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 B91F6C4321E for ; Tue, 11 Jan 2022 08:35:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349000AbiAKIfc (ORCPT ); Tue, 11 Jan 2022 03:35:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59954 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348965AbiAKIfY (ORCPT ); Tue, 11 Jan 2022 03:35:24 -0500 Received: from mail-ot1-x32e.google.com (mail-ot1-x32e.google.com [IPv6:2607:f8b0:4864:20::32e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D130DC06173F for ; Tue, 11 Jan 2022 00:35:23 -0800 (PST) Received: by mail-ot1-x32e.google.com with SMTP id i5-20020a05683033e500b0057a369ac614so17765257otu.10 for ; Tue, 11 Jan 2022 00:35:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=vh6WP8Y/DGjWiyIoCbQZfpI6zz91NHyOgJci5sYTOU4=; b=SW5lx7hfSKqtPdm3EyPBp5gfIvUOFIv4YoLmwOXG2whRIBZc2N5dew2MddtQwGxylr Ucn8l17OXHBmBLvmeCcW1LPir7ia/eJfa40INd3so2FaqWkW53lLIzH8hKcoDHe7mZAr NW+Jx2IdHp4G2snwW7SIidPfNtXLhG5BYdu5A= 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=vh6WP8Y/DGjWiyIoCbQZfpI6zz91NHyOgJci5sYTOU4=; b=tjbRHKsLmAnfX07lVb1uAm2p+xsG1QMd6tTvNPO5XuuIBDRY/f0LjOCTS+jKZYeRVh N2P1YWdR4XGThXB0GWVmShXOfe+sTgbzt0oM/SFGHZQYGMSmk8wyfm6+vpuOjtFxYcI0 4qQgOBi9MEkc9D1lFYYQp91SHiGklJITHTBWFkv4ww1Q/vaSB3+x67/2wdvwG7PLxWA+ w4Z4TAg//GQ67+zosJFvvJr/BSvZOVcdbXYn0l7UZk324E+0NXIeo1gn0DFC3iWjHREB EGCV/Z15fOfU03CtJQWLIcbfsmDYjlaPWaR7JQCHR5rYK8gJEj0aFe0EuXQPqLWiZ1bB CtkQ== X-Gm-Message-State: AOAM532m3coSkSwDb1D5EjvxxmoBzFBwVNGQ2WZu1yXJnD5noqQWKPTd lpspwnymeRlcT10bMLvbKfLuDSYMJoOnMbc2vK6DF6V68aI= X-Google-Smtp-Source: ABdhPJzSmLmCuX/KzZFpk3r3Sf8nuzFBtbikDbOYhTlA9KhMxn23X/ciW5SDc53DCAlONrOXsu70ueux0J8/6puJ9qQ= X-Received: by 2002:a9d:6e0a:: with SMTP id e10mr2581449otr.323.1641890123009; Tue, 11 Jan 2022 00:35:23 -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> <5a6bd742-10ca-2e88-afaa-3744731c2c0c@amd.com> In-Reply-To: From: Daniel Vetter Date: Tue, 11 Jan 2022 09:35:11 +0100 Message-ID: Subject: Re: [PATCH] dma-buf: Move sysfs work out of DMA-BUF export/release path To: Hridya Valsaraju Cc: =?UTF-8?Q?Christian_K=C3=B6nig?= , Sumit Semwal , 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 Tue, Jan 11, 2022 at 7:02 AM Hridya Valsaraju wrote: > > On Sun, Jan 9, 2022 at 11:28 PM Christian K=C3=B6nig > wrote: > > > > Am 07.01.22 um 22:25 schrieb Hridya Valsaraju: > > > On Fri, Jan 7, 2022 at 10:17 AM Hridya Valsaraju = wrote: > > >> 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 r= eclaim > > >>>>>> while holding the kernfs rw semaphore for sysfs in write(exclusi= ve) > > >>>>>> mode. This caused processes who were doing DMA-BUF exports and r= eleases > > >>>>>> to go into uninterruptible sleep since they needed to acquire th= e same > > >>>>>> semaphore for the DMA-BUF sysfs entry creation/deletion. In orde= r to avoid > > >>>>>> blocking DMA-BUF export/release for an indeterminate amount of t= ime > > >>>>>> while another process is holding the sysfs rw semaphore in exclu= sive > > >>>>>> mode, this patch moves the per-buffer sysfs file creation/delete= ion to > > >>>>>> 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 ope= ration > > >>>>> which should be done exactly once in the lifecycle for the most c= ommon > > >>>>> use case. > > >>>>> > > >>>>> Please explain further why that should be necessary. > > >>>> Hi Christian, > > >>>> > > >>>> We noticed that the issue sometimes causes the exporting process t= o go > > >>>> to the uninterrupted sleep state for tens of milliseconds which > > >>>> unfortunately leads to user-perceptible UI jank. This is the reaso= n > > >>>> why we are trying to move the sysfs entry creation and deletion ou= t 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 durin= g > > >> app launches and exits) when there are several DMA-BUFs being export= ed > > >> 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. > > > > Well, that sounds at least better than before. > > > > >> > > >> Regards, > > >> Hridya > > >> > > >>> So this strongly looks like you are trying to optimize for an use c= ase > > >>> where we should probably rethink what userspace is doing here inste= ad. > > > Hello Christian, > > > > > > If you don't mind, could you please elaborate on the above statement? > > > > The purpose of DMA-buf is to share a rather low number of buffers > > between different drivers and/or applications. > > > > For example with triple buffering we have three buffers shared between > > the camera driver and the display driver, same thing for use cases > > between rendering and display. > > > > So even when you have ~100 applications open your should not share more > > than ~300 DMA-buf handles and doing that should absolutely not cause an= y > > problems like you described above. > > > > Long story short when this affects your user experience then your user > > space is exporting *much* more buffers than expected. Especially since > > the sysfs overhead is completely negligible compared to the overhead > > drivers have when they export buffers. > > > > I do not think we can solve this issue from userspace since the > problem is not due to the overhead of sysfs creation/teardown itself. > The problem is that the duration of time for which the exporting > process would need to sleep waiting for the kernfs_rwsem semaphore is > undefined when the holder of the semaphore goes under direct reclaim. > Fsnotify events for sysfs files are also generated while holding the > same semaphore. > > This is also not a problem due to the high number of DMA-BUF > exports during launch time, as even a single export can be delayed for > an unpredictable amount of time. We cannot eliminate DMA-BUF exports > completely during app-launches and we are unfortunately seeing reports > of the exporting process occasionally sleeping long enough to cause > user-visible jankiness :( > > We also looked at whether any optimizations are possible from the > kernfs implementation side[1] but the semaphore is used quite extensively > and it looks like the best way forward would be to remove sysfs > creation/teardown from the DMA-BUF export/release path altogether. We > have some ideas on how we can reduce the code-complexity in the > current patch. If we manage to > simplify it considerably, would the approach of offloading sysfs > creation and teardown into a separate thread be acceptable Christian? > Thank you for the guidance! One worry I have here with doing this async that now userspace might have a dma-buf, but the sysfs entry does not yet exist, or the dma-buf is gone, but the sysfs entry still exists. That's a bit awkward wrt semantics. Also I'm pretty sure that if we can hit this, then other subsystems using kernfs have similar problems, so trying to fix this in kernfs with slightly more fine-grained locking sounds like a much more solid approach. The linked patch talks about how the big delays happen due to direct reclaim, and that might be limited to specific code paths that we need to look at? As-is this feels a bit much like papering over kernfs issues in hackish ways in sysfs users, instead of tackling the problem at its root. -Daniel > Regards, > Hridya > > [1]: https://lore.kernel.org/all/20211118230008.2679780-1-minchan@kernel.= org/ > > > > > > > I think in that light adding sysfs was rather questionable to begin > > with, but that change here is a complete no-go if you ask me. You are > > adding complexity to the kernel for something which should probably be > > optimized in userspace. > > > > Regards, > > Christian. > > > > > Thanks in advance for the guidance! > > > > > > Regards, > > > Hridya > > > > > >>> 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 wou= ld NAK. > > >>> > > >>> Regards, > > >>> Christian. > > >>> > > >>>> Thanks, > > >>>> Hridya > > >>>> > > >>>> > > >>>>> Regards, > > >>>>> Christian. > > >>>>> > > >>>>>> Fixes: bdb8d06dfefd ("dmabuf: Add the capability to expose DMA-B= UF stats 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 sys= fs file being > > >>>>>> + * read and the DMA-BUF being freed by protecting sysfs_entry->= dmabuf. > > >>>>>> + */ > > >>>>>> +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_buf_sysfs_entry, kobj) > > >>>>>> > > >>>>>> /** > > >>>>>> @@ -64,15 +90,26 @@ static ssize_t dma_buf_stats_attribute_show(= struct 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 t= he DMA-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= kobject *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 thr= ead. */ > > >>>>>> +static void dma_buf_sysfs_stats_setup_work(struct dmabuf_kobj_w= ork *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_ktype, 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= _ABORTED) { > > >>>>>> + /* > > >>>>>> + * 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 gets > > >>>>>> + * freed, we know there is no need to tear= down the sysfs > > >>>>>> + * entry. > > >>>>>> + */ > > >>>>>> + sysfs_metadata->status =3D SYSFS_ENTRY_ERR= OR; > > >>>>>> + } > > >>>>>> + 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 init= ialized. > > >>>>>> + */ > > >>>>>> + spin_lock(&sysfs_metadata->sysfs_entry_lock); > > >>>>>> + if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_INIT_IN_PROG= RESS) { > > >>>>>> + sysfs_metadata->status =3D SYSFS_ENTRY_INITIALIZED= ; > > >>>>>> + goto unlock; > > >>>>>> + } > > >>>>>> > > >>>>>> + /* > > >>>>>> + * At this point the status is SYSFS_ENTRY_INIT_ABORTED wh= ich means > > >>>>>> + * that the DMA-BUF has already been freed. Hence, we clea= nup the > > >>>>>> + * sysfs_entry and its metadata since neither of them are = needed > > >>>>>> + * 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 = thread. */ > > >>>>>> +static void dma_buf_sysfs_stats_teardown_work(struct dmabuf_kob= j_work *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= kobject *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_wo= rk) > > >>>>>> { > > >>>>>> + 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_UNINITIALIZE= D) { > > >>>>>> + setup_needed =3D true; > > >>>>>> + sysfs_metadata->status =3D SYSFS_ENTRY_INIT_IN_PRO= GRESS; > > >>>>>> + } else if (sysfs_metadata->status =3D=3D SYSFS_ENTRY_INITI= ALIZED) { > > >>>>>> + teardown_needed =3D true; > > >>>>>> + } > > >>>>>> + > > >>>>>> + /* > > >>>>>> + * It is ok to release the sysfs_entry_lock here. > > >>>>>> + * > > >>>>>> + * If setup_needed is true, we check the status again afte= r 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 e= xpected to the > > >>>>>> + * status. > > >>>>>> + * > > >>>>>> + * If neither setup_needed nor teardown needed are true, i= t > > >>>>>> + * means the DMA-BUF was freed before we got around to set= ting up the > > >>>>>> + * sysfs entry and hence we just need to release the metad= ata and > > >>>>>> + * return. > > >>>>>> + */ > > >>>>>> + spin_unlock(&kobject_work->sysfs_metadata->sysfs_entry_loc= k); > > >>>>>> + > > >>>>>> + 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_wor= k_list, > > >>>>>> + 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_ko= bj_work())); > > >>>>>> + 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, N= ULL, > > >>>>>> + "%s", "dmabuf-kobject-wo= rker"); > > >>>>>> + if (IS_ERR(dmabuf_kobject_task)) { > > >>>>>> + pr_err("Creating thread for deferred sysfs entry c= reation/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 *ko= bject_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_UNINITIALIZE= D || > > >>>>>> + sysfs_metadata->status =3D=3D SYSFS_ENTRY_INIT_IN_PROG= RESS) { > > >>>>>> + /* > > >>>>>> + * The sysfs entry for this buffer has not yet bee= n initialized, > > >>>>>> + * we set the status to SYSFS_ENTRY_INIT_ABORTED t= o abort the > > >>>>>> + * initialization. > > >>>>>> + */ > > >>>>>> + sysfs_metadata->status =3D SYSFS_ENTRY_INIT_ABORTE= D; > > >>>>>> + spin_unlock(&sysfs_metadata->sysfs_entry_lock); > > >>>>>> + > > >>>>>> + /* > > >>>>>> + * In case kobject initialization completes right = as we release > > >>>>>> + * the sysfs_entry_lock, disable show() for the sy= sfs entry by > > >>>>>> + * setting sysfs_entry->dmabuf to NULL to prevent = a race. > > >>>>>> + */ > > >>>>>> + 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 full= y inititalized. > > >>>>>> + * It is ok to release the sysfs_entry_lock here s= ince the > > >>>>>> + * status can no longer change. > > >>>>>> + */ > > >>>>>> + spin_unlock(&sysfs_metadata->sysfs_entry_lock); > > >>>>>> + > > >>>>>> + /* > > >>>>>> + * Meanwhile disable show() for the sysfs entry to= avoid 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_wo= rk), 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_e= ntry; > > >>>>>> + kobj_work->sysfs_metadata =3D dmabuf->sysf= s_entry_metadata; > > >>>>>> + deferred_kobject_create(kobj_work); > > >>>>>> + } > > >>>>>> + > > >>>>>> + return; > > >>>>>> + } > > >>>>>> + > > >>>>>> + /* > > >>>>>> + * status is SYSFS_ENTRY_INIT_ERROR so we only need to fre= e 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_n= o_uevent_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 *dm= abuf) > > >>>>>> 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_ent= ry_metadata), > > >>>>>> + 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_ino); > > >>>>>> - 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= _KERNEL); > > >>>>>> + 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= setup > > >>>>>> + * 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_ma= p *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 stat= us for the > > >>>>>> + * DMA-BUF sysfs entry. > > >>>>>> + * > > >>>>>> + * @status: holds the current status for the DMA-BUF sysfs entr= y. The status of > > >>>>>> + * the sysfs entry has the following path. > > >>>>>> + * > > >>>>>> + * SYSFS_ENTRY_UNINITIALIZED > > >>>>>> + * __________________|____________________ > > >>>>>> + * | | > > >>>>>> + * SYSFS_ENTRY_INIT_IN_PROGRESS SYSFS_ENTRY_INIT_ABORT= ED (DMA-BUF > > >>>>>> + * | = gets freed > > >>>>>> + * | = before > > >>>>>> + * | = init) > > >>>>>> + * ________|_____________________________________ > > >>>>>> + * | | | > > >>>>>> + * SYSFS_ENTRY_INITIALIZED | SYSFS_ENTRY_INIT_ABORTED > > >>>>>> + * | (DMA-BUF gets fr= eed during 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 > > >>>>>> }; > > >>>>>> > > --=20 Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch