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nptl: Fix racy pipe closing in tst-cancel{20,21}
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The tst-cancel20 open two pipes and creates a thread which blocks
reading the first pipe.  It then issues a signal to activate the
signal handler which in turn blocks reading the second pipe end.
Finally the cancellation cleanup-up handlers are tested by first
closing the all the pipes ends and issuing a pthread_cancel.
The tst-cancel21 have a similar behavior, but use an extra fork
after the test itself.

The race condition occurs if the cancellation handling acts after the
pipe close: in this case read will return EOF (indicating side-effects)
and thus the cancellation must not act.  However current GLIBC
cancellation behavior acts regardless the syscalls returns with
sid-effects.

This patch adjust the test by moving the pipe closing after the
cancellation handling.  This avoid spurious cancellation if the case
of the race described.

Checked on x86_64 and i386.

	* nptl/tst-cancel20.c (do_one_test): Move the pipe closing after
	pthread_join.
	* nptl/tst-cancel21.c (tf): Likewise.
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Adhemerval Zanella authored and Adhemerval Zanella committed Dec 2, 2015
1 parent 7635a88 commit d0e3ffb
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Showing 3 changed files with 24 additions and 12 deletions.
6 changes: 6 additions & 0 deletions ChangeLog
Original file line number Diff line number Diff line change
@@ -1,3 +1,9 @@
2015-12-02 Adhemerval Zanella <adhemerval.zanella@linaro.org>

* nptl/tst-cancel20.c (do_one_test): Move the pipe closing after
pthread_join.
* nptl/tst-cancel21.c (tf): Likewise.

2015-12-01 H.J. Lu <hongjiu.lu@intel.com>

[BZ #19313]
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15 changes: 9 additions & 6 deletions nptl/tst-cancel20.c
Original file line number Diff line number Diff line change
Expand Up @@ -145,12 +145,6 @@ do_one_test (void)
return 1;
}

/* This will cause the read in the child to return. */
close (fd[0]);
close (fd[1]);
close (fd[2]);
close (fd[3]);

void *ret;
if (pthread_join (th, &ret) != 0)
{
Expand All @@ -170,6 +164,15 @@ do_one_test (void)
return 1;
}

/* The pipe closing must be issued after the cancellation handling to avoid
a race condition where the cancellation runs after both pipe ends are
closed. In this case the read syscall returns EOF and the cancellation
must not act. */
close (fd[0]);
close (fd[1]);
close (fd[2]);
close (fd[3]);

return 0;
}

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15 changes: 9 additions & 6 deletions nptl/tst-cancel21.c
Original file line number Diff line number Diff line change
Expand Up @@ -123,12 +123,6 @@ tf (void *arg)
exit (1);
}

/* This will cause the read in the initial thread to return. */
close (fd[0]);
close (fd[1]);
close (fd[2]);
close (fd[3]);

void *ret;
if (pthread_join (th, &ret) != 0)
{
Expand All @@ -154,6 +148,15 @@ tf (void *arg)
exit (1);
}

/* The pipe closing must be issued after the cancellation handling to avoid
a race condition where the cancellation runs after both pipe ends are
closed. In this case the read syscall returns EOF and the cancellation
must not act. */
close (fd[0]);
close (fd[1]);
close (fd[2]);
close (fd[3]);

exit (0);
}

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