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signal: Document the RCU protection of ->sighand

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__cleanup_sighand() frees sighand without RCU grace period. This is
correct but this looks "obviously buggy" and constantly confuses the
readers, add the comments to explain how this works.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
This commit is contained in:
Oleg Nesterov
2014-09-28 23:44:18 +02:00
committed by Paul E. McKenney
parent eca1a08986
commit 392809b258
2 changed files with 15 additions and 2 deletions
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5
kernel/fork.c
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@@ -1022,11 +1022,14 @@ void __cleanup_sighand(struct sighand_struct *sighand)
{
if (atomic_dec_and_test(&sighand->count)) {
signalfd_cleanup(sighand);
/*
* sighand_cachep is SLAB_DESTROY_BY_RCU so we can free it
* without an RCU grace period, see __lock_task_sighand().
*/
kmem_cache_free(sighand_cachep, sighand);
}
}
/*
* Initialize POSIX timer handling for a thread group.
*/