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dma-buf: Restart reservation_object_get_fences_rcu() after writes

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In order to be completely generic, we have to double check the read
seqlock after acquiring a reference to the fence. If the driver is
allocating fences from a SLAB_DESTROY_BY_RCU, or similar freelist, then
within an RCU grace period a fence may be freed and reallocated. The RCU
read side critical section does not prevent this reallocation, instead
we have to inspect the reservation's seqlock to double check if the
fences have been reassigned as we were acquiring our reference.

Signed-off-by: Chris Wilson <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Christian König <[email protected]>
Cc: Alex Deucher <[email protected]>
Cc: Sumit Semwal <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Reviewed-by: Daniel Vetter <[email protected]>
Signed-off-by: Sumit Semwal <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
This commit is contained in:
Chris Wilson 2016-08-29 08:08:30 +01:00 • committed by Sumit Semwal
commit fedf54132d
1 changed files with 31 additions and 40 deletions
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71
drivers/dma-buf/reservation.c
View file

@ -280,18 +280,24 @@ int reservation_object_get_fences_rcu(struct reservation_object *obj,
unsigned *pshared_count,
struct fence ***pshared)
{
unsigned shared_count = 0;
unsigned retry = 1;
struct fence **shared = NULL, *fence_excl = NULL;
int ret = 0;
struct fence **shared = NULL;
struct fence *fence_excl;
unsigned int shared_count;
int ret = 1;
while (retry) {
do {
struct reservation_object_list *fobj;
unsigned seq;
unsigned int i;
seq = read_seqcount_begin(&obj->seq);
shared_count = i = 0;
rcu_read_lock();
seq = read_seqcount_begin(&obj->seq);
fence_excl = rcu_dereference(obj->fence_excl);
if (fence_excl && !fence_get_rcu(fence_excl))
goto unlock;
fobj = rcu_dereference(obj->fence);
if (fobj) {
@ -309,52 +315,37 @@ int reservation_object_get_fences_rcu(struct reservation_object *obj,
}
ret = -ENOMEM;
shared_count = 0;
break;
}
shared = nshared;
memcpy(shared, fobj->shared, sz);
shared_count = fobj->shared_count;
} else
shared_count = 0;
fence_excl = rcu_dereference(obj->fence_excl);
retry = read_seqcount_retry(&obj->seq, seq);
if (retry)
goto unlock;
if (!fence_excl || fence_get_rcu(fence_excl)) {
unsigned i;
for (i = 0; i < shared_count; ++i) {
if (fence_get_rcu(shared[i]))
continue;
/* uh oh, refcount failed, abort and retry */
while (i--)
fence_put(shared[i]);
if (fence_excl) {
fence_put(fence_excl);
fence_excl = NULL;
}
retry = 1;
break;
shared[i] = rcu_dereference(fobj->shared[i]);
if (!fence_get_rcu(shared[i]))
break;
}
} else
retry = 1;
}
if (i != shared_count || read_seqcount_retry(&obj->seq, seq)) {
while (i--)
fence_put(shared[i]);
fence_put(fence_excl);
goto unlock;
}
ret = 0;
unlock:
rcu_read_unlock();
}
*pshared_count = shared_count;
if (shared_count)
*pshared = shared;
else {
*pshared = NULL;
} while (ret);
if (!shared_count) {
kfree(shared);
shared = NULL;
}
*pshared_count = shared_count;
*pshared = shared;
*pfence_excl = fence_excl;
return ret;