selftests: sysctl: Check the sign of a negative jiffies read

proc_int_k2u_conv_kop() returns the sign through *negp and the magnitude
through *u_ptr.  For a negative value it used to convert the
sign-extended int and negate afterwards, so the magnitude came back as a
wrapped 64-bit number.  Nothing noticed, because no test wrote a
negative value to a jiffies sysctl.

Write one to each of the three int converters and require the value to
read back unchanged.  Each value is chosen to convert exactly at every
CONFIG_HZ, so the test does not depend on it:

	converter		write	jiffies stored	reads back
	jiffies			-1	-HZ		-1
	ms_jiffies		-1000	-HZ		-1000
	userhz_jiffies		-100	-HZ		-100

On a kernel without the fix, at CONFIG_HZ=250:

  # int_jiffies: got '-18372957097414713411', want '-1'
  # int_ms_jiffies: got '-18446744069414585320', want '-1000'
  # int_userhz_jiffies: got '-18446742229035144346', want '-100'
  not ok 1 test_int_jiffies_negative

(paths shortened; the runner prints them under /proc/sys/debug/test_sysctl)

Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Reviewed-by: Bradley Morgan <brads@mainlining.org>
Tested-by: Bradley Morgan <brads@mainlining.org>
Signed-off-by: Joel Granados <joel.granados@kernel.org>

0 files changed, 0 insertions, 0 deletions