| Message ID | 1546318276-18993-3-git-send-email-yong.wu@mediatek.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Clean up "mediatek,larb" after adding device_link | expand |
On Mon, Dec 31, 2018 at 8:52 PM Yong Wu <yong.wu@mediatek.com> wrote: > > DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link > automatically on consumer/supplier driver unbind", that means we should > remove whole the device_link when there is no this driver no matter what > the ref_count of the link is. > > CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Signed-off-by: Yong Wu <yong.wu@mediatek.com> > --- > The ref_count of our device_link normally is over 1. When the consumer > device driver is removed, whole the device_link should be removed. > Thus, I add this patch. > --- I will admit to reading about device links for the first time while reviewing this patch, but I don't really get this. Why use a kref at all if we're just going to ignore its value? For instance, I see that if you call device_link_add() with the same supplier and consumer, it uses the kref to return the same link. That machinery is broken with your change. Although I don't see any uses of it, you might also expect a supplier or consumer could do a kref_get() on the link it got back from device_link_add(), and have a reasonable expectation that the link wouldn't be freed out from under it. This would also be broken. Can you explain why your device_links normally have a reference count >1, and why those additional references can't be cleaned up in an orderly fashion? (To be honest, I don't really understand the case for the AUTOREMOVE flags at all. Is there some case where the party that set up the link can't tear it down? Or is this a way to devm_ify the link, where devm itself doesn't work because the links themselves stall out that mechanism?)
On Mon, 2019-02-25 at 15:53 -0800, Evan Green wrote: > On Mon, Dec 31, 2018 at 8:52 PM Yong Wu <yong.wu@mediatek.com> wrote: > > > > DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link > > automatically on consumer/supplier driver unbind", that means we should > > remove whole the device_link when there is no this driver no matter what > > the ref_count of the link is. > > > > CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > > Signed-off-by: Yong Wu <yong.wu@mediatek.com> > > --- > > The ref_count of our device_link normally is over 1. When the consumer > > device driver is removed, whole the device_link should be removed. > > Thus, I add this patch. > > --- > > I will admit to reading about device links for the first time while > reviewing this patch, but I don't really get this. Why use a kref at > all if we're just going to ignore its value? For instance, I see that > if you call device_link_add() with the same supplier and consumer, it > uses the kref to return the same link. That machinery is broken with > your change. Although I don't see any uses of it, you might also > expect a supplier or consumer could do a kref_get() on the link it got > back from device_link_add(), and have a reasonable expectation that > the link wouldn't be freed out from under it. This would also be > broken. > > Can you explain why your device_links normally have a reference count > >1, I use device link between the smi-larb device and the iommu-consumer device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this patchset, we use device_link to link the VDEC device and the smi-larb1 device in the function(mtk_iommu_config). since there are 4 ports, it will call device_link_add 4 times. > > and why those additional references can't be cleaned up in an > orderly fashion? If the iommu-consume device(like VDEC above) is removed, It should enter device_links_driver_cleanup which only ref_put one time. I guess whole the link should be removed at that time. > > (To be honest, I don't really understand the case for the AUTOREMOVE > flags at all. Is there some case where the party that set up the link > can't tear it down? Or is this a way to devm_ify the link, where devm > itself doesn't work because the links themselves stall out that > mechanism?)
On Wed, Feb 27, 2019 at 6:33 AM Yong Wu <yong.wu@mediatek.com> wrote: > > On Mon, 2019-02-25 at 15:53 -0800, Evan Green wrote: > > On Mon, Dec 31, 2018 at 8:52 PM Yong Wu <yong.wu@mediatek.com> wrote: > > > > > > DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link > > > automatically on consumer/supplier driver unbind", that means we should > > > remove whole the device_link when there is no this driver no matter what > > > the ref_count of the link is. > > > > > > CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > > > Signed-off-by: Yong Wu <yong.wu@mediatek.com> > > > --- > > > The ref_count of our device_link normally is over 1. When the consumer > > > device driver is removed, whole the device_link should be removed. > > > Thus, I add this patch. > > > --- > > > > I will admit to reading about device links for the first time while > > reviewing this patch, but I don't really get this. Why use a kref at > > all if we're just going to ignore its value? For instance, I see that > > if you call device_link_add() with the same supplier and consumer, it > > uses the kref to return the same link. That machinery is broken with > > your change. Although I don't see any uses of it, you might also > > expect a supplier or consumer could do a kref_get() on the link it got > > back from device_link_add(), and have a reasonable expectation that > > the link wouldn't be freed out from under it. This would also be > > broken. > > > > Can you explain why your device_links normally have a reference count > > >1, > > I use device link between the smi-larb device and the iommu-consumer > device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this > patchset, we use device_link to link the VDEC device and the smi-larb1 > device in the function(mtk_iommu_config). since there are 4 ports, it > will call device_link_add 4 times. > > > > > and why those additional references can't be cleaned up in an > > orderly fashion? > > If the iommu-consume device(like VDEC above) is removed, It should enter > device_links_driver_cleanup which only ref_put one time. I guess whole > the link should be removed at that time. It seems like Robin had some suggestions about using mtk_iommu_add_device() rather than the attach_dev() to set the links up, and then track them for removal in the corresponding remove_device() callback. Then you wouldn't need this change, right?
On 05/03/2019 20:03, Evan Green wrote: > On Wed, Feb 27, 2019 at 6:33 AM Yong Wu <yong.wu@mediatek.com> wrote: >> >> On Mon, 2019-02-25 at 15:53 -0800, Evan Green wrote: >>> On Mon, Dec 31, 2018 at 8:52 PM Yong Wu <yong.wu@mediatek.com> wrote: >>>> >>>> DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link >>>> automatically on consumer/supplier driver unbind", that means we should >>>> remove whole the device_link when there is no this driver no matter what >>>> the ref_count of the link is. >>>> >>>> CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org> >>>> Signed-off-by: Yong Wu <yong.wu@mediatek.com> >>>> --- >>>> The ref_count of our device_link normally is over 1. When the consumer >>>> device driver is removed, whole the device_link should be removed. >>>> Thus, I add this patch. >>>> --- >>> >>> I will admit to reading about device links for the first time while >>> reviewing this patch, but I don't really get this. Why use a kref at >>> all if we're just going to ignore its value? For instance, I see that >>> if you call device_link_add() with the same supplier and consumer, it >>> uses the kref to return the same link. That machinery is broken with >>> your change. Although I don't see any uses of it, you might also >>> expect a supplier or consumer could do a kref_get() on the link it got >>> back from device_link_add(), and have a reasonable expectation that >>> the link wouldn't be freed out from under it. This would also be >>> broken. >>> >>> Can you explain why your device_links normally have a reference count >>>> 1, >> >> I use device link between the smi-larb device and the iommu-consumer >> device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this >> patchset, we use device_link to link the VDEC device and the smi-larb1 >> device in the function(mtk_iommu_config). since there are 4 ports, it >> will call device_link_add 4 times. >> >>> >>> and why those additional references can't be cleaned up in an >>> orderly fashion? >> >> If the iommu-consume device(like VDEC above) is removed, It should enter >> device_links_driver_cleanup which only ref_put one time. I guess whole >> the link should be removed at that time. > > It seems like Robin had some suggestions about using > mtk_iommu_add_device() rather than the attach_dev() to set the links > up, and then track them for removal in the corresponding > remove_device() callback. Then you wouldn't need this change, right? > FYI, Evan the patch is queued for v5.1-rc1 as 0fe6f7874d46 ("driver core: Remove the link if there is no driver with AUTO flag") So if you think there is something wrong with it, then please provide a fix or raise awareness :)
On Tue, Mar 12, 2019 at 7:21 AM Matthias Brugger <matthias.bgg@gmail.com> wrote: > > > > On 05/03/2019 20:03, Evan Green wrote: > > On Wed, Feb 27, 2019 at 6:33 AM Yong Wu <yong.wu@mediatek.com> wrote: > >> > >> On Mon, 2019-02-25 at 15:53 -0800, Evan Green wrote: > >>> On Mon, Dec 31, 2018 at 8:52 PM Yong Wu <yong.wu@mediatek.com> wrote: > >>>> > >>>> DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link > >>>> automatically on consumer/supplier driver unbind", that means we should > >>>> remove whole the device_link when there is no this driver no matter what > >>>> the ref_count of the link is. > >>>> > >>>> CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > >>>> Signed-off-by: Yong Wu <yong.wu@mediatek.com> > >>>> --- > >>>> The ref_count of our device_link normally is over 1. When the consumer > >>>> device driver is removed, whole the device_link should be removed. > >>>> Thus, I add this patch. > >>>> --- > >>> > >>> I will admit to reading about device links for the first time while > >>> reviewing this patch, but I don't really get this. Why use a kref at > >>> all if we're just going to ignore its value? For instance, I see that > >>> if you call device_link_add() with the same supplier and consumer, it > >>> uses the kref to return the same link. That machinery is broken with > >>> your change. Although I don't see any uses of it, you might also > >>> expect a supplier or consumer could do a kref_get() on the link it got > >>> back from device_link_add(), and have a reasonable expectation that > >>> the link wouldn't be freed out from under it. This would also be > >>> broken. > >>> > >>> Can you explain why your device_links normally have a reference count > >>>> 1, > >> > >> I use device link between the smi-larb device and the iommu-consumer > >> device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this > >> patchset, we use device_link to link the VDEC device and the smi-larb1 > >> device in the function(mtk_iommu_config). since there are 4 ports, it > >> will call device_link_add 4 times. > >> > >>> > >>> and why those additional references can't be cleaned up in an > >>> orderly fashion? > >> > >> If the iommu-consume device(like VDEC above) is removed, It should enter > >> device_links_driver_cleanup which only ref_put one time. I guess whole > >> the link should be removed at that time. > > > > It seems like Robin had some suggestions about using > > mtk_iommu_add_device() rather than the attach_dev() to set the links > > up, and then track them for removal in the corresponding > > remove_device() callback. Then you wouldn't need this change, right? > > > > FYI, Evan the patch is queued for v5.1-rc1 as > 0fe6f7874d46 ("driver core: Remove the link if there is no driver with AUTO flag") > > So if you think there is something wrong with it, then please provide a fix or > raise awareness :) Oh. Thanks for the heads-up Matthias. It's pretty weird that we have the kref there whose count we just completely ignore. I'll try to find some time to submit a patch. -Evan
On Tue, 2019-03-12 at 16:17 -0700, Evan Green wrote: > On Tue, Mar 12, 2019 at 7:21 AM Matthias Brugger <matthias.bgg@gmail.com> wrote: > > > > > > > > On 05/03/2019 20:03, Evan Green wrote: > > > On Wed, Feb 27, 2019 at 6:33 AM Yong Wu <yong.wu@mediatek.com> wrote: > > >> > > >> On Mon, 2019-02-25 at 15:53 -0800, Evan Green wrote: > > >>> On Mon, Dec 31, 2018 at 8:52 PM Yong Wu <yong.wu@mediatek.com> wrote: > > >>>> > > >>>> DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link > > >>>> automatically on consumer/supplier driver unbind", that means we should > > >>>> remove whole the device_link when there is no this driver no matter what > > >>>> the ref_count of the link is. > > >>>> > > >>>> CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > > >>>> Signed-off-by: Yong Wu <yong.wu@mediatek.com> > > >>>> --- > > >>>> The ref_count of our device_link normally is over 1. When the consumer > > >>>> device driver is removed, whole the device_link should be removed. > > >>>> Thus, I add this patch. > > >>>> --- > > >>> > > >>> I will admit to reading about device links for the first time while > > >>> reviewing this patch, but I don't really get this. Why use a kref at > > >>> all if we're just going to ignore its value? For instance, I see that > > >>> if you call device_link_add() with the same supplier and consumer, it > > >>> uses the kref to return the same link. That machinery is broken with > > >>> your change. Although I don't see any uses of it, you might also > > >>> expect a supplier or consumer could do a kref_get() on the link it got > > >>> back from device_link_add(), and have a reasonable expectation that > > >>> the link wouldn't be freed out from under it. This would also be > > >>> broken. > > >>> > > >>> Can you explain why your device_links normally have a reference count > > >>>> 1, > > >> > > >> I use device link between the smi-larb device and the iommu-consumer > > >> device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this > > >> patchset, we use device_link to link the VDEC device and the smi-larb1 > > >> device in the function(mtk_iommu_config). since there are 4 ports, it > > >> will call device_link_add 4 times. > > >> > > >>> > > >>> and why those additional references can't be cleaned up in an > > >>> orderly fashion? > > >> > > >> If the iommu-consume device(like VDEC above) is removed, It should enter > > >> device_links_driver_cleanup which only ref_put one time. I guess whole > > >> the link should be removed at that time. > > > > > > It seems like Robin had some suggestions about using > > > mtk_iommu_add_device() rather than the attach_dev() to set the links > > > up, and then track them for removal in the corresponding > > > remove_device() callback. Then you wouldn't need this change, right? Hi Evan, sorry for reply you so late. I have not got time to try this(Put it in the add_device), But I guess it works. At that time the ref_cnt here should be 1, then this patch is unnecessary. > > > > > > > FYI, Evan the patch is queued for v5.1-rc1 as > > 0fe6f7874d46 ("driver core: Remove the link if there is no driver with AUTO flag") > > > > So if you think there is something wrong with it, then please provide a fix or > > raise awareness :) > > Oh. Thanks for the heads-up Matthias. It's pretty weird that we have > the kref there whose count we just completely ignore. I'll try to find > some time to submit a patch. Thanks very much if you improve this. > -Evan
diff --git a/drivers/base/core.c b/drivers/base/core.c index 04bbcd7..4f3c5bc 100644 --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -511,7 +511,7 @@ static void __device_links_no_driver(struct device *dev) continue; if (link->flags & DL_FLAG_AUTOREMOVE_CONSUMER) - kref_put(&link->kref, __device_link_del); + __device_link_del(&link->kref); else if (link->status != DL_STATE_SUPPLIER_UNBIND) WRITE_ONCE(link->status, DL_STATE_AVAILABLE); } @@ -556,7 +556,7 @@ void device_links_driver_cleanup(struct device *dev) */ if (link->status == DL_STATE_SUPPLIER_UNBIND && link->flags & DL_FLAG_AUTOREMOVE_SUPPLIER) - kref_put(&link->kref, __device_link_del); + __device_link_del(&link->kref); WRITE_ONCE(link->status, DL_STATE_DORMANT); }
DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link automatically on consumer/supplier driver unbind", that means we should remove whole the device_link when there is no this driver no matter what the ref_count of the link is. CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Yong Wu <yong.wu@mediatek.com> --- The ref_count of our device_link normally is over 1. When the consumer device driver is removed, whole the device_link should be removed. Thus, I add this patch. --- drivers/base/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)