[PATCH v2 0/6] seqlock: seqcount_t call sites bugfixes

[PATCH v2 0/6] seqlock: seqcount_t call sites bugfixes

[Ahmed S. Darwish]

Hi,

Since patch #7 and #8 from the series:

   [PATCH v1 00/25] seqlock: Extend seqcount API with associated locks
   https://lore.kernel.org/lkml/20200519214547.352050-1-a.darwish@linutronix.de

are now pending on the lockdep/x86 IRQ state tracking patch series:

   [PATCH 00/14] x86/entry: disallow #DB more and x86/entry lockdep/nmi
   https://lkml.kernel.org/r/20200529212728.795169701@infradead.org

   [PATCH v3 0/5] lockdep: Change IRQ state tracking to use per-cpu variables
   https://lkml.kernel.org/r/20200529213550.683440625@infradead.org

This is a repost only of the seqcount_t call sites bugfixes that were on
top of the seqlock patch series.

These fixes are independent, and can thus be merged on their own. I'm
reposting them now so they can at least hit -rc2 or -rc3.

Changelog-v2:

  - patch #1: Add a missing up_read() on netdev_get_name() error path
              exit. Thanks to Dan/kbuild-bot report.

  - patch #4: new patch, invalid preemptible context found by the new
              lockdep checks added in the seqlock series + kbuild-bot.

Thanks,

8<--------------

Ahmed S. Darwish (6):
  net: core: device_rename: Use rwsem instead of a seqcount
  net: phy: fixed_phy: Remove unused seqcount
  u64_stats: Document writer non-preemptibility requirement
  net: mdiobus: Disable preemption upon u64_stats update
  block: nr_sects_write(): Disable preemption on seqcount write
  dma-buf: Remove custom seqcount lockdep class key

 block/blk.h                    |  2 ++
 drivers/dma-buf/dma-resv.c     |  9 +------
 drivers/net/phy/fixed_phy.c    | 26 ++++++++------------
 drivers/net/phy/mdio_bus.c     |  2 ++
 include/linux/dma-resv.h       |  2 --
 include/linux/u64_stats_sync.h | 43 ++++++++++++++++++----------------
 net/core/dev.c                 | 40 ++++++++++++++-----------------
 7 files changed, 56 insertions(+), 68 deletions(-)

base-commit: 3d77e6a8804abcc0504c904bd6e5cdf3a5cf8162
--
2.20.1
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[PATCH v2 6/6] dma-buf: Remove custom seqcount lockdep class key

[Ahmed S. Darwish]

Commit 3c3b177a9369 ("reservation: add support for read-only access
using rcu") introduced a sequence counter to manage updates to
reservations. Back then, the reservation object initializer
reservation_object_init() was always inlined.

Having the sequence counter initialization inlined meant that each of
the call sites would have a different lockdep class key, which would've
broken lockdep's deadlock detection. The aforementioned commit thus
introduced, and exported, a custom seqcount lockdep class key and name.

The commit 8735f16803f00 ("dma-buf: cleanup reservation_object_init...")
transformed the reservation object initializer to a normal non-inlined C
function. seqcount_init(), which automatically defines the seqcount
lockdep class key and must be called non-inlined, can now be safely used.

Remove the seqcount custom lockdep class key, name, and export. Use
seqcount_init() inside the dma reservation object initializer.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/dma-buf/dma-resv.c | 9 +--------
 include/linux/dma-resv.h   | 2 --
 2 files changed, 1 insertion(+), 10 deletions(-)

diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
index 4264e64788c4..590ce7ad60a0 100644
--- a/drivers/dma-buf/dma-resv.c
+++ b/drivers/dma-buf/dma-resv.c
@@ -50,12 +50,6 @@
 DEFINE_WD_CLASS(reservation_ww_class);
 EXPORT_SYMBOL(reservation_ww_class);
 
-struct lock_class_key reservation_seqcount_class;
-EXPORT_SYMBOL(reservation_seqcount_class);
-
-const char reservation_seqcount_string[] = "reservation_seqcount";
-EXPORT_SYMBOL(reservation_seqcount_string);
-
 /**
  * dma_resv_list_alloc - allocate fence list
  * @shared_max: number of fences we need space for
@@ -134,9 +128,8 @@ subsys_initcall(dma_resv_lockdep);
 void dma_resv_init(struct dma_resv *obj)
 {
 	ww_mutex_init(&obj->lock, &reservation_ww_class);
+	seqcount_init(&obj->seq);
 
-	__seqcount_init(&obj->seq, reservation_seqcount_string,
-			&reservation_seqcount_class);
 	RCU_INIT_POINTER(obj->fence, NULL);
 	RCU_INIT_POINTER(obj->fence_excl, NULL);
 }
diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
index ee50d10f052b..a6538ae7d93f 100644
--- a/include/linux/dma-resv.h
+++ b/include/linux/dma-resv.h
@@ -46,8 +46,6 @@
 #include <linux/rcupdate.h>
 
 extern struct ww_class reservation_ww_class;
-extern struct lock_class_key reservation_seqcount_class;
-extern const char reservation_seqcount_string[];
 
 /**
  * struct dma_resv_list - a list of shared fences
-- 
2.20.1

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Re: [PATCH v2 0/6] seqlock: seqcount_t call sites bugfixes

[Daniel Vetter]

On Wed, Jun 03, 2020 at 04:49:43PM +0200, Ahmed S. Darwish wrote:
> Hi,
> 
> Since patch #7 and #8 from the series:
> 
>    [PATCH v1 00/25] seqlock: Extend seqcount API with associated locks
>    https://lore.kernel.org/lkml/20200519214547.352050-1-a.darwish@linutronix.de
> 
> are now pending on the lockdep/x86 IRQ state tracking patch series:
> 
>    [PATCH 00/14] x86/entry: disallow #DB more and x86/entry lockdep/nmi
>    https://lkml.kernel.org/r/20200529212728.795169701@infradead.org
> 
>    [PATCH v3 0/5] lockdep: Change IRQ state tracking to use per-cpu variables
>    https://lkml.kernel.org/r/20200529213550.683440625@infradead.org
> 
> This is a repost only of the seqcount_t call sites bugfixes that were on
> top of the seqlock patch series.
> 
> These fixes are independent, and can thus be merged on their own. I'm
> reposting them now so they can at least hit -rc2 or -rc3.

I'm confused on what I should do with patch 6 here for dma-buf. Looks like
just a good cleanup/prep work, so I'd queue it for linux-next and 5.9, but
sounds like you want this in earlier. Do you need this in 5.8-rc for some
work meant for 5.9? Will this go in through some topic branch directly?
Should I apply it?

Patch itself lgtm, I'm just confused what I should do with it.
-Daniel

> 
> Changelog-v2:
> 
>   - patch #1: Add a missing up_read() on netdev_get_name() error path
>               exit. Thanks to Dan/kbuild-bot report.
> 
>   - patch #4: new patch, invalid preemptible context found by the new
>               lockdep checks added in the seqlock series + kbuild-bot.
> 
> Thanks,
> 
> 8<--------------
> 
> Ahmed S. Darwish (6):
>   net: core: device_rename: Use rwsem instead of a seqcount
>   net: phy: fixed_phy: Remove unused seqcount
>   u64_stats: Document writer non-preemptibility requirement
>   net: mdiobus: Disable preemption upon u64_stats update
>   block: nr_sects_write(): Disable preemption on seqcount write
>   dma-buf: Remove custom seqcount lockdep class key
> 
>  block/blk.h                    |  2 ++
>  drivers/dma-buf/dma-resv.c     |  9 +------
>  drivers/net/phy/fixed_phy.c    | 26 ++++++++------------
>  drivers/net/phy/mdio_bus.c     |  2 ++
>  include/linux/dma-resv.h       |  2 --
>  include/linux/u64_stats_sync.h | 43 ++++++++++++++++++----------------
>  net/core/dev.c                 | 40 ++++++++++++++-----------------
>  7 files changed, 56 insertions(+), 68 deletions(-)
> 
> base-commit: 3d77e6a8804abcc0504c904bd6e5cdf3a5cf8162
> --
> 2.20.1

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH v2 0/6] seqlock: seqcount_t call sites bugfixes

[Ahmed S. Darwish]

On Thu, Jun 04, 2020 at 09:28:41AM +0200, Daniel Vetter wrote:
> On Wed, Jun 03, 2020 at 04:49:43PM +0200, Ahmed S. Darwish wrote:
> > Hi,
> >
> > Since patch #7 and #8 from the series:
> >
> >    [PATCH v1 00/25] seqlock: Extend seqcount API with associated locks
> >    https://lore.kernel.org/lkml/20200519214547.352050-1-a.darwish@linutronix.de
> >
> > are now pending on the lockdep/x86 IRQ state tracking patch series:
> >
> >    [PATCH 00/14] x86/entry: disallow #DB more and x86/entry lockdep/nmi
> >    https://lkml.kernel.org/r/20200529212728.795169701@infradead.org
> >
> >    [PATCH v3 0/5] lockdep: Change IRQ state tracking to use per-cpu variables
> >    https://lkml.kernel.org/r/20200529213550.683440625@infradead.org
> >
> > This is a repost only of the seqcount_t call sites bugfixes that were on
> > top of the seqlock patch series.
> >
> > These fixes are independent, and can thus be merged on their own. I'm
> > reposting them now so they can at least hit -rc2 or -rc3.
>
> I'm confused on what I should do with patch 6 here for dma-buf. Looks like
> just a good cleanup/prep work, so I'd queue it for linux-next and 5.9, but
> sounds like you want this in earlier. Do you need this in 5.8-rc for some
> work meant for 5.9? Will this go in through some topic branch directly?
> Should I apply it?
>
> Patch itself lgtm, I'm just confused what I should do with it.
>

My apologies for the confusion. The cover letter is indeed misleading
w.r.t. the dma-buf patch.  It isn't a bugfix, so it shouldn't hit -rc.

Since without this patch compiling the seqcount series will fail, it
will be best to merge it through tip instead.

So all I need for now is a reviewed-by tag :) I will forwoard it to the
tip tree afterwards.

Thanks,

--
Ahmed S. Darwish
Linutronix GmbH
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Re: [PATCH v2 6/6] dma-buf: Remove custom seqcount lockdep class key

[Daniel Vetter]

On Wed, Jun 03, 2020 at 04:49:49PM +0200, Ahmed S. Darwish wrote:
> Commit 3c3b177a9369 ("reservation: add support for read-only access
> using rcu") introduced a sequence counter to manage updates to
> reservations. Back then, the reservation object initializer
> reservation_object_init() was always inlined.
> 
> Having the sequence counter initialization inlined meant that each of
> the call sites would have a different lockdep class key, which would've
> broken lockdep's deadlock detection. The aforementioned commit thus
> introduced, and exported, a custom seqcount lockdep class key and name.
> 
> The commit 8735f16803f00 ("dma-buf: cleanup reservation_object_init...")
> transformed the reservation object initializer to a normal non-inlined C
> function. seqcount_init(), which automatically defines the seqcount
> lockdep class key and must be called non-inlined, can now be safely used.
> 
> Remove the seqcount custom lockdep class key, name, and export. Use
> seqcount_init() inside the dma reservation object initializer.
> 
> Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Patch lgtm, and Ahmed says plan is that this should land through -tip
since it's part of a larger series, so

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>

for merging through whatever tree/branch fits bets. I don't expect
conflicts here, nothing in-flight touching this. I expect this will show
up in 5.9-rc1 or so.

Cheers, Daniel

> ---
>  drivers/dma-buf/dma-resv.c | 9 +--------
>  include/linux/dma-resv.h   | 2 --
>  2 files changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> index 4264e64788c4..590ce7ad60a0 100644
> --- a/drivers/dma-buf/dma-resv.c
> +++ b/drivers/dma-buf/dma-resv.c
> @@ -50,12 +50,6 @@
>  DEFINE_WD_CLASS(reservation_ww_class);
>  EXPORT_SYMBOL(reservation_ww_class);
>  
> -struct lock_class_key reservation_seqcount_class;
> -EXPORT_SYMBOL(reservation_seqcount_class);
> -
> -const char reservation_seqcount_string[] = "reservation_seqcount";
> -EXPORT_SYMBOL(reservation_seqcount_string);
> -
>  /**
>   * dma_resv_list_alloc - allocate fence list
>   * @shared_max: number of fences we need space for
> @@ -134,9 +128,8 @@ subsys_initcall(dma_resv_lockdep);
>  void dma_resv_init(struct dma_resv *obj)
>  {
>  	ww_mutex_init(&obj->lock, &reservation_ww_class);
> +	seqcount_init(&obj->seq);
>  
> -	__seqcount_init(&obj->seq, reservation_seqcount_string,
> -			&reservation_seqcount_class);
>  	RCU_INIT_POINTER(obj->fence, NULL);
>  	RCU_INIT_POINTER(obj->fence_excl, NULL);
>  }
> diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
> index ee50d10f052b..a6538ae7d93f 100644
> --- a/include/linux/dma-resv.h
> +++ b/include/linux/dma-resv.h
> @@ -46,8 +46,6 @@
>  #include <linux/rcupdate.h>
>  
>  extern struct ww_class reservation_ww_class;
> -extern struct lock_class_key reservation_seqcount_class;
> -extern const char reservation_seqcount_string[];
>  
>  /**
>   * struct dma_resv_list - a list of shared fences
> -- 
> 2.20.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH v2 0/6] seqlock: seqcount_t call sites bugfixes

[David Miller]

From: "Ahmed S. Darwish" <a.darwish@linutronix.de>
Date: Wed,  3 Jun 2020 16:49:43 +0200

> Since patch #7 and #8 from the series:
> 
>    [PATCH v1 00/25] seqlock: Extend seqcount API with associated locks
>    https://lore.kernel.org/lkml/20200519214547.352050-1-a.darwish@linutronix.de
> 
> are now pending on the lockdep/x86 IRQ state tracking patch series:
> 
>    [PATCH 00/14] x86/entry: disallow #DB more and x86/entry lockdep/nmi
>    https://lkml.kernel.org/r/20200529212728.795169701@infradead.org
> 
>    [PATCH v3 0/5] lockdep: Change IRQ state tracking to use per-cpu variables
>    https://lkml.kernel.org/r/20200529213550.683440625@infradead.org
> 
> This is a repost only of the seqcount_t call sites bugfixes that were on
> top of the seqlock patch series.
> 
> These fixes are independent, and can thus be merged on their own. I'm
> reposting them now so they can at least hit -rc2 or -rc3.
> 
> Changelog-v2:
> 
>   - patch #1: Add a missing up_read() on netdev_get_name() error path
>               exit. Thanks to Dan/kbuild-bot report.
> 
>   - patch #4: new patch, invalid preemptible context found by the new
>               lockdep checks added in the seqlock series + kbuild-bot.

I'll apply patches 1-4 to the net tree.
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