net: stmmac: Fix signed/unsigned wreckage
Subsystems (4)
PATCH 1/1 net: stmmac: Fix signed/unsigned wreckage
The recent addition of timestamp correction to compensate the CDC error introduced a subtle signed/unsigned bug in stmmac_get_tx_hwtstamp() while it managed for some obscure reason to avoid that in stmmac_get_rx_hwtstamp().
The issue is:
s64 adjust = 0;
u64 ns;
adjust += -(2 * (NSEC_PER_SEC / priv->plat->clk_ptp_rate));
ns += adjust;works by chance on 64bit, but falls apart on 32bit because the compiler knows that adjust fits into 32bit and then treats the addition as a u64 + u32 resulting in an off by ~2 seconds failure.
The RX variant uses an u64 for adjust and does the adjustment via
ns -= adjust;
because consistency is obviously overrated.
Get rid of the pointless zero initialized adjust variable and do:
ns -= (2 * NSEC_PER_SEC) / priv->plat->clk_ptp_rate;
which is obviously correct and spares the adjust obfuscation. Aside of that it yields a more accurate result because the multiplication takes place before the integer divide truncation and not afterwards.
Stick the calculation into an inline so it can't be accidentaly disimproved. Return an u32 from that inline as the result is guaranteed to fit which lets the compiler optimize the substraction.
--- drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 23 +++++++++------------- 1 file changed, 10 insertions(+), 13 deletions(-)
drivers/net/ethernet/stmicro/stmmac/stmmac_main.c +10 -13
@@ -511,6 +511,14 @@ bool stmmac_eee_init(struct stmmac_privreturn true; } +static inline u32 stmmac_cdc_adjust (struct stmmac_priv *priv) +{ +/* Correct the clk domain crossing(CDC) error */ +if (priv->plat->has_gmac4 && priv->plat->clk_ptp_rate) +return (2 *NSEC_PER_SEC ) / priv->plat->clk_ptp_rate; +return 0 ; +} +/* stmmac_get_tx_hwtstamp - get HW TX timestamps * @priv: driver private structure * @p : descriptor pointer
@@ -524,7 +532,6 @@ static void stmmac_get_tx_hwtstamp(struc {struct skb_shared_hwtstamps shhwtstamp;bool found = false; -s64 adjust =0 ;u64 ns =0 ;if (!priv->hwts_tx_en)
@@ -543,12 +550,7 @@ static void stmmac_get_tx_hwtstamp(struc }if (found) { -/* Correct the clk domain crossing(CDC) error */ -if (priv->plat->has_gmac4 && priv->plat->clk_ptp_rate) { - adjust += -(2 * (NSEC_PER_SEC / - priv->plat->clk_ptp_rate)); - ns += adjust; - } + ns -=stmmac_cdc_adjust (priv);memset (&shhwtstamp,0 ,sizeof (struct skb_shared_hwtstamps )); shhwtstamp.hwtstamp =ns_to_ktime (ns);
@@ -573,7 +575,6 @@ static void stmmac_get_rx_hwtstamp(struc {struct skb_shared_hwtstamps *shhwtstamp =NULL ;struct dma_desc *desc = p; -u64 adjust =0 ;u64 ns =0 ;if (!priv->hwts_rx_en)
@@ -586,11 +587,7 @@ static void stmmac_get_rx_hwtstamp(strucif (stmmac_get_rx_timestamp_status (priv, p, np, priv->adv_ts)) {stmmac_get_timestamp (priv, desc, priv->adv_ts, &ns); -/* Correct the clk domain crossing(CDC) error */ -if (priv->plat->has_gmac4 && priv->plat->clk_ptp_rate) { - adjust +=2 * (NSEC_PER_SEC / priv->plat->clk_ptp_rate); - ns -= adjust; - } + ns -=stmmac_cdc_adjust (priv);netdev_dbg (priv->dev,"get valid RX hw timestamp %llu\n" , ns); shhwtstamp =skb_hwtstamps (skb);
+ BL
Quoted 34 lines · Thomas Gleixner
The recent addition of timestamp correction to compensate the CDC error introduced a subtle signed/unsigned bug in
stmmac_get_tx_hwtstamp()while it managed for some obscure reason to avoid that instmmac_get_rx_hwtstamp().The issue is:
s64 adjust = 0; u64 ns; adjust += -(2 * (NSEC_PER_SEC / priv->plat->clk_ptp_rate)); ns += adjust;works by chance on 64bit, but falls apart on 32bit because the compiler knows that adjust fits into 32bit and then treats the addition as a u64 + u32 resulting in an off by ~2 seconds failure.
The RX variant uses an u64 for adjust and does the adjustment via
ns -= adjust;because consistency is obviously overrated.
Get rid of the pointless zero initialized adjust variable and do:
ns -= (2 * NSEC_PER_SEC) / priv->plat->clk_ptp_rate;which is obviously correct and spares the adjust obfuscation. Aside of that it yields a more accurate result because the multiplication takes place before the integer divide truncation and not afterwards.
Stick the calculation into an inline so it can't be accidentaly disimproved. Return an u32 from that inline as the result is guaranteed to fit which lets the compiler optimize the substraction.
Quoted 5 lines
Fixes 3600be5f58c1 ("net: stmmac: add timestamp correction to rid CDC sync error")Reported-by Benedikt Spranger <[email protected]>Signed-off-by Thomas Gleixner <[email protected]>Tested-by Benedikt Spranger <[email protected]>
Thanks!
From: Thomas Gleixner
Quoted 14 lines
Sent: 15 November 2021 15:21
The recent addition of timestamp correction to compensate the CDC error introduced a subtle signed/unsigned bug in
stmmac_get_tx_hwtstamp()while it managed for some obscure reason to avoid that instmmac_get_rx_hwtstamp().The issue is:
s64 adjust = 0; u64 ns; adjust += -(2 * (NSEC_PER_SEC / priv->plat->clk_ptp_rate)); ns += adjust;
Quoted 3 lines
works by chance on 64bit, but falls apart on 32bit because the compiler knows that adjust fits into 32bit and then treats the addition as a u64 + u32 resulting in an off by ~2 seconds failure.
The problem is earlier.NSEC_PER_SEC and clk_ptp_rate are almost certainly 32bit and unsigned. So you have:
adjust = (s64)((u64)adjust + (u32)-(2 * (NSEC_PER_SEC/...))); David
-
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Quoted 34 lines · Thomas Gleixner
The recent addition of timestamp correction to compensate the CDC error introduced a subtle signed/unsigned bug in
stmmac_get_tx_hwtstamp()while it managed for some obscure reason to avoid that instmmac_get_rx_hwtstamp().The issue is:
s64 adjust = 0; u64 ns; adjust += -(2 * (NSEC_PER_SEC / priv->plat->clk_ptp_rate)); ns += adjust;works by chance on 64bit, but falls apart on 32bit because the compiler knows that adjust fits into 32bit and then treats the addition as a u64 + u32 resulting in an off by ~2 seconds failure.
The RX variant uses an u64 for adjust and does the adjustment via
ns -= adjust;because consistency is obviously overrated.
Get rid of the pointless zero initialized adjust variable and do:
ns -= (2 * NSEC_PER_SEC) / priv->plat->clk_ptp_rate;which is obviously correct and spares the adjust obfuscation. Aside of that it yields a more accurate result because the multiplication takes place before the integer divide truncation and not afterwards.
Stick the calculation into an inline so it can't be accidentaly disimproved. Return an u32 from that inline as the result is guaranteed to fit which lets the compiler optimize the substraction.
Quoted 6 lines
Fixes 3600be5f58c1 ("net: stmmac: add timestamp correction to rid CDC sync error")Reported-by Benedikt Spranger <[email protected]>Signed-off-by Thomas Gleixner <[email protected]>Tested-by Benedikt Spranger <[email protected]>
Thanks for the fix!
This patch was applied to netdev/net.git (master) by Jakub Kicinski <[email protected]>:
Hello:
This patch was applied to netdev/net.git (master)
by Jakub Kicinski <[email protected]>:
Quoted 10 lines · On Mon, 15 Nov 2021 16:21:23 +0100 you wrote:
The recent addition of timestamp correction to compensate the CDC error introduced a subtle signed/unsigned bug in
stmmac_get_tx_hwtstamp()while it managed for some obscure reason to avoid that instmmac_get_rx_hwtstamp().The issue is:
s64 adjust = 0; u64 ns;[...]
Here is the summary with links:
- net: stmmac: Fix signed/unsigned wreckage
https://git.kernel.org/netdev/net/c/3751c3d34cd5
You are awesome, thank you!
Signature · 2 lines
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