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Subject[tip: locking/core] dma-buf: Remove custom seqcount lockdep class key
The following commit has been merged into the locking/core branch of tip:

Commit-ID: 318ce71f3e3ae4108c1665f3860afa8a2a4c9f02
Gitweb: https://git.kernel.org/tip/318ce71f3e3ae4108c1665f3860afa8a2a4c9f02
Author: Ahmed S. Darwish <a.darwish@linutronix.de>
AuthorDate: Mon, 20 Jul 2020 17:55:17 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 29 Jul 2020 16:14:25 +02:00

dma-buf: Remove custom seqcount lockdep class key

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://lkml.kernel.org/r/20200720155530.1173732-12-a.darwish@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 b45f851..15efa0c 100644
--- a/drivers/dma-buf/dma-resv.c
+++ b/drivers/dma-buf/dma-resv.c
@@ -51,12 +51,6 @@
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
@@ -135,9 +129,8 @@ 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 ee50d10..a6538ae 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
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