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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-05-05 08:18:30 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-07-09 09:14:33 -0700
commitc41247e1d4864c863ee25e029dd53acdb2abc000 (patch)
tree86011181ada393aadad02a79085678bda508d2cc /kernel/signal.c
parentab74fdfd4e11ec040f21cf87edc14fc9f62cc934 (diff)
downloadlwn-c41247e1d4864c863ee25e029dd53acdb2abc000.tar.gz
lwn-c41247e1d4864c863ee25e029dd53acdb2abc000.zip
signal: Explain local_irq_save() call
The explicit local_irq_save() in __lock_task_sighand() is needed to avoid a potential deadlock condition, as noted in a841796f11c90d53 (signal: align __lock_task_sighand() irq disabling and RCU). However, someone reading the code might be forgiven for concluding that this separate local_irq_save() was completely unnecessary. This commit therefore adds a comment referencing the shiny new block comment on rcu_read_unlock(). Reported-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Oleg Nesterov <oleg@redhat.com> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Diffstat (limited to 'kernel/signal.c')
-rw-r--r--kernel/signal.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/kernel/signal.c b/kernel/signal.c
index a4077e90f19f..40b76e351e64 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1263,6 +1263,10 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
struct sighand_struct *sighand;
for (;;) {
+ /*
+ * Disable interrupts early to avoid deadlocks.
+ * See rcu_read_unlock() comment header for details.
+ */
local_irq_save(*flags);
rcu_read_lock();
sighand = rcu_dereference(tsk->sighand);