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signal: Explain local_irq_save() call

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The explicit local_irq_save() in __lock_task_sighand() is needed to avoid
a potential deadlock condition, as noted in a841796f11 (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>
This commit is contained in:
Paul E. McKenney 2014-05-05 08:18:30 -07:00
parent ab74fdfd4e
commit c41247e1d4
1 changed files with 4 additions and 0 deletions
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4
kernel/signal.c
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@ -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);