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Message-ID: <934ac18c-d53e-beeb-48c1-015a5936e713@amd.com>
Date: Tue, 11 Jan 2022 11:58:07 +0100
From: Christian König <christian.koenig@....com>
To: Daniel Vetter <daniel.vetter@...ll.ch>,
Hridya Valsaraju <hridya@...gle.com>
Cc: Sumit Semwal <sumit.semwal@...aro.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
john.stultz@...aro.org, surenb@...gle.com, kaleshsingh@...gle.com,
tjmercier@...gle.com, keescook@...gle.com
Subject: Re: [PATCH] dma-buf: Move sysfs work out of DMA-BUF export/release
path
Am 11.01.22 um 09:35 schrieb Daniel Vetter:
> On Tue, Jan 11, 2022 at 7:02 AM Hridya Valsaraju <hridya@...gle.com> wrote:
>> On Sun, Jan 9, 2022 at 11:28 PM Christian König
>> <christian.koenig@....com> wrote:
>>> Am 07.01.22 um 22:25 schrieb Hridya Valsaraju:
>>>> On Fri, Jan 7, 2022 at 10:17 AM Hridya Valsaraju <hridya@...gle.com> wrote:
>>>>> On Fri, Jan 7, 2022 at 2:22 AM Christian König <christian.koenig@....com> wrote:
>>>>>> Am 06.01.22 um 20:04 schrieb Hridya Valsaraju:
>>>>>>> On Thu, Jan 6, 2022 at 12:59 AM Christian König
>>>>>>> <christian.koenig@....com> wrote:
>>>>>>>> Am 05.01.22 um 00:51 schrieb Hridya Valsaraju:
>>>>>>>>> Recently, we noticed an issue where a process went into direct reclaim
>>>>>>>>> while holding the kernfs rw semaphore for sysfs in write(exclusive)
>>>>>>>>> mode. This caused processes who were doing DMA-BUF exports and releases
>>>>>>>>> to go into uninterruptible sleep since they needed to acquire the same
>>>>>>>>> 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 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 operation
>>>>>>>> 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.
>>> Well, that sounds at least better than before.
>>>
>>>>> 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.
>>>> 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 any
>>> 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.
Yes, thanks. That's the important information I was looking for.
>> 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?
At bare minimum I suggest to use a work_struct instead of re-inventing
that with kthread.
And then only put the exporting of buffers into the background and not
the teardown.
>> 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.
Which is exactly my feeling as well, yes.
Regards,
Christian.
> -Daniel
>
>> Regards,
>> Hridya
>>
>> [1]: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2F20211118230008.2679780-1-minchan%40kernel.org%2F&data=04%7C01%7Cchristian.koenig%40amd.com%7C261f37c211bc4abe857b08d9d4dd4fd7%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637774869282278924%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=tqWiJAZxpOpk5QrzuisMwt1e9esI1q0npaMHevsQCwI%3D&reserved=0
>>
>>
>>
>>> 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 would NAK.
>>>>>>
>>>>>> Regards,
>>>>>> Christian.
>>>>>>
>>>>>>> Thanks,
>>>>>>> Hridya
>>>>>>>
>>>>>>>
>>>>>>>> Regards,
>>>>>>>> Christian.
>>>>>>>>
>>>>>>>>> Fixes: bdb8d06dfefd ("dmabuf: Add the capability to expose DMA-BUF stats in sysfs")
>>>>>>>>> Signed-off-by: Hridya Valsaraju <hridya@...gle.com>
>>>>>>>>> ---
>>>>>>>>> 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 <linux/dma-buf.h>
>>>>>>>>> #include <linux/dma-resv.h>
>>>>>>>>> +#include <linux/freezer.h>
>>>>>>>>> #include <linux/kobject.h>
>>>>>>>>> +#include <linux/kthread.h>
>>>>>>>>> +#include <linux/list.h>
>>>>>>>>> #include <linux/printk.h>
>>>>>>>>> +#include <linux/sched/signal.h>
>>>>>>>>> #include <linux/slab.h>
>>>>>>>>> #include <linux/sysfs.h>
>>>>>>>>>
>>>>>>>>> #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 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 = to_dma_buf_stats_attr(attr);
>>>>>>>>> sysfs_entry = to_dma_buf_entry_from_kobj(kobj);
>>>>>>>>> +
>>>>>>>>> + /*
>>>>>>>>> + * acquire dmabuf_sysfs_show_lock to prevent a race with the DMA-BUF
>>>>>>>>> + * being freed while sysfs_entry->dmabuf is being accessed.
>>>>>>>>> + */
>>>>>>>>> + spin_lock(&dmabuf_sysfs_show_lock);
>>>>>>>>> dmabuf = 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 = attribute->show(dmabuf, attribute, buf);
>>>>>>>>> + spin_unlock(&dmabuf_sysfs_show_lock);
>>>>>>>>> + return ret;
>>>>>>>>> }
>>>>>>>>>
>>>>>>>>> static const struct sysfs_ops dma_buf_stats_sysfs_ops = {
>>>>>>>>> @@ -118,33 +155,275 @@ static struct kobj_type dma_buf_ktype = {
>>>>>>>>> .default_groups = 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 = dmabuf->sysfs_entry;
>>>>>>>>> - if (!sysfs_entry)
>>>>>>>>> - return;
>>>>>>>>> +static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops = {
>>>>>>>>> + .filter = 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 = kobject_work->sysfs_entry;
>>>>>>>>> + struct dma_buf_sysfs_entry_metadata *sysfs_metadata =
>>>>>>>>> + kobject_work->sysfs_metadata;
>>>>>>>>> + bool free_metadata = false;
>>>>>>>>> +
>>>>>>>>> + int ret = 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 == 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 = 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 teardown the sysfs
>>>>>>>>> + * entry.
>>>>>>>>> + */
>>>>>>>>> + sysfs_metadata->status = 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 initialized.
>>>>>>>>> + */
>>>>>>>>> + spin_lock(&sysfs_metadata->sysfs_entry_lock);
>>>>>>>>> + if (sysfs_metadata->status == SYSFS_ENTRY_INIT_IN_PROGRESS) {
>>>>>>>>> + sysfs_metadata->status = SYSFS_ENTRY_INITIALIZED;
>>>>>>>>> + goto unlock;
>>>>>>>>> + }
>>>>>>>>>
>>>>>>>>> + /*
>>>>>>>>> + * At this point the status is SYSFS_ENTRY_INIT_ABORTED which means
>>>>>>>>> + * that the DMA-BUF has already been freed. Hence, we cleanup the
>>>>>>>>> + * sysfs_entry and its metadata since neither of them are needed
>>>>>>>>> + * anymore.
>>>>>>>>> + */
>>>>>>>>> + free_metadata = 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 = NULL;
>>>>>>>>> + }
>>>>>>>>> }
>>>>>>>>>
>>>>>>>>> +/* teardown of sysfs entries done asynchronously in the worker thread. */
>>>>>>>>> +static void dma_buf_sysfs_stats_teardown_work(struct dmabuf_kobj_work *kobject_work)
>>>>>>>>> +{
>>>>>>>>> + struct dma_buf_sysfs_entry *sysfs_entry = 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 = 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 = false;
>>>>>>>>> + bool teardown_needed = false;
>>>>>>>>> +
>>>>>>>>> + sysfs_metadata = kobject_work->sysfs_metadata;
>>>>>>>>> + spin_lock(&sysfs_metadata->sysfs_entry_lock);
>>>>>>>>> + if (sysfs_metadata->status == SYSFS_ENTRY_UNINITIALIZED) {
>>>>>>>>> + setup_needed = true;
>>>>>>>>> + sysfs_metadata->status = SYSFS_ENTRY_INIT_IN_PROGRESS;
>>>>>>>>> + } else if (sysfs_metadata->status == SYSFS_ENTRY_INITIALIZED) {
>>>>>>>>> + teardown_needed = 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 expected 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 and
>>>>>>>>> + * 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 = list_first_entry_or_null(&dmabuf_kobj_work_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 = get_next_kobj_work()));
>>>>>>>>> + do_kobject_work(kobject_work);
>>>>>>>>> + }
>>>>>>>>> +
>>>>>>>>> return 0;
>>>>>>>>> }
>>>>>>>>>
>>>>>>>>> -static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops = {
>>>>>>>>> - .filter = dmabuf_sysfs_uevent_filter,
>>>>>>>>> -};
>>>>>>>>> +static int kobject_worklist_init(void)
>>>>>>>>> +{
>>>>>>>>> + init_waitqueue_head(&dmabuf_kobject_waitqueue);
>>>>>>>>> + dmabuf_kobject_task = kthread_run(kobject_work_thread, NULL,
>>>>>>>>> + "%s", "dmabuf-kobject-worker");
>>>>>>>>> + if (IS_ERR(dmabuf_kobject_task)) {
>>>>>>>>> + pr_err("Creating thread for deferred sysfs entry creation/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 = dmabuf->sysfs_entry;
>>>>>>>>> + if (!sysfs_entry)
>>>>>>>>> + return;
>>>>>>>>> +
>>>>>>>>> + sysfs_metadata = dmabuf->sysfs_entry_metadata;
>>>>>>>>> + if (!sysfs_metadata)
>>>>>>>>> + return;
>>>>>>>>> +
>>>>>>>>> + spin_lock(&sysfs_metadata->sysfs_entry_lock);
>>>>>>>>> +
>>>>>>>>> + if (sysfs_metadata->status == SYSFS_ENTRY_UNINITIALIZED ||
>>>>>>>>> + sysfs_metadata->status == SYSFS_ENTRY_INIT_IN_PROGRESS) {
>>>>>>>>> + /*
>>>>>>>>> + * The sysfs entry for this buffer has not yet been initialized,
>>>>>>>>> + * we set the status to SYSFS_ENTRY_INIT_ABORTED to abort the
>>>>>>>>> + * initialization.
>>>>>>>>> + */
>>>>>>>>> + sysfs_metadata->status = 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 entry by
>>>>>>>>> + * setting sysfs_entry->dmabuf to NULL to prevent a race.
>>>>>>>>> + */
>>>>>>>>> + spin_lock(&dmabuf_sysfs_show_lock);
>>>>>>>>> + sysfs_entry->dmabuf = NULL;
>>>>>>>>> + spin_unlock(&dmabuf_sysfs_show_lock);
>>>>>>>>> +
>>>>>>>>> + return;
>>>>>>>>> + }
>>>>>>>>> +
>>>>>>>>> + if (sysfs_metadata->status == SYSFS_ENTRY_INITIALIZED) {
>>>>>>>>> + /*
>>>>>>>>> + * queue teardown work only if sysfs_entry is fully inititalized.
>>>>>>>>> + * 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 avoid a race
>>>>>>>>> + * between teardown and show().
>>>>>>>>> + */
>>>>>>>>> + spin_lock(&dmabuf_sysfs_show_lock);
>>>>>>>>> + sysfs_entry->dmabuf = NULL;
>>>>>>>>> + spin_unlock(&dmabuf_sysfs_show_lock);
>>>>>>>>> +
>>>>>>>>> + kobj_work = 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 = dmabuf->sysfs_entry;
>>>>>>>>> + kobj_work->sysfs_metadata = dmabuf->sysfs_entry_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 = 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 = kobject_worklist_init();
>>>>>>>>> + if (ret)
>>>>>>>>> + return ret;
>>>>>>>>> +
>>>>>>>>> dma_buf_stats_kset = kset_create_and_add("dmabuf",
>>>>>>>>> &dmabuf_sysfs_no_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 *dmabuf)
>>>>>>>>> sysfs_entry->kobj.kset = dma_buf_per_buffer_stats_kset;
>>>>>>>>> sysfs_entry->dmabuf = dmabuf;
>>>>>>>>>
>>>>>>>>> + sysfs_metadata = kzalloc(sizeof(struct dma_buf_sysfs_entry_metadata),
>>>>>>>>> + GFP_KERNEL);
>>>>>>>>> + if (!sysfs_metadata) {
>>>>>>>>> + kfree(sysfs_entry);
>>>>>>>>> + return -ENOMEM;
>>>>>>>>> + }
>>>>>>>>> +
>>>>>>>>> dmabuf->sysfs_entry = sysfs_entry;
>>>>>>>>>
>>>>>>>>> - /* create the directory for buffer stats */
>>>>>>>>> - ret = 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 = SYSFS_ENTRY_UNINITIALIZED;
>>>>>>>>> + spin_lock_init(&sysfs_metadata->sysfs_entry_lock);
>>>>>>>>>
>>>>>>>>> - return 0;
>>>>>>>>> + dmabuf->sysfs_entry_metadata = sysfs_metadata;
>>>>>>>>>
>>>>>>>>> -err_sysfs_dmabuf:
>>>>>>>>> - kobject_put(&sysfs_entry->kobj);
>>>>>>>>> - dmabuf->sysfs_entry = NULL;
>>>>>>>>> - return ret;
>>>>>>>>> + kobj_work = kzalloc(sizeof(struct dmabuf_kobj_work), GFP_KERNEL);
>>>>>>>>> + if (!kobj_work) {
>>>>>>>>> + kfree(sysfs_entry);
>>>>>>>>> + kfree(sysfs_metadata);
>>>>>>>>> + return -ENOMEM;
>>>>>>>>> + }
>>>>>>>>> +
>>>>>>>>> + kobj_work->sysfs_entry = dmabuf->sysfs_entry;
>>>>>>>>> + kobj_work->sysfs_metadata = dmabuf->sysfs_entry_metadata;
>>>>>>>>> + /*
>>>>>>>>> + * stash the inode number in struct dmabuf_kobj_work since setup
>>>>>>>>> + * might race with DMA-BUF teardown.
>>>>>>>>> + */
>>>>>>>>> + kobj_work->uid = 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 for the
>>>>>>>>> + * DMA-BUF sysfs entry.
>>>>>>>>> + *
>>>>>>>>> + * @status: holds the current status for the DMA-BUF sysfs entry. The status of
>>>>>>>>> + * the sysfs entry has the following path.
>>>>>>>>> + *
>>>>>>>>> + * SYSFS_ENTRY_UNINITIALIZED
>>>>>>>>> + * __________________|____________________
>>>>>>>>> + * | |
>>>>>>>>> + * SYSFS_ENTRY_INIT_IN_PROGRESS SYSFS_ENTRY_INIT_ABORTED (DMA-BUF
>>>>>>>>> + * | gets freed
>>>>>>>>> + * | before
>>>>>>>>> + * | init)
>>>>>>>>> + * ________|_____________________________________
>>>>>>>>> + * | | |
>>>>>>>>> + * SYSFS_ENTRY_INITIALIZED | SYSFS_ENTRY_INIT_ABORTED
>>>>>>>>> + * | (DMA-BUF gets freed 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
>>>>>>>>> };
>>>>>>>>>
>
>
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