From: Geert Uytterhoeven <geert@linux-m68k.org>
To: John Stultz <john.stultz@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Stephen Boyd <sboyd@codeaurora.org>,
"H . Peter Anvin" <hpa@zytor.com>
Cc: Alexander Steffen <Alexander.Steffen@infineon.com>,
Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
Peter Huewe <peterhuewe@gmx.de>,
Jason Gunthorpe <jgunthorpe@obsidianresearch.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org,
Geert Uytterhoeven <geert@linux-m68k.org>
Subject: [PATCH] [RFC] time: Make sure jiffies_to_msecs() preserves non-zero time periods
Date: Tue, 14 Nov 2017 18:36:26 +0100 [thread overview]
Message-ID: <1510680986-29391-1-git-send-email-geert@linux-m68k.org> (raw)
For the common cases where 1000 is a multiple of HZ, or HZ is a multiple
of 1000, jiffies_to_msecs() never returns zero when passed a non-zero
time period.
However, if HZ > 1000 and not an integer multiple of 1000 (e.g. 2001),
jiffies_to_msecs() may return zero for small non-zero time periods.
This may break code that relies on receiving back a non-zero value, e.g.
drivers/char/tpm/tpm2-cmd.c:tpm2_do_selftest().
jiffies_to_usecs() does not need such a fix, as <linux/jiffies.h> does
not support values of HZ larger than 12287, thus rejecting any
problematic huge values of HZ.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
I noticed this issue due to the following compiler warning with
gcc-4.1.2:
drivers/char/tpm/tpm2-cmd.c: In function ‘tpm2_do_selftest’:
drivers/char/tpm/tpm2-cmd.c:851: warning: ‘rc’ may be used uninitialized in this function
With the fix above, this becomes a false positive.
Nevertheless, it may be a good idea to preinitialize rc anyway, but I
have no idea what's the correct value (else I would have sent a patch
to do so ;-).
Fixes: 87434f58be31a96d ("tpm: Use dynamic delay to wait for TPM 2.0 self test result")
---
kernel/time/time.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/time/time.c b/kernel/time/time.c
index bd4e6c7dd6899d83..69b901a8739aad5e 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -314,9 +314,10 @@ unsigned int jiffies_to_msecs(const unsigned long j)
return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
#else
# if BITS_PER_LONG == 32
- return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
+ return (HZ_TO_MSEC_MUL32 * j + (1ULL << HZ_TO_MSEC_SHR32) - 1) >>
+ HZ_TO_MSEC_SHR32;
# else
- return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
+ return (j * HZ_TO_MSEC_NUM + HZ_TO_MSEC_DEN - 1) / HZ_TO_MSEC_DEN;
# endif
#endif
}
--
2.7.4
next reply other threads:[~2017-11-14 17:36 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-14 17:36 Geert Uytterhoeven [this message]
2017-11-14 20:18 ` [PATCH] [RFC] time: Make sure jiffies_to_msecs() preserves non-zero time periods Arnd Bergmann
2017-11-14 20:24 ` Geert Uytterhoeven
2017-11-20 18:51 ` Jarkko Sakkinen
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