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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jacob Keller <jacob.e.keller@intel.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Andrew Bowers <andrewx.bowers@intel.com>,
        Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
        "Sasha Levin (Microsoft)" <sashal@kernel.org>
Subject: [PATCH 5.0 039/122] i40e: fix i40e_ptp_adjtime when given a negative delta
Date:   Mon,  6 May 2019 16:31:37 +0200
Message-Id: <20190506143058.408004932@linuxfoundation.org>
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[ Upstream commit b3ccbbce1e455b8454d3935eb9ae0a5f18939e24 ]

Commit 0ac30ce43323 ("i40e: fix up 32 bit timespec references",
2017-07-26) claims to be cleaning up references to 32-bit timespecs.

The actual contents of the commit make no sense, as it converts a call
to timespec64_add into timespec64_add_ns. This would seem ok, if (a) the
change was documented in the commit message, and (b) timespec64_add_ns
supported negative numbers.

timespec64_add_ns doesn't work with signed deltas, because the
implementation is based around iter_div_u64_rem. This change resulted in
a regression where i40e_ptp_adjtime would interpret small negative
adjustments as large positive additions, resulting in incorrect
behavior.

This commit doesn't appear to fix anything, is not well explained, and
introduces a bug, so lets just revert it.

Reverts: 0ac30ce43323 ("i40e: fix up 32 bit timespec references", 2017-07-26)
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org>
---
 drivers/net/ethernet/intel/i40e/i40e_ptp.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_ptp.c b/drivers/net/ethernet/intel/i40e/i40e_ptp.c
index 5fb4353c742b..31575c0bb884 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_ptp.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_ptp.c
@@ -146,12 +146,13 @@ static int i40e_ptp_adjfreq(struct ptp_clock_info *ptp, s32 ppb)
 static int i40e_ptp_adjtime(struct ptp_clock_info *ptp, s64 delta)
 {
 	struct i40e_pf *pf = container_of(ptp, struct i40e_pf, ptp_caps);
-	struct timespec64 now;
+	struct timespec64 now, then;
 
+	then = ns_to_timespec64(delta);
 	mutex_lock(&pf->tmreg_lock);
 
 	i40e_ptp_read(pf, &now, NULL);
-	timespec64_add_ns(&now, delta);
+	now = timespec64_add(now, then);
 	i40e_ptp_write(pf, (const struct timespec64 *)&now);
 
 	mutex_unlock(&pf->tmreg_lock);
-- 
2.20.1