[tip: core/rcu] srcu: Take early exit on memory-allocation failure

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     50edb988534c621a56ca103c0c16ac59e7399f01
Gitweb:        https://git.kernel.org/tip/50edb988534c621a56ca103c0c16ac59e7399f01
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Thu, 10 Sep 2020 11:54:42 -07:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Thu, 19 Nov 2020 19:37:17 -08:00

srcu: Take early exit on memory-allocation failure

It turns out that init_srcu_struct() can be invoked from usermode tasks,
and that fatal signals received by these tasks can cause memory-allocation
failures.  These failures are not handled well by init_srcu_struct(),
so much so that NULL pointer dereferences can result.  This commit
therefore causes init_srcu_struct() to take an early exit upon detection
of memory-allocation failure.

Link: https://lore.kernel.org/lkml/20200908144306.33355-1-aik@xxxxxxxxx/
Reported-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
Tested-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/srcutree.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index c13348e..6f7880a 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -177,11 +177,13 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
 	INIT_DELAYED_WORK(&ssp->work, process_srcu);
 	if (!is_static)
 		ssp->sda = alloc_percpu(struct srcu_data);
+	if (!ssp->sda)
+		return -ENOMEM;
 	init_srcu_struct_nodes(ssp, is_static);
 	ssp->srcu_gp_seq_needed_exp = 0;
 	ssp->srcu_last_gp_end = ktime_get_mono_fast_ns();
 	smp_store_release(&ssp->srcu_gp_seq_needed, 0); /* Init done. */
-	return ssp->sda ? 0 : -ENOMEM;
+	return 0;
 }
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC