ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 95 insertions, 0 deletions

diff --git a/drivers/net/phy/linkmode.c b/drivers/net/phy/linkmode.c
new file mode 100644
index 000000000..f60560fe3
--- /dev/null
+++ b/drivers/net/phy/linkmode.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0+
+#include <linux/linkmode.h>
+
+/**
+ * linkmode_resolve_pause - resolve the allowable pause modes
+ * @local_adv: local advertisement in ethtool format
+ * @partner_adv: partner advertisement in ethtool format
+ * @tx_pause: pointer to bool to indicate whether transmit pause should be
+ * enabled.
+ * @rx_pause: pointer to bool to indicate whether receive pause should be
+ * enabled.
+ *
+ * Flow control is resolved according to our and the link partners
+ * advertisements using the following drawn from the 802.3 specs:
+ *  Local device  Link partner
+ *  Pause AsymDir Pause AsymDir Result
+ *    0     X       0     X     Disabled
+ *    0     1       1     0     Disabled
+ *    0     1       1     1     TX
+ *    1     0       0     X     Disabled
+ *    1     X       1     X     TX+RX
+ *    1     1       0     1     RX
+ */
+void linkmode_resolve_pause(const unsigned long *local_adv,
+			    const unsigned long *partner_adv,
+			    bool *tx_pause, bool *rx_pause)
+{
+	__ETHTOOL_DECLARE_LINK_MODE_MASK(m);
+
+	linkmode_and(m, local_adv, partner_adv);
+	if (linkmode_test_bit(ETHTOOL_LINK_MODE_Pause_BIT, m)) {
+		*tx_pause = true;
+		*rx_pause = true;
+	} else if (linkmode_test_bit(ETHTOOL_LINK_MODE_Asym_Pause_BIT, m)) {
+		*tx_pause = linkmode_test_bit(ETHTOOL_LINK_MODE_Pause_BIT,
+					      partner_adv);
+		*rx_pause = linkmode_test_bit(ETHTOOL_LINK_MODE_Pause_BIT,
+					      local_adv);
+	} else {
+		*tx_pause = false;
+		*rx_pause = false;
+	}
+}
+EXPORT_SYMBOL_GPL(linkmode_resolve_pause);
+
+/**
+ * linkmode_set_pause - set the pause mode advertisement
+ * @advertisement: advertisement in ethtool format
+ * @tx: boolean from ethtool struct ethtool_pauseparam tx_pause member
+ * @rx: boolean from ethtool struct ethtool_pauseparam rx_pause member
+ *
+ * Configure the advertised Pause and Asym_Pause bits according to the
+ * capabilities of provided in @tx and @rx.
+ *
+ * We convert as follows:
+ *  tx rx  Pause AsymDir
+ *  0  0   0     0
+ *  0  1   1     1
+ *  1  0   0     1
+ *  1  1   1     0
+ *
+ * Note: this translation from ethtool tx/rx notation to the advertisement
+ * is actually very problematical. Here are some examples:
+ *
+ * For tx=0 rx=1, meaning transmit is unsupported, receive is supported:
+ *
+ *  Local device  Link partner
+ *  Pause AsymDir Pause AsymDir Result
+ *    1     1       1     0     TX + RX - but we have no TX support.
+ *    1     1       0     1	Only this gives RX only
+ *
+ * For tx=1 rx=1, meaning we have the capability to transmit and receive
+ * pause frames:
+ *
+ *  Local device  Link partner
+ *  Pause AsymDir Pause AsymDir Result
+ *    1     0       0     1     Disabled - but since we do support tx and rx,
+ *				this should resolve to RX only.
+ *
+ * Hence, asking for:
+ *  rx=1 tx=0 gives Pause+AsymDir advertisement, but we may end up
+ *            resolving to tx+rx pause or only rx pause depending on
+ *            the partners advertisement.
+ *  rx=0 tx=1 gives AsymDir only, which will only give tx pause if
+ *            the partners advertisement allows it.
+ *  rx=1 tx=1 gives Pause only, which will only allow tx+rx pause
+ *            if the other end also advertises Pause.
+ */
+void linkmode_set_pause(unsigned long *advertisement, bool tx, bool rx)
+{
+	linkmode_mod_bit(ETHTOOL_LINK_MODE_Pause_BIT, advertisement, rx);
+	linkmode_mod_bit(ETHTOOL_LINK_MODE_Asym_Pause_BIT, advertisement,
+			 rx ^ tx);
+}
+EXPORT_SYMBOL_GPL(linkmode_set_pause);