commit eb4c2382272ae7ae5d81fdfa5b7a6c86146eaaa4 upstream.

The srcu_gp_start() function is called with the srcu_struct structure's
->lock held, but not with the srcu_data structure's ->lock.  This is
problematic because this function accesses and updates the srcu_data
structure's ->srcu_cblist, which is protected by that lock.  Failing to
hold this lock can result in corruption of the SRCU callback lists,
which in turn can result in arbitrarily bad results.

This commit therefore makes srcu_gp_start() acquire the srcu_data
structure's ->lock across the calls to rcu_segcblist_advance() and
rcu_segcblist_accelerate(), thus preventing this corruption.

Reported-by: Bart Van Assche <bvanassche@acm.org>
Reported-by: Christoph Hellwig <hch@infradead.org>
Reported-by: Sebastian Kuzminsky <seb.kuzminsky@gmail.com>
Signed-off-by: Dennis Krein <Dennis.Krein@netapp.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Tested-by: Dennis Krein <Dennis.Krein@netapp.com>
Cc: <stable@vger.kernel.org> # 4.16.x
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This commit adds the SRCU grace-period number to the rcutorture statistics
printout, which allows it to be compared to the rcutorture "Writer stall
state" message.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit also adjusts some whitespace while in the area.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Revert string-breaking %s as requested by Andy Shevchenko. ]

SRCU has long used ->srcu_gp_seq, and now RCU uses ->gp_seq.  This
commit therefore moves the rcutorture_get_gp_data() function from
a ->gpnum / ->completed pair to ->gp_seq.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit adds the address of the first callback to the per-CPU rcutorture
output in order to allow lost wakeups to be more efficiently tracked down.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit updates the header comment of srcu_funnel_gp_start() to
document the fact that srcu_funnel_gp_start() does the work of
srcu_funnel_exp_start(), in some cases by invoking it directly.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit simply changes some copy-pasta call_rcu() instances to
the correct call_srcu().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

The current cleanup_srcu_struct() flushes work, which prevents it
from being invoked from some workqueue contexts, as well as from
atomic (non-blocking) contexts.  This patch therefore introduced a
cleanup_srcu_struct_quiesced(), which can be invoked only after all
activity on the specified srcu_struct has completed.  This restriction
allows cleanup_srcu_struct_quiesced() to be invoked from workqueue
contexts as well as from atomic contexts.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Nitzan Carmi <nitzanc@mellanox.com>
Tested-by: Nicholas Piggin <npiggin@gmail.com>

fixes.2018.02.23a: Miscellaneous fixes
srcu.2018.02.20a: SRCU updates
torture.2018.02.20a: Torture-test updates

RCU's expedited grace periods can participate in out-of-memory deadlocks
due to all available system_wq kthreads being blocked and there not being
memory available to create more.  This commit prevents such deadlocks
by allocating an RCU-specific workqueue_struct at early boot time, and
providing it with a rescuer to ensure forward progress.  This uses the
shiny new init_rescuer() function provided by Tejun (but indirectly).

This commit also causes SRCU to use this new RCU-specific
workqueue_struct.  Note that SRCU's use of workqueues never blocks them
waiting for readers, so this should be safe from a forward-progress
viewpoint.  Note that this moves SRCU from system_power_efficient_wq
to a normal workqueue.  In the unlikely event that this results in
measurable degradation, a separate power-efficient workqueue will be
creates for SRCU.

Reported-by: Prateek Sood <prsood@codeaurora.org>
Reported-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Tejun Heo <tj@kernel.org>