diff options
| author | Neeraj Upadhyay <neeraju@codeaurora.org> | 2019-03-11 17:28:03 +0530 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-05-31 06:43:48 -0700 |
| commit | e8cfc3265cdce02a8c26b734b1b2d6b1368f04ba (patch) | |
| tree | d92a6264b329a8eeca6de41b0f281636171e32f5 /include | |
| parent | f618b46f9d282e5d00b197df60e98dbe8c1d6673 (diff) | |
rcu: Do a single rhp->func read in rcu_head_after_call_rcu()
[ Upstream commit b699cce1604e828f19c39845252626eb78cdf38a ]
The rcu_head_after_call_rcu() function reads the rhp->func pointer twice,
which can result in a false-positive WARN_ON_ONCE() if the callback
were passed to call_rcu() between the two reads. Although racing
rcu_head_after_call_rcu() with call_rcu() is to be a dubious use case
(the return value is not reliable in that case), intermittent and
irreproducible warnings are also quite dubious. This commit therefore
uses a single READ_ONCE() to pick up the value of rhp->func once, then
tests that value twice, thus guaranteeing consistent processing within
rcu_head_after_call_rcu()().
Neverthless, racing rcu_head_after_call_rcu() with call_rcu() is still
a dubious use case.
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
[ paulmck: Add blank line after declaration per checkpatch.pl. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/rcupdate.h | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 6cdb1db776cf..922bb6848813 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -878,9 +878,11 @@ static inline void rcu_head_init(struct rcu_head *rhp) static inline bool rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) { - if (READ_ONCE(rhp->func) == f) + rcu_callback_t func = READ_ONCE(rhp->func); + + if (func == f) return true; - WARN_ON_ONCE(READ_ONCE(rhp->func) != (rcu_callback_t)~0L); + WARN_ON_ONCE(func != (rcu_callback_t)~0L); return false; } |