfs_metadata =3D NULL; > >>> + } > >>> } > >>> > >>> +/* teardown of sysfs entries done asynchronously in the worker threa= d. */ > >>> +static void dma_buf_sysfs_stats_teardown_work(struct dmabuf_kobj_wor= k *kobject_work) > >>> +{ > >>> + struct dma_buf_sysfs_entry *sysfs_entry =3D kobject_work->sysfs= _entry; > >>> > >>> -/* Statistics files do not need to send uevents. */ > >>> -static int dmabuf_sysfs_uevent_filter(struct kset *kset, struct kobj= ect *kobj) > >>> + kobject_del(&sysfs_entry->kobj); > >>> + kobject_put(&sysfs_entry->kobj); > >>> + > >>> + kfree(kobject_work->sysfs_metadata); > >>> + kobject_work->sysfs_metadata =3D NULL; > >>> +} > >>> + > >>> +/* do setup or teardown of sysfs entries as required */ > >>> +static void do_kobject_work(struct dmabuf_kobj_work *kobject_work) > >>> { > >>> + struct dma_buf_sysfs_entry_metadata *sysfs_metadata; > >>> + bool setup_needed =3D false; > >>> + bool teardown_needed =3D false; > >>> + > >>> + sysfs_metadata =3D kobject_work->sysfs_metadata; > >>> + spin_lock(&sysfs_metadata->sysfs_entry_lock); > >>> + if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_UNINITIALIZED) { > >>> + setup_needed =3D true; > >>> + sysfs_metadata->status =3D SYSFS_ENTRY_INIT_IN_PROGRESS= ; > >>> + } else if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_INITIALIZE= D) { > >>> + teardown_needed =3D true; > >>> + } > >>> + > >>> + /* > >>> + * It is ok to release the sysfs_entry_lock here. > >>> + * > >>> + * If setup_needed is true, we check the status again after the= kobject > >>> + * initialization to see if it has been set to SYSFS_ENTRY_INIT= _ABORTED > >>> + * and if so teardown the kobject. > >>> + * > >>> + * If teardown_needed is true, there are no more changes expect= ed to the > >>> + * status. > >>> + * > >>> + * If neither setup_needed nor teardown needed are true, it > >>> + * means the DMA-BUF was freed before we got around to setting = up the > >>> + * sysfs entry and hence we just need to release the metadata a= nd > >>> + * return. > >>> + */ > >>> + spin_unlock(&kobject_work->sysfs_metadata->sysfs_entry_lock); > >>> + > >>> + if (setup_needed) > >>> + dma_buf_sysfs_stats_setup_work(kobject_work); > >>> + else if (teardown_needed) > >>> + dma_buf_sysfs_stats_teardown_work(kobject_work); > >>> + else > >>> + kfree(kobject_work->sysfs_metadata); > >>> + > >>> + kfree(kobject_work); > >>> +} > >>> + > >>> +static struct dmabuf_kobj_work *get_next_kobj_work(void) > >>> +{ > >>> + struct dmabuf_kobj_work *kobject_work; > >>> + > >>> + spin_lock(&dmabuf_kobj_list_lock); > >>> + kobject_work =3D list_first_entry_or_null(&dmabuf_kobj_work_lis= t, > >>> + struct dmabuf_kobj_work= , list); > >>> + if (kobject_work) > >>> + list_del(&kobject_work->list); > >>> + spin_unlock(&dmabuf_kobj_list_lock); > >>> + return kobject_work; > >>> +} > >>> + > >>> +static int kobject_work_thread(void *data) > >>> +{ > >>> + struct dmabuf_kobj_work *kobject_work; > >>> + > >>> + while (1) { > >>> + wait_event_freezable(dmabuf_kobject_waitqueue, > >>> + (kobject_work =3D get_next_kobj_wo= rk())); > >>> + do_kobject_work(kobject_work); > >>> + } > >>> + > >>> return 0; > >>> } > >>> > >>> -static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops =3D { > >>> - .filter =3D dmabuf_sysfs_uevent_filter, > >>> -}; > >>> +static int kobject_worklist_init(void) > >>> +{ > >>> + init_waitqueue_head(&dmabuf_kobject_waitqueue); > >>> + dmabuf_kobject_task =3D kthread_run(kobject_work_thread, NULL, > >>> + "%s", "dmabuf-kobject-worker"= ); > >>> + if (IS_ERR(dmabuf_kobject_task)) { > >>> + pr_err("Creating thread for deferred sysfs entry creati= on/deletion failed\n"); > >>> + return PTR_ERR(dmabuf_kobject_task); > >>> + } > >>> + sched_set_normal(dmabuf_kobject_task, MAX_NICE); > >>> + > >>> + return 0; > >>> +} > >>> + > >>> +static void deferred_kobject_create(struct dmabuf_kobj_work *kobject= _work) > >>> +{ > >>> + INIT_LIST_HEAD(&kobject_work->list); > >>> + > >>> + spin_lock(&dmabuf_kobj_list_lock); > >>> + > >>> + list_add_tail(&kobject_work->list, &dmabuf_kobj_work_list); > >>> + > >>> + spin_unlock(&dmabuf_kobj_list_lock); > >>> + > >>> + wake_up(&dmabuf_kobject_waitqueue); > >>> +} > >>> + > >>> + > >>> +void dma_buf_stats_teardown(struct dma_buf *dmabuf) > >>> +{ > >>> + struct dma_buf_sysfs_entry *sysfs_entry; > >>> + struct dma_buf_sysfs_entry_metadata *sysfs_metadata; > >>> + struct dmabuf_kobj_work *kobj_work; > >>> + > >>> + sysfs_entry =3D dmabuf->sysfs_entry; > >>> + if (!sysfs_entry) > >>> + return; > >>> + > >>> + sysfs_metadata =3D dmabuf->sysfs_entry_metadata; > >>> + if (!sysfs_metadata) > >>> + return; > >>> + > >>> + spin_lock(&sysfs_metadata->sysfs_entry_lock); > >>> + > >>> + if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_UNINITIALIZED || > >>> + sysfs_metadata->status =3D=3D SYSFS_ENTRY_INIT_IN_PROGRESS)= { > >>> + /* > >>> + * The sysfs entry for this buffer has not yet been ini= tialized, > >>> + * we set the status to SYSFS_ENTRY_INIT_ABORTED to abo= rt the > >>> + * initialization. > >>> + */ > >>> + sysfs_metadata->status =3D SYSFS_ENTRY_INIT_ABORTED; > >>> + spin_unlock(&sysfs_metadata->sysfs_entry_lock); > >>> + > >>> + /* > >>> + * In case kobject initialization completes right as we= release > >>> + * the sysfs_entry_lock, disable show() for the sysfs e= ntry by > >>> + * setting sysfs_entry->dmabuf to NULL to prevent a rac= e. > >>> + */ > >>> + spin_lock(&dmabuf_sysfs_show_lock); > >>> + sysfs_entry->dmabuf =3D NULL; > >>> + spin_unlock(&dmabuf_sysfs_show_lock); > >>> + > >>> + return; > >>> + } > >>> + > >>> + if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_INITIALIZED) { > >>> + /* > >>> + * queue teardown work only if sysfs_entry is fully ini= titalized. > >>> + * It is ok to release the sysfs_entry_lock here since = the > >>> + * status can no longer change. > >>> + */ > >>> + spin_unlock(&sysfs_metadata->sysfs_entry_lock); > >>> + > >>> + /* > >>> + * Meanwhile disable show() for the sysfs entry to avoi= d a race > >>> + * between teardown and show(). > >>> + */ > >>> + spin_lock(&dmabuf_sysfs_show_lock); > >>> + sysfs_entry->dmabuf =3D NULL; > >>> + spin_unlock(&dmabuf_sysfs_show_lock); > >>> + > >>> + kobj_work =3D kzalloc(sizeof(struct dmabuf_kobj_work), = GFP_KERNEL); > >>> + if (!kobj_work) { > >>> + /* do the teardown immediately. */ > >>> + kobject_del(&sysfs_entry->kobj); > >>> + kobject_put(&sysfs_entry->kobj); > >>> + kfree(sysfs_metadata); > >>> + } else { > >>> + /* queue teardown work. */ > >>> + kobj_work->sysfs_entry =3D dmabuf->sysfs_entry; > >>> + kobj_work->sysfs_metadata =3D dmabuf->sysfs_ent= ry_metadata; > >>> + deferred_kobject_create(kobj_work); > >>> + } > >>> + > >>> + return; > >>> + } > >>> + > >>> + /* > >>> + * status is SYSFS_ENTRY_INIT_ERROR so we only need to free the > >>> + * metadata. > >>> + */ > >>> + spin_unlock(&sysfs_metadata->sysfs_entry_lock); > >>> + kfree(dmabuf->sysfs_entry_metadata); > >>> + dmabuf->sysfs_entry_metadata =3D NULL; > >>> +} > >>> > >>> static struct kset *dma_buf_stats_kset; > >>> static struct kset *dma_buf_per_buffer_stats_kset; > >>> int dma_buf_init_sysfs_statistics(void) > >>> { > >>> + int ret; > >>> + > >>> + ret =3D kobject_worklist_init(); > >>> + if (ret) > >>> + return ret; > >>> + > >>> dma_buf_stats_kset =3D kset_create_and_add("dmabuf", > >>> &dmabuf_sysfs_no_ueve= nt_ops, > >>> kernel_kobj); > >>> @@ -171,7 +450,8 @@ void dma_buf_uninit_sysfs_statistics(void) > >>> int dma_buf_stats_setup(struct dma_buf *dmabuf) > >>> { > >>> struct dma_buf_sysfs_entry *sysfs_entry; > >>> - int ret; > >>> + struct dma_buf_sysfs_entry_metadata *sysfs_metadata; > >>> + struct dmabuf_kobj_work *kobj_work; > >>> > >>> if (!dmabuf || !dmabuf->file) > >>> return -EINVAL; > >>> @@ -188,18 +468,35 @@ int dma_buf_stats_setup(struct dma_buf *dmabuf) > >>> sysfs_entry->kobj.kset =3D dma_buf_per_buffer_stats_kset; > >>> sysfs_entry->dmabuf =3D dmabuf; > >>> > >>> + sysfs_metadata =3D kzalloc(sizeof(struct dma_buf_sysfs_entry_me= tadata), > >>> + GFP_KERNEL); > >>> + if (!sysfs_metadata) { > >>> + kfree(sysfs_entry); > >>> + return -ENOMEM; > >>> + } > >>> + > >>> dmabuf->sysfs_entry =3D sysfs_entry; > >>> > >>> - /* create the directory for buffer stats */ > >>> - ret =3D kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_ktype= , NULL, > >>> - "%lu", file_inode(dmabuf->file)->i_i= no); > >>> - if (ret) > >>> - goto err_sysfs_dmabuf; > >>> + sysfs_metadata->status =3D SYSFS_ENTRY_UNINITIALIZED; > >>> + spin_lock_init(&sysfs_metadata->sysfs_entry_lock); > >>> > >>> - return 0; > >>> + dmabuf->sysfs_entry_metadata =3D sysfs_metadata; > >>> > >>> -err_sysfs_dmabuf: > >>> - kobject_put(&sysfs_entry->kobj); > >>> - dmabuf->sysfs_entry =3D NULL; > >>> - return ret; > >>> + kobj_work =3D kzalloc(sizeof(struct dmabuf_kobj_work), GFP_KERN= EL); > >>> + if (!kobj_work) { > >>> + kfree(sysfs_entry); > >>> + kfree(sysfs_metadata); > >>> + return -ENOMEM; > >>> + } > >>> + > >>> + kobj_work->sysfs_entry =3D dmabuf->sysfs_entry; > >>> + kobj_work->sysfs_metadata =3D dmabuf->sysfs_entry_metadata; > >>> + /* > >>> + * stash the inode number in struct dmabuf_kobj_work since setu= p > >>> + * might race with DMA-BUF teardown. > >>> + */ > >>> + kobj_work->uid =3D file_inode(dmabuf->file)->i_ino; > >>> + > >>> + deferred_kobject_create(kobj_work); > >>> + return 0; > >>> } > >>> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h > >>> index 7ab50076e7a6..0597690023a0 100644 > >>> --- a/include/linux/dma-buf.h > >>> +++ b/include/linux/dma-buf.h > >>> @@ -287,6 +287,50 @@ struct dma_buf_ops { > >>> void (*vunmap)(struct dma_buf *dmabuf, struct dma_buf_map *map= ); > >>> }; > >>> > >>> +#ifdef CONFIG_DMABUF_SYSFS_STATS > >>> +enum sysfs_entry_status { > >>> + SYSFS_ENTRY_UNINITIALIZED, > >>> + SYSFS_ENTRY_INIT_IN_PROGRESS, > >>> + SYSFS_ENTRY_ERROR, > >>> + SYSFS_ENTRY_INIT_ABORTED, > >>> + SYSFS_ENTRY_INITIALIZED, > >>> +}; > >>> + > >>> +/* > >>> + * struct dma_buf_sysfs_entry_metadata - Holds the current status fo= r the > >>> + * DMA-BUF sysfs entry. > >>> + * > >>> + * @status: holds the current status for the DMA-BUF sysfs entry. Th= e status of > >>> + * the sysfs entry has the following path. > >>> + * > >>> + * SYSFS_ENTRY_UNINITIALIZED > >>> + * __________________|____________________ > >>> + * | | > >>> + * SYSFS_ENTRY_INIT_IN_PROGRESS SYSFS_ENTRY_INIT_ABORTED (D= MA-BUF > >>> + * | g= ets freed > >>> + * | b= efore > >>> + * | i= nit) > >>> + * ________|_____________________________________ > >>> + * | | | > >>> + * SYSFS_ENTRY_INITIALIZED | SYSFS_ENTRY_INIT_ABORTED > >>> + * | (DMA-BUF gets freed d= uring kobject > >>> + * | init) > >>> + * | > >>> + * | > >>> + * SYSFS_ENTRY_ERROR > >>> + * (error during kobject init) > >>> + * > >>> + * @sysfs_entry_lock: protects access to @status. > >>> + */ > >>> +struct dma_buf_sysfs_entry_metadata { > >>> + enum sysfs_entry_status status; > >>> + /* > >>> + * Protects sysfs_entry_metadata->status > >>> + */ > >>> + spinlock_t sysfs_entry_lock; > >>> +}; > >>> +#endif > >>> + > >>> /** > >>> * struct dma_buf - shared buffer object > >>> * > >>> @@ -452,6 +496,8 @@ struct dma_buf { > >>> struct kobject kobj; > >>> struct dma_buf *dmabuf; > >>> } *sysfs_entry; > >>> + > >>> + struct dma_buf_sysfs_entry_metadata *sysfs_entry_metadata; > >>> #endif > >>> }; > >>> > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5B3A7C433EF for ; Fri, 7 Jan 2022 18:18:18 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 27DBD10E8EF; Fri, 7 Jan 2022 18:18:17 +0000 (UTC) Received: from mail-yb1-xb2f.google.com (mail-yb1-xb2f.google.com [IPv6:2607:f8b0:4864:20::b2f]) by gabe.freedesktop.org (Postfix) with ESMTPS id 2CE8B10E8EF for ; Fri, 7 Jan 2022 18:18:16 +0000 (UTC) Received: by mail-yb1-xb2f.google.com with SMTP id y130so19047866ybe.8 for ; 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Fri, 07 Jan 2022 10:18:14 -0800 (PST) MIME-Version: 1.0 References: <20220104235148.21320-1-hridya@google.com> <49b29081-42df-ffcd-8fea-bd819499ff1b@amd.com> <3a29914d-0c7b-1f10-49cb-dbc1cc6e52b0@amd.com> In-Reply-To: <3a29914d-0c7b-1f10-49cb-dbc1cc6e52b0@amd.com> From: Hridya Valsaraju Date: Fri, 7 Jan 2022 10:17:38 -0800 Message-ID: Subject: Re: [PATCH] dma-buf: Move sysfs work out of DMA-BUF export/release path To: =?UTF-8?Q?Christian_K=C3=B6nig?= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: keescook@google.com, Daniel Vetter , kaleshsingh@google.com, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, tjmercier@google.com, linaro-mm-sig@lists.linaro.org, Greg Kroah-Hartman , surenb@google.com, linux-media@vger.kernel.org Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Fri, Jan 7, 2022 at 2:22 AM Christian K=C3=B6nig wrote: > > Am 06.01.22 um 20:04 schrieb Hridya Valsaraju: > > On Thu, Jan 6, 2022 at 12:59 AM Christian K=C3=B6nig > > wrote: > >> Am 05.01.22 um 00:51 schrieb Hridya Valsaraju: > >>> Recently, we noticed an issue where a process went into direct reclai= m > >>> while holding the kernfs rw semaphore for sysfs in write(exclusive) > >>> mode. This caused processes who were doing DMA-BUF exports and releas= es > >>> to go into uninterruptible sleep since they needed to acquire the sam= e > >>> semaphore for the DMA-BUF sysfs entry creation/deletion. In order to = avoid > >>> blocking DMA-BUF export/release for an indeterminate amount of time > >>> while another process is holding the sysfs rw semaphore in exclusive > >>> mode, this patch moves the per-buffer sysfs file creation/deleteion t= o > >>> a kthread. > >> Well I absolutely don't think that this is justified. > >> > >> You adding tons of complexity here just to avoid the overhead of > >> creating the sysfs files while exporting DMA-bufs which is an operatio= n > >> which should be done exactly once in the lifecycle for the most common > >> use case. > >> > >> Please explain further why that should be necessary. > > Hi Christian, > > > > We noticed that the issue sometimes causes the exporting process to go > > to the uninterrupted sleep state for tens of milliseconds which > > unfortunately leads to user-perceptible UI jank. This is the reason > > why we are trying to move the sysfs entry creation and deletion out of > > the DMA-BUF export/release path. I will update the commit message to > > include the same in the next revision. > > That is still not a justification for this change. The question is why > do you need that in the first place? > > Exporting a DMA-buf should be something would should be very rarely, > e.g. only at the start of an application. Hi Christian, Yes, that is correct. Noticeable jank caused by the issue is not present at all times and happens on UI transitions(for example during app launches and exits) when there are several DMA-BUFs being exported and released. This is especially true in the case of the camera app since it exports and releases a relatively larger number of DMA-BUFs during launch and exit respectively. Regards, Hridya > > So this strongly looks like you are trying to optimize for an use case > where we should probably rethink what userspace is doing here instead. > > If we would want to go down this route you would need to change all the > drivers implementing the DMA-buf export functionality to avoid > uninterruptible sleep as well and that is certainly something I would NAK= . > > Regards, > Christian. > > > > > Thanks, > > Hridya > > > > > >> Regards, > >> Christian. > >> > >>> Fixes: bdb8d06dfefd ("dmabuf: Add the capability to expose DMA-BUF st= ats in sysfs") > >>> Signed-off-by: Hridya Valsaraju > >>> --- > >>> drivers/dma-buf/dma-buf-sysfs-stats.c | 343 ++++++++++++++++++++++= ++-- > >>> include/linux/dma-buf.h | 46 ++++ > >>> 2 files changed, 366 insertions(+), 23 deletions(-) > >>> > >>> diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.c b/drivers/dma-buf/= dma-buf-sysfs-stats.c > >>> index 053baadcada9..3251fdf2f05f 100644 > >>> --- a/drivers/dma-buf/dma-buf-sysfs-stats.c > >>> +++ b/drivers/dma-buf/dma-buf-sysfs-stats.c > >>> @@ -7,13 +7,39 @@ > >>> > >>> #include > >>> #include > >>> +#include > >>> #include > >>> +#include > >>> +#include > >>> #include > >>> +#include > >>> #include > >>> #include > >>> > >>> #include "dma-buf-sysfs-stats.h" > >>> > >>> +struct dmabuf_kobj_work { > >>> + struct list_head list; > >>> + struct dma_buf_sysfs_entry *sysfs_entry; > >>> + struct dma_buf_sysfs_entry_metadata *sysfs_metadata; > >>> + unsigned long uid; > >>> +}; > >>> + > >>> +/* Both kobject setup and teardown work gets queued on the list. */ > >>> +static LIST_HEAD(dmabuf_kobj_work_list); > >>> + > >>> +/* dmabuf_kobj_list_lock protects dmabuf_kobj_work_list. */ > >>> +static DEFINE_SPINLOCK(dmabuf_kobj_list_lock); > >>> + > >>> +/* > >>> + * dmabuf_sysfs_show_lock prevents a race between a DMA-BUF sysfs fi= le being > >>> + * read and the DMA-BUF being freed by protecting sysfs_entry->dmabu= f. > >>> + */ > >>> +static DEFINE_SPINLOCK(dmabuf_sysfs_show_lock); > >>> + > >>> +static struct task_struct *dmabuf_kobject_task; > >>> +static wait_queue_head_t dmabuf_kobject_waitqueue; > >>> + > >>> #define to_dma_buf_entry_from_kobj(x) container_of(x, struct dma_b= uf_sysfs_entry, kobj) > >>> > >>> /** > >>> @@ -64,15 +90,26 @@ static ssize_t dma_buf_stats_attribute_show(struc= t kobject *kobj, > >>> struct dma_buf_stats_attribute *attribute; > >>> struct dma_buf_sysfs_entry *sysfs_entry; > >>> struct dma_buf *dmabuf; > >>> + int ret; > >>> > >>> attribute =3D to_dma_buf_stats_attr(attr); > >>> sysfs_entry =3D to_dma_buf_entry_from_kobj(kobj); > >>> + > >>> + /* > >>> + * acquire dmabuf_sysfs_show_lock to prevent a race with the DM= A-BUF > >>> + * being freed while sysfs_entry->dmabuf is being accessed. > >>> + */ > >>> + spin_lock(&dmabuf_sysfs_show_lock); > >>> dmabuf =3D sysfs_entry->dmabuf; > >>> > >>> - if (!dmabuf || !attribute->show) > >>> + if (!dmabuf || !attribute->show) { > >>> + spin_unlock(&dmabuf_sysfs_show_lock); > >>> return -EIO; > >>> + } > >>> > >>> - return attribute->show(dmabuf, attribute, buf); > >>> + ret =3D attribute->show(dmabuf, attribute, buf); > >>> + spin_unlock(&dmabuf_sysfs_show_lock); > >>> + return ret; > >>> } > >>> > >>> static const struct sysfs_ops dma_buf_stats_sysfs_ops =3D { > >>> @@ -118,33 +155,275 @@ static struct kobj_type dma_buf_ktype =3D { > >>> .default_groups =3D dma_buf_stats_default_groups, > >>> }; > >>> > >>> -void dma_buf_stats_teardown(struct dma_buf *dmabuf) > >>> +/* Statistics files do not need to send uevents. */ > >>> +static int dmabuf_sysfs_uevent_filter(struct kset *kset, struct kobj= ect *kobj) > >>> { > >>> - struct dma_buf_sysfs_entry *sysfs_entry; > >>> + return 0; > >>> +} > >>> > >>> - sysfs_entry =3D dmabuf->sysfs_entry; > >>> - if (!sysfs_entry) > >>> - return; > >>> +static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops =3D { > >>> + .filter =3D dmabuf_sysfs_uevent_filter, > >>> +}; > >>> + > >>> +/* setup of sysfs entries done asynchronously in the worker thread. = */ > >>> +static void dma_buf_sysfs_stats_setup_work(struct dmabuf_kobj_work *= kobject_work) > >>> +{ > >>> + struct dma_buf_sysfs_entry *sysfs_entry =3D kobject_work->sysfs= _entry; > >>> + struct dma_buf_sysfs_entry_metadata *sysfs_metadata =3D > >>> + kobject_work->sysfs_metadata; > >>> + bool free_metadata =3D false; > >>> + > >>> + int ret =3D kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_k= type, NULL, > >>> + "%lu", kobject_work->uid); > >>> + if (ret) { > >>> + kobject_put(&sysfs_entry->kobj); > >>> + > >>> + spin_lock(&sysfs_metadata->sysfs_entry_lock); > >>> + if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_INIT_ABOR= TED) { > >>> + /* > >>> + * SYSFS_ENTRY_INIT_ABORTED means that the DMA-= BUF has already > >>> + * been freed. At this point, its safe to free = the memory for > >>> + * the sysfs_metadata; > >>> + */ > >>> + free_metadata =3D true; > >>> + } else { > >>> + /* > >>> + * The DMA-BUF has not yet been freed, set the = status to > >>> + * sysfs_entry_error so that when the DMA-BUF g= ets > >>> + * freed, we know there is no need to teardown = the sysfs > >>> + * entry. > >>> + */ > >>> + sysfs_metadata->status =3D SYSFS_ENTRY_ERROR; > >>> + } > >>> + goto unlock; > >>> + } > >>> + > >>> + /* > >>> + * If the DMA-BUF has not yet been released, status would still= be > >>> + * SYSFS_ENTRY_INIT_IN_PROGRESS. We set the status as initializ= ed. > >>> + */ > >>> + spin_lock(&sysfs_metadata->sysfs_entry_lock); > >>> + if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_INIT_IN_PROGRESS)= { > >>> + sysfs_metadata->status =3D SYSFS_ENTRY_INITIALIZED; > >>> + goto unlock; > >>> + } > >>> > >>> + /* > >>> + * At this point the status is SYSFS_ENTRY_INIT_ABORTED which m= eans > >>> + * that the DMA-BUF has already been freed. Hence, we cleanup t= he > >>> + * sysfs_entry and its metadata since neither of them are neede= d > >>> + * anymore. > >>> + */ > >>> + free_metadata =3D true; > >>> kobject_del(&sysfs_entry->kobj); > >>> kobject_put(&sysfs_entry->kobj); > >>> + > >>> +unlock: > >>> + spin_unlock(&sysfs_metadata->sysfs_entry_lock); > >>> + if (free_metadata) { > >>> + kfree(kobject_work->sysfs_metadata); > >>> + kobject_work->sysfs_metadata =3D NULL; > >>> + } > >>> } > >>> > >>> +/* teardown of sysfs entries done asynchronously in the worker threa= d. */ > >>> +static void dma_buf_sysfs_stats_teardown_work(struct dmabuf_kobj_wor= k *kobject_work) > >>> +{ > >>> + struct dma_buf_sysfs_entry *sysfs_entry =3D kobject_work->sysfs= _entry; > >>> > >>> -/* Statistics files do not need to send uevents. */ > >>> -static int dmabuf_sysfs_uevent_filter(struct kset *kset, struct kobj= ect *kobj) > >>> + kobject_del(&sysfs_entry->kobj); > >>> + kobject_put(&sysfs_entry->kobj); > >>> + > >>> + kfree(kobject_work->sysfs_metadata); > >>> + kobject_work->sysfs_metadata =3D NULL; > >>> +} > >>> + > >>> +/* do setup or teardown of sysfs entries as required */ > >>> +static void do_kobject_work(struct dmabuf_kobj_work *kobject_work) > >>> { > >>> + struct dma_buf_sysfs_entry_metadata *sysfs_metadata; > >>> + bool setup_needed =3D false; > >>> + bool teardown_needed =3D false; > >>> + > >>> + sysfs_metadata =3D kobject_work->sysfs_metadata; > >>> + spin_lock(&sysfs_metadata->sysfs_entry_lock); > >>> + if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_UNINITIALIZED) { > >>> + setup_needed =3D true; > >>> + sysfs_metadata->status =3D SYSFS_ENTRY_INIT_IN_PROGRESS= ; > >>> + } else if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_INITIALIZE= D) { > >>> + teardown_needed =3D true; > >>> + } > >>> + > >>> + /* > >>> + * It is ok to release the sysfs_entry_lock here. > >>> + * > >>> + * If setup_needed is true, we check the status again after the= kobject > >>> + * initialization to see if it has been set to SYSFS_ENTRY_INIT= _ABORTED > >>> + * and if so teardown the kobject. > >>> + * > >>> + * If teardown_needed is true, there are no more changes expect= ed to the > >>> + * status. > >>> + * > >>> + * If neither setup_needed nor teardown needed are true, it > >>> + * means the DMA-BUF was freed before we got around to setting = up the > >>> + * sysfs entry and hence we just need to release the metadata a= nd > >>> + * return. > >>> + */ > >>> + spin_unlock(&kobject_work->sysfs_metadata->sysfs_entry_lock); > >>> + > >>> + if (setup_needed) > >>> + dma_buf_sysfs_stats_setup_work(kobject_work); > >>> + else if (teardown_needed) > >>> + dma_buf_sysfs_stats_teardown_work(kobject_work); > >>> + else > >>> + kfree(kobject_work->sysfs_metadata); > >>> + > >>> + kfree(kobject_work); > >>> +} > >>> + > >>> +static struct dmabuf_kobj_work *get_next_kobj_work(void) > >>> +{ > >>> + struct dmabuf_kobj_work *kobject_work; > >>> + > >>> + spin_lock(&dmabuf_kobj_list_lock); > >>> + kobject_work =3D list_first_entry_or_null(&dmabuf_kobj_work_lis= t, > >>> + struct dmabuf_kobj_work= , list); > >>> + if (kobject_work) > >>> + list_del(&kobject_work->list); > >>> + spin_unlock(&dmabuf_kobj_list_lock); > >>> + return kobject_work; > >>> +} > >>> + > >>> +static int kobject_work_thread(void *data) > >>> +{ > >>> + struct dmabuf_kobj_work *kobject_work; > >>> + > >>> + while (1) { > >>> + wait_event_freezable(dmabuf_kobject_waitqueue, > >>> + (kobject_work =3D get_next_kobj_wo= rk())); > >>> + do_kobject_work(kobject_work); > >>> + } > >>> + > >>> return 0; > >>> } > >>> > >>> -static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops =3D { > >>> - .filter =3D dmabuf_sysfs_uevent_filter, > >>> -}; > >>> +static int kobject_worklist_init(void) > >>> +{ > >>> + init_waitqueue_head(&dmabuf_kobject_waitqueue); > >>> + dmabuf_kobject_task =3D kthread_run(kobject_work_thread, NULL, > >>> + "%s", "dmabuf-kobject-worker"= ); > >>> + if (IS_ERR(dmabuf_kobject_task)) { > >>> + pr_err("Creating thread for deferred sysfs entry creati= on/deletion failed\n"); > >>> + return PTR_ERR(dmabuf_kobject_task); > >>> + } > >>> + sched_set_normal(dmabuf_kobject_task, MAX_NICE); > >>> + > >>> + return 0; > >>> +} > >>> + > >>> +static void deferred_kobject_create(struct dmabuf_kobj_work *kobject= _work) > >>> +{ > >>> + INIT_LIST_HEAD(&kobject_work->list); > >>> + > >>> + spin_lock(&dmabuf_kobj_list_lock); > >>> + > >>> + list_add_tail(&kobject_work->list, &dmabuf_kobj_work_list); > >>> + > >>> + spin_unlock(&dmabuf_kobj_list_lock); > >>> + > >>> + wake_up(&dmabuf_kobject_waitqueue); > >>> +} > >>> + > >>> + > >>> +void dma_buf_stats_teardown(struct dma_buf *dmabuf) > >>> +{ > >>> + struct dma_buf_sysfs_entry *sysfs_entry; > >>> + struct dma_buf_sysfs_entry_metadata *sysfs_metadata; > >>> + struct dmabuf_kobj_work *kobj_work; > >>> + > >>> + sysfs_entry =3D dmabuf->sysfs_entry; > >>> + if (!sysfs_entry) > >>> + return; > >>> + > >>> + sysfs_metadata =3D dmabuf->sysfs_entry_metadata; > >>> + if (!sysfs_metadata) > >>> + return; > >>> + > >>> + spin_lock(&sysfs_metadata->sysfs_entry_lock); > >>> + > >>> + if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_UNINITIALIZED || > >>> + sysfs_metadata->status =3D=3D SYSFS_ENTRY_INIT_IN_PROGRESS)= { > >>> + /* > >>> + * The sysfs entry for this buffer has not yet been ini= tialized, > >>> + * we set the status to SYSFS_ENTRY_INIT_ABORTED to abo= rt the > >>> + * initialization. > >>> + */ > >>> + sysfs_metadata->status =3D SYSFS_ENTRY_INIT_ABORTED; > >>> + spin_unlock(&sysfs_metadata->sysfs_entry_lock); > >>> + > >>> + /* > >>> + * In case kobject initialization completes right as we= release > >>> + * the sysfs_entry_lock, disable show() for the sysfs e= ntry by > >>> + * setting sysfs_entry->dmabuf to NULL to prevent a rac= e. > >>> + */ > >>> + spin_lock(&dmabuf_sysfs_show_lock); > >>> + sysfs_entry->dmabuf =3D NULL; > >>> + spin_unlock(&dmabuf_sysfs_show_lock); > >>> + > >>> + return; > >>> + } > >>> + > >>> + if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_INITIALIZED) { > >>> + /* > >>> + * queue teardown work only if sysfs_entry is fully ini= titalized. > >>> + * It is ok to release the sysfs_entry_lock here since = the > >>> + * status can no longer change. > >>> + */ > >>> + spin_unlock(&sysfs_metadata->sysfs_entry_lock); > >>> + > >>> + /* > >>> + * Meanwhile disable show() for the sysfs entry to avoi= d a race > >>> + * between teardown and show(). > >>> + */ > >>> + spin_lock(&dmabuf_sysfs_show_lock); > >>> + sysfs_entry->dmabuf =3D NULL; > >>> + spin_unlock(&dmabuf_sysfs_show_lock); > >>> + > >>> + kobj_work =3D kzalloc(sizeof(struct dmabuf_kobj_work), = GFP_KERNEL); > >>> + if (!kobj_work) { > >>> + /* do the teardown immediately. */ > >>> + kobject_del(&sysfs_entry->kobj); > >>> + kobject_put(&sysfs_entry->kobj); > >>> + kfree(sysfs_metadata); > >>> + } else { > >>> + /* queue teardown work. */ > >>> + kobj_work->sysfs_entry =3D dmabuf->sysfs_entry; > >>> + kobj_work->sysfs_metadata =3D dmabuf->sysfs_ent= ry_metadata; > >>> + deferred_kobject_create(kobj_work); > >>> + } > >>> + > >>> + return; > >>> + } > >>> + > >>> + /* > >>> + * status is SYSFS_ENTRY_INIT_ERROR so we only need to free the > >>> + * metadata. > >>> + */ > >>> + spin_unlock(&sysfs_metadata->sysfs_entry_lock); > >>> + kfree(dmabuf->sysfs_entry_metadata); > >>> + dmabuf->sysfs_entry_metadata =3D NULL; > >>> +} > >>> > >>> static struct kset *dma_buf_stats_kset; > >>> static struct kset *dma_buf_per_buffer_stats_kset; > >>> int dma_buf_init_sysfs_statistics(void) > >>> { > >>> + int ret; > >>> + > >>> + ret =3D kobject_worklist_init(); > >>> + if (ret) > >>> + return ret; > >>> + > >>> dma_buf_stats_kset =3D kset_create_and_add("dmabuf", > >>> &dmabuf_sysfs_no_ueve= nt_ops, > >>> kernel_kobj); > >>> @@ -171,7 +450,8 @@ void dma_buf_uninit_sysfs_statistics(void) > >>> int dma_buf_stats_setup(struct dma_buf *dmabuf) > >>> { > >>> struct dma_buf_sysfs_entry *sysfs_entry; > >>> - int ret; > >>> + struct dma_buf_sysfs_entry_metadata *sysfs_metadata; > >>> + struct dmabuf_kobj_work *kobj_work; > >>> > >>> if (!dmabuf || !dmabuf->file) > >>> return -EINVAL; > >>> @@ -188,18 +468,35 @@ int dma_buf_stats_setup(struct dma_buf *dmabuf) > >>> sysfs_entry->kobj.kset =3D dma_buf_per_buffer_stats_kset; > >>> sysfs_entry->dmabuf =3D dmabuf; > >>> > >>> + sysfs_metadata =3D kzalloc(sizeof(struct dma_buf_sysfs_entry_me= tadata), > >>> + GFP_KERNEL); > >>> + if (!sysfs_metadata) { > >>> + kfree(sysfs_entry); > >>> + return -ENOMEM; > >>> + } > >>> + > >>> dmabuf->sysfs_entry =3D sysfs_entry; > >>> > >>> - /* create the directory for buffer stats */ > >>> - ret =3D kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_ktype= , NULL, > >>> - "%lu", file_inode(dmabuf->file)->i_i= no); > >>> - if (ret) > >>> - goto err_sysfs_dmabuf; > >>> + sysfs_metadata->status =3D SYSFS_ENTRY_UNINITIALIZED; > >>> + spin_lock_init(&sysfs_metadata->sysfs_entry_lock); > >>> > >>> - return 0; > >>> + dmabuf->sysfs_entry_metadata =3D sysfs_metadata; > >>> > >>> -err_sysfs_dmabuf: > >>> - kobject_put(&sysfs_entry->kobj); > >>> - dmabuf->sysfs_entry =3D NULL; > >>> - return ret; > >>> + kobj_work =3D kzalloc(sizeof(struct dmabuf_kobj_work), GFP_KERN= EL); > >>> + if (!kobj_work) { > >>> + kfree(sysfs_entry); > >>> + kfree(sysfs_metadata); > >>> + return -ENOMEM; > >>> + } > >>> + > >>> + kobj_work->sysfs_entry =3D dmabuf->sysfs_entry; > >>> + kobj_work->sysfs_metadata =3D dmabuf->sysfs_entry_metadata; > >>> + /* > >>> + * stash the inode number in struct dmabuf_kobj_work since setu= p > >>> + * might race with DMA-BUF teardown. > >>> + */ > >>> + kobj_work->uid =3D file_inode(dmabuf->file)->i_ino; > >>> + > >>> + deferred_kobject_create(kobj_work); > >>> + return 0; > >>> } > >>> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h > >>> index 7ab50076e7a6..0597690023a0 100644 > >>> --- a/include/linux/dma-buf.h > >>> +++ b/include/linux/dma-buf.h > >>> @@ -287,6 +287,50 @@ struct dma_buf_ops { > >>> void (*vunmap)(struct dma_buf *dmabuf, struct dma_buf_map *map= ); > >>> }; > >>> > >>> +#ifdef CONFIG_DMABUF_SYSFS_STATS > >>> +enum sysfs_entry_status { > >>> + SYSFS_ENTRY_UNINITIALIZED, > >>> + SYSFS_ENTRY_INIT_IN_PROGRESS, > >>> + SYSFS_ENTRY_ERROR, > >>> + SYSFS_ENTRY_INIT_ABORTED, > >>> + SYSFS_ENTRY_INITIALIZED, > >>> +}; > >>> + > >>> +/* > >>> + * struct dma_buf_sysfs_entry_metadata - Holds the current status fo= r the > >>> + * DMA-BUF sysfs entry. > >>> + * > >>> + * @status: holds the current status for the DMA-BUF sysfs entry. Th= e status of > >>> + * the sysfs entry has the following path. > >>> + * > >>> + * SYSFS_ENTRY_UNINITIALIZED > >>> + * __________________|____________________ > >>> + * | | > >>> + * SYSFS_ENTRY_INIT_IN_PROGRESS SYSFS_ENTRY_INIT_ABORTED (D= MA-BUF > >>> + * | g= ets freed > >>> + * | b= efore > >>> + * | i= nit) > >>> + * ________|_____________________________________ > >>> + * | | | > >>> + * SYSFS_ENTRY_INITIALIZED | SYSFS_ENTRY_INIT_ABORTED > >>> + * | (DMA-BUF gets freed d= uring kobject > >>> + * | init) > >>> + * | > >>> + * | > >>> + * SYSFS_ENTRY_ERROR > >>> + * (error during kobject init) > >>> + * > >>> + * @sysfs_entry_lock: protects access to @status. > >>> + */ > >>> +struct dma_buf_sysfs_entry_metadata { > >>> + enum sysfs_entry_status status; > >>> + /* > >>> + * Protects sysfs_entry_metadata->status > >>> + */ > >>> + spinlock_t sysfs_entry_lock; > >>> +}; > >>> +#endif > >>> + > >>> /** > >>> * struct dma_buf - shared buffer object > >>> * > >>> @@ -452,6 +496,8 @@ struct dma_buf { > >>> struct kobject kobj; > >>> struct dma_buf *dmabuf; > >>> } *sysfs_entry; > >>> + > >>> + struct dma_buf_sysfs_entry_metadata *sysfs_entry_metadata; > >>> #endif > >>> }; > >>> >