On Mon, Jan 28, 2019 at 08:23:18AM -0800, Paul E. McKenney wrote:
On Mon, Jan 28, 2019 at 10:39:05AM -0500, Sasha Levin wrote:From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> [ Upstream commit 0607ba8403c4cdb253f8c5200ecf654dfb7790cc ] Ever since cdf7abc4610a ("srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context"), it has been permissible to use SRCU read-side critical sections in interrupt context. This allows __call_srcu() to use SRCU read-side critical sections to prevent a new SRCU grace period from ending before the call to either srcu_funnel_gp_start() or srcu_funnel_exp_start completes, thus preventing SRCU grace-period counter overflow during that time. Note that this does not permit removal of the counter-wrap checks in srcu_gp_end(). These check are necessary to handle the case where a given CPU does not interact at all with SRCU for an extended time period. This commit therefore adds an SRCU read-side critical section to __call_srcu() in order to prevent grace period counter wrap during the funnel-locking process. Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>Hello, Sasha, I recommend -against- backporting this one. It is a theoretical bug that requires rather long preemption, so the risk of backporting likely greatly exceeeds the risk of the bug actually happening, especially on 64-bit systems.
I'll drop it, thanks Paul! -- Thanks, Sasha
