Commit 12eaaf30 authored Apr 30, 2013 by Oleg Nesterov Committed by Linus Torvalds Apr 30, 2013

set_task_comm: kill the pointless memset() + wmb()



set_task_comm() does memset() + wmb() before strlcpy().  This buys
nothing and to add to the confusion, the comment is wrong.

- We do not need memset() to be "safe from non-terminating string
  reads", the final char is always zero and we never change it.

- wmb() is paired with nothing, it cannot prevent from printing
  the mixture of the old/new data unless the reader takes the lock.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 830e0fc9

fs/exec.c

+0 −10

Original line number	Diff line number	Diff line
		@@ -1027,17 +1027,7 @@ EXPORT_SYMBOL_GPL(get_task_comm);
		void set_task_comm(struct task_struct tsk, char buf)
		{
		task_lock(tsk);

		trace_task_rename(tsk, buf);

		/*
		* Threads may access current->comm without holding
		* the task lock, so write the string carefully.
		* Readers without a lock may see incomplete new
		* names but are safe from non-terminating string reads.
		*/
		memset(tsk->comm, 0, TASK_COMM_LEN);
		wmb();
		strlcpy(tsk->comm, buf, sizeof(tsk->comm));
		task_unlock(tsk);
		perf_event_comm(tsk);