drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c | 94 ++++++++++++++++++--- 1 file changed, 83 insertions(+), 11 deletions(-)
xgbe_phy_sfp_detect() acquires xgbe_phy_comm_lock (via
xgbe_phy_get_comm_ownership()) and holds it across calls that can end
up freeing the external PHY device:
xgbe_phy_sfp_detect()
xgbe_phy_get_comm_ownership() <- mutex_lock
xgbe_phy_sfp_mod_absent() / xgbe_phy_sfp_read_eeprom() (SFP changed)
xgbe_phy_free_phy_device()
phy_detach()
phy_suspend()
genphy_suspend()
xgbe_phy_mii_read_c22() <- mii_bus->read
xgbe_phy_get_comm_ownership() <- mutex_lock again
xgbe_phy_comm_lock is a plain, non-recursive mutex. phy_detach() ends
up calling back into this driver's own MDIO bus callbacks
(xgbe_phy_mii_read_c22()/xgbe_phy_mii_write_c22(), reached via
genphy_suspend() during phy_detach()), which independently acquire the
same lock, so the second acquisition deadlocks the task tearing down
the SFP module.
This is reliably reproducible by removing an SFP module while an
external PHY is attached: the removal handler hangs forever inside
xgbe_phy_free_phy_device(), confirmed via /proc/<pid>/stack and the
kernel hung-task detector (blocked 368s+). Reproduced on a SolidRun
Bedrock V3000 (AMD Ryzen Embedded V3C48).
There were two call paths into xgbe_phy_free_phy_device() while the
mutex was held: the module-absent path, and a second one inside
xgbe_phy_sfp_read_eeprom() when the EEPROM contents change (e.g. a
module swap).
Fix this by never calling xgbe_phy_free_phy_device() (directly, or via
xgbe_phy_sfp_mod_absent()) while holding xgbe_phy_comm_lock.
xgbe_phy_sfp_read_eeprom() no longer frees the PHY device itself; it
only records that the SFP changed. xgbe_phy_sfp_detect() releases the
mutex before calling xgbe_phy_sfp_mod_absent() or
xgbe_phy_free_phy_device(), and re-acquires it only around the
remaining raw I2C access in xgbe_phy_sfp_external_phy(). Neither
xgbe_phy_sfp_mod_absent() nor xgbe_phy_sfp_parse_eeprom()/
xgbe_phy_sfp_phy_settings() touch hardware directly, so they don't
need the mutex held.
phy_detach()/phy_device_remove() additionally require RTNL to be held
by the caller. The callers here run from the service workqueue with no
lock held, and a plain rtnl_lock() cannot be used: xgbe_stopdev()
(system workqueue) takes rtnl_lock() and then calls
flush_workqueue(pdata->dev_workqueue) inside xgbe_stop(), which would
block waiting for this very (dev_workqueue) work item to finish, while
that work item is blocked waiting to reacquire RTNL from
xgbe_stopdev() - an ABBA deadlock. Use a non-blocking rtnl_trylock()
instead: on contention, skip the teardown for this poll and let the
next service poll (100ms-1s later) retry it; if the interface is going
down concurrently, xgbe_phy_stop() (phy_impl.stop) frees the PHY
itself under RTNL already held by its own caller, so nothing is lost
by skipping here.
Taking RTNL around the free also closes a second, independent race:
xgbe does not opt into the newer per-netdevice instance lock
(netdev_need_ops_lock() in include/net/netdev_lock.h checks
dev->request_ops_lock / dev->queue_mgmt_ops / dev->netdev_ops->
net_shaper_ops, none of which this driver sets), so __dev_ethtool()
computes need_rtnl = true and takes rtnl_lock() before calling into
this driver's set_link_ksettings()/set_pauseparam(), which dereference
phy_data->phydev without any lock of their own. Before this change,
xgbe_phy_free_phy_device() could free phy_data->phydev out from under
those ethtool paths with nothing serializing the two. With the free
now gated on rtnl_trylock(), it only proceeds while holding RTNL, so
it is properly excluded from any ethtool_ops call on this device: a
concurrent ethtool call either already holds RTNL (the trylock loses
and the free is retried later) or is blocked waiting to acquire it
(behind the still-held lock from the free side).
Finally, if re-acquiring comm ownership for xgbe_phy_sfp_external_phy()
fails after a new SFP's EEPROM has already been parsed, fall back to
the "no module" state (same as the existing xgbe_phy_sfp_read_eeprom()
failure path) instead of leaving sfp_changed/sfp_eeprom/sfp_base
updated for a module whose sfp_phy_avail was never actually set.
Fixes: abf0a1c2b26a ("amd-xgbe: Add support for SFP+ modules")
Cc: stable@vger.kernel.org
Signed-off-by: Stepan Svatenko <ssvatenko@iit.org.ua>
Assisted-by: Claude Code:claude-sonnet-5 [Bash] [Read] [Edit]
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
---
Changes since v1:
- Use rtnl_trylock() instead of leaving the PHY teardown unguarded,
closing both the ABBA deadlock against xgbe_stopdev()'s
flush_workqueue(pdata->dev_workqueue) under RTNL, and a
use-after-free race against the ethtool_ops paths
(set_link_ksettings()/set_pauseparam()) that dereference
phy_data->phydev without their own locking (both reported in
review).
- Handle the case where re-acquiring comm_ownership after parsing a
new SFP's EEPROM fails, instead of leaving stale/incomplete SFP
state in place (reported in review).
---
drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c | 94 ++++++++++++++++++---
1 file changed, 83 insertions(+), 11 deletions(-)
diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c b/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c
index 59a074ed312a..8c625a0340c4 100644
--- a/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c
+++ b/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c
@@ -11,6 +11,7 @@
#include <linux/mdio.h>
#include <linux/phy.h>
#include <linux/ethtool.h>
+#include <linux/rtnetlink.h>
#include "xgbe.h"
#include "xgbe-common.h"
@@ -1218,7 +1219,13 @@ static int xgbe_phy_sfp_read_eeprom(struct xgbe_prv_data *pdata)
goto put;
}
- /* Check for an added or changed SFP */
+ /* Check for an added or changed SFP. Freeing any existing external
+ * PHY device is deferred to the caller: xgbe_phy_free_phy_device()
+ * can end up calling back into this driver's MDIO read/write
+ * routines (via phy_detach() -> phy_suspend()), which take the
+ * comm ownership mutex themselves, and that mutex is held across
+ * this call.
+ */
if (memcmp(&phy_data->sfp_eeprom, &sfp_eeprom, sizeof(sfp_eeprom))) {
phy_data->sfp_changed = 1;
@@ -1226,8 +1233,6 @@ static int xgbe_phy_sfp_read_eeprom(struct xgbe_prv_data *pdata)
xgbe_phy_sfp_eeprom_info(pdata, &sfp_eeprom);
memcpy(&phy_data->sfp_eeprom, &sfp_eeprom, sizeof(sfp_eeprom));
-
- xgbe_phy_free_phy_device(pdata);
} else {
phy_data->sfp_changed = 0;
}
@@ -1268,9 +1273,47 @@ static void xgbe_phy_sfp_mod_absent(struct xgbe_prv_data *pdata)
phy_data->sfp_mod_absent = 1;
phy_data->sfp_phy_avail = 0;
+ phy_data->sfp_changed = 0;
memset(&phy_data->sfp_eeprom, 0, sizeof(phy_data->sfp_eeprom));
}
+/* phy_detach()/phy_device_remove(), called from xgbe_phy_free_phy_device()
+ * below, require RTNL to be held by the caller (phy_detach() itself uses
+ * rtnl_dereference() and phy_link_topo_del_phy()). The callers below run
+ * from the service workqueue with no lock held, so a plain rtnl_lock()
+ * cannot be used here: xgbe_stopdev() (system workqueue) takes rtnl_lock()
+ * and then calls flush_workqueue(pdata->dev_workqueue) inside xgbe_stop(),
+ * which would block waiting for this very (dev_workqueue) work item to
+ * finish - while it is blocked waiting to reacquire RTNL from
+ * xgbe_stopdev(). That is an ABBA deadlock, the same class of bug this
+ * driver just fixed elsewhere.
+ *
+ * Use a non-blocking rtnl_trylock() instead: on contention, skip the
+ * teardown for this poll and let the next service poll (100ms-1s later)
+ * retry it. If the interface is going down concurrently, xgbe_phy_stop()
+ * (phy_impl.stop) frees the PHY itself, under RTNL already held by its
+ * own caller - so nothing is lost by skipping here.
+ */
+static void xgbe_phy_sfp_mod_absent_safe(struct xgbe_prv_data *pdata)
+{
+ if (!rtnl_trylock())
+ return;
+
+ xgbe_phy_sfp_mod_absent(pdata);
+
+ rtnl_unlock();
+}
+
+static void xgbe_phy_free_phy_device_safe(struct xgbe_prv_data *pdata)
+{
+ if (!rtnl_trylock())
+ return;
+
+ xgbe_phy_free_phy_device(pdata);
+
+ rtnl_unlock();
+}
+
static void xgbe_phy_sfp_reset(struct xgbe_phy_data *phy_data)
{
phy_data->sfp_rx_los = 0;
@@ -1296,26 +1339,55 @@ static void xgbe_phy_sfp_detect(struct xgbe_prv_data *pdata)
/* Read the SFP signals and check for module presence */
xgbe_phy_sfp_signals(pdata);
if (phy_data->sfp_mod_absent) {
- xgbe_phy_sfp_mod_absent(pdata);
- goto put;
+ /* xgbe_phy_sfp_mod_absent() calls xgbe_phy_free_phy_device(),
+ * which can call back into this driver's MDIO read/write
+ * routines via phy_detach() -> phy_suspend(). Those routines
+ * take the comm ownership mutex themselves, so it must be
+ * released before making this call.
+ */
+ xgbe_phy_put_comm_ownership(pdata);
+ xgbe_phy_sfp_mod_absent_safe(pdata);
+ goto settings;
}
ret = xgbe_phy_sfp_read_eeprom(pdata);
+ xgbe_phy_put_comm_ownership(pdata);
if (ret) {
/* Treat any error as if there isn't an SFP plugged in */
xgbe_phy_sfp_reset(phy_data);
- xgbe_phy_sfp_mod_absent(pdata);
- goto put;
+ xgbe_phy_sfp_mod_absent_safe(pdata);
+ goto settings;
}
+ /* Same reasoning as above: this must run without the comm
+ * ownership mutex held.
+ */
+ if (phy_data->sfp_changed)
+ xgbe_phy_free_phy_device_safe(pdata);
+
xgbe_phy_sfp_parse_eeprom(pdata);
- xgbe_phy_sfp_external_phy(pdata);
+ /* Re-acquire ownership for the external PHY access below; it talks
+ * to the SFP over I2C directly and needs the mutex held again.
+ */
+ ret = xgbe_phy_get_comm_ownership(pdata);
+ if (!ret) {
+ xgbe_phy_sfp_external_phy(pdata);
+ xgbe_phy_put_comm_ownership(pdata);
+ } else {
+ /* Could not finish bringing up the new module: sfp_changed,
+ * sfp_eeprom and sfp_base/sfp_speed were already updated
+ * above for it, but external_phy() (and thus sfp_phy_avail)
+ * never ran. Fall back to "no module" state instead of
+ * committing to a half-initialized one - same pattern as
+ * the read_eeprom() failure path above.
+ */
+ xgbe_phy_sfp_reset(phy_data);
+ xgbe_phy_sfp_mod_absent_safe(pdata);
+ }
-put:
+settings:
xgbe_phy_sfp_phy_settings(pdata);
-
- xgbe_phy_put_comm_ownership(pdata);
}
static int xgbe_phy_module_eeprom(struct xgbe_prv_data *pdata,
--
2.55.0Thank you for your contribution! Sashiko AI review found 3 potential
issue(s) to consider.
Critical: 0 · High: 3 · Medium: 0 · Low: 0
If you believe none of the issues are legitimate, please reply to each
issue of Medium severity or higher and explain why the AI is wrong.
If any of them are legitimate and you plan to respin, please let patchwork
know by including "pw-bot: cr" as a separate line at the end of your reply
(one such reply per series is enough).
- [High] The deferred external-PHY teardown introduced by this patch is
silently and permanently lost when rtnl_trylock() fails.
- [High] The documented precondition that justifies rtnl_trylock() is
factually wrong.
- [High] xgbe_phy_sfp_mod_absent_safe() (xgbe-phy-v2.c:1297-1305) skips
the whole module-absent bookkeeping when rtnl_trylock() fails, yet…
--
amd-xgbe: fix comm_ownership mutex deadlock on SFP module removal
This moves the external PHY teardown out from under xgbe_phy_comm_lock so
that phy_detach() can no longer re-enter the driver's MDIO callbacks and
deadlock on the same non-recursive mutex. The teardown is now done from
two new helpers that take RTNL with rtnl_trylock() before calling
xgbe_phy_sfp_mod_absent() / xgbe_phy_free_phy_device().
A few questions about the new trylock-based teardown below.
> diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c b/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c
> index 59a074ed312a..8c625a0340c4 100644
> --- a/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c
> +++ b/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c
[ ... ]
> @@ -1218,7 +1219,13 @@ static int xgbe_phy_sfp_read_eeprom(struct xgbe_prv_data *pdata)
> goto put;
> }
>
> - /* Check for an added or changed SFP */
> + /* Check for an added or changed SFP. Freeing any existing external
> + * PHY device is deferred to the caller: xgbe_phy_free_phy_device()
> + * can end up calling back into this driver's MDIO read/write
> + * routines (via phy_detach() -> phy_suspend()), which take the
> + * comm ownership mutex themselves, and that mutex is held across
> + * this call.
> + */
> if (memcmp(&phy_data->sfp_eeprom, &sfp_eeprom, sizeof(sfp_eeprom))) {
> phy_data->sfp_changed = 1;
>
> @@ -1226,8 +1233,6 @@ static int xgbe_phy_sfp_read_eeprom(struct xgbe_prv_data *pdata)
> xgbe_phy_sfp_eeprom_info(pdata, &sfp_eeprom);
>
> memcpy(&phy_data->sfp_eeprom, &sfp_eeprom, sizeof(sfp_eeprom));
> -
> - xgbe_phy_free_phy_device(pdata);
> } else {
> phy_data->sfp_changed = 0;
> }
Note for the comment below: this memcpy() commits the new module's EEPROM
into phy_data->sfp_eeprom in the very same pass that sets sfp_changed = 1,
so the "changed" condition is consumed here and cannot be re-derived on a
later poll.
> @@ -1268,9 +1273,47 @@ static void xgbe_phy_sfp_mod_absent(struct xgbe_prv_data *pdata)
>
> phy_data->sfp_mod_absent = 1;
> phy_data->sfp_phy_avail = 0;
> + phy_data->sfp_changed = 0;
> memset(&phy_data->sfp_eeprom, 0, sizeof(phy_data->sfp_eeprom));
> }
>
> +/* phy_detach()/phy_device_remove(), called from xgbe_phy_free_phy_device()
> + * below, require RTNL to be held by the caller (phy_detach() itself uses
> + * rtnl_dereference() and phy_link_topo_del_phy()). The callers below run
> + * from the service workqueue with no lock held, so a plain rtnl_lock()
> + * cannot be used here: xgbe_stopdev() (system workqueue) takes rtnl_lock()
[Severity: High]
Is the statement "The callers below run from the service workqueue with no
lock held" accurate? xgbe_phy_sfp_detect() has a second caller,
xgbe_phy_start() (phy_impl.start), which runs with RTNL already held by the
current task:
xgbe_open() (ndo_open, RTNL taken by the netdev core)
xgbe_restart() (rtnl_lock() before xgbe_restart_dev())
xgbe_change_mtu() -> xgbe_restart_dev()
xgbe_start()
pdata->phy_if.phy_impl.start()
xgbe_phy_start()
xgbe_phy_sfp_detect()
rtnl_trylock() is mutex_trylock(&rtnl_mutex), and mutex_trylock() fails when
the current task already owns the mutex. So on the ifup / restart / MTU
change path, don't both new helpers become deterministic no-ops?
That drops more than the RTNL-requiring phy_detach(): all of
xgbe_phy_sfp_mod_absent()'s pure software bookkeeping (sfp_phy_avail = 0,
sfp_changed = 0, and the memset of sfp_eeprom above) needs no lock at all,
yet it is now only reachable through the trylock wrapper.
Would it make sense to split the RTNL-requiring free from the software state
reset that must always run, and handle the caller-already-holds-RTNL case
explicitly?
> + * and then calls flush_workqueue(pdata->dev_workqueue) inside xgbe_stop(),
> + * which would block waiting for this very (dev_workqueue) work item to
> + * finish - while it is blocked waiting to reacquire RTNL from
> + * xgbe_stopdev(). That is an ABBA deadlock, the same class of bug this
> + * driver just fixed elsewhere.
> + *
> + * Use a non-blocking rtnl_trylock() instead: on contention, skip the
> + * teardown for this poll and let the next service poll (100ms-1s later)
> + * retry it. If the interface is going down concurrently, xgbe_phy_stop()
> + * (phy_impl.stop) frees the PHY itself, under RTNL already held by its
> + * own caller - so nothing is lost by skipping here.
> + */
> +static void xgbe_phy_sfp_mod_absent_safe(struct xgbe_prv_data *pdata)
> +{
> + if (!rtnl_trylock())
> + return;
> +
> + xgbe_phy_sfp_mod_absent(pdata);
> +
> + rtnl_unlock();
> +}
[Severity: High]
When the trylock loses here, the whole module-absent transition is skipped,
but xgbe_phy_sfp_detect() still falls through to xgbe_phy_sfp_phy_settings()
as though it had been committed. Can that wedge the port?
xgbe_phy_sfp_mod_absent() is the only place that zeroes phy_data->sfp_eeprom
and clears sfp_phy_avail/sfp_changed; xgbe_phy_sfp_reset() does not touch
sfp_eeprom:
static void xgbe_phy_sfp_reset(struct xgbe_phy_data *phy_data)
{
phy_data->sfp_rx_los = 0;
phy_data->sfp_tx_fault = 0;
phy_data->sfp_mod_absent = 1;
phy_data->sfp_base = XGBE_SFP_BASE_UNKNOWN;
...
}
So after a removal where the trylock failed, the old EEPROM stays cached.
If the module is re-inserted before a later poll wins the trylock,
xgbe_phy_sfp_read_eeprom() compares against that never-zeroed cache, finds
it identical and takes the else branch:
} else {
phy_data->sfp_changed = 0;
}
and from then on xgbe_phy_sfp_external_phy() early-returns:
if (!phy_data->sfp_changed)
return;
so sfp_phy_avail is never re-validated, xgbe_phy_find_phy_device() returns 0
on the "!sfp_phy_avail" check, and xgbe_phy_sfp_phy_settings() early-returns
too:
if (!phy_data->sfp_mod_absent && !phy_data->sfp_changed)
return;
leaving pdata->phy.lks stuck in the absent-module capability set published
during the removal. Does the port then stay unlinkable until an ifdown/ifup
or a physical re-seat?
The same loss applies to the new comm-ownership fallback added further down,
which calls this helper to "fall back to no module": if the trylock fails
there, sfp_changed stays 1 and sfp_eeprom stays committed to the new module,
which is exactly the half-initialized state that branch is meant to prevent.
> +
> +static void xgbe_phy_free_phy_device_safe(struct xgbe_prv_data *pdata)
> +{
> + if (!rtnl_trylock())
> + return;
> +
> + xgbe_phy_free_phy_device(pdata);
> +
> + rtnl_unlock();
> +}
> +
> static void xgbe_phy_sfp_reset(struct xgbe_phy_data *phy_data)
> {
> phy_data->sfp_rx_los = 0;
[ ... ]
> @@ -1296,26 +1339,55 @@ static void xgbe_phy_sfp_detect(struct xgbe_prv_data *pdata)
> /* Read the SFP signals and check for module presence */
> xgbe_phy_sfp_signals(pdata);
> if (phy_data->sfp_mod_absent) {
> - xgbe_phy_sfp_mod_absent(pdata);
> - goto put;
> + /* xgbe_phy_sfp_mod_absent() calls xgbe_phy_free_phy_device(),
> + * which can call back into this driver's MDIO read/write
> + * routines via phy_detach() -> phy_suspend(). Those routines
> + * take the comm ownership mutex themselves, so it must be
> + * released before making this call.
> + */
> + xgbe_phy_put_comm_ownership(pdata);
> + xgbe_phy_sfp_mod_absent_safe(pdata);
> + goto settings;
> }
>
> ret = xgbe_phy_sfp_read_eeprom(pdata);
> + xgbe_phy_put_comm_ownership(pdata);
> if (ret) {
> /* Treat any error as if there isn't an SFP plugged in */
> xgbe_phy_sfp_reset(phy_data);
> - xgbe_phy_sfp_mod_absent(pdata);
> - goto put;
> + xgbe_phy_sfp_mod_absent_safe(pdata);
> + goto settings;
> }
>
> + /* Same reasoning as above: this must run without the comm
> + * ownership mutex held.
> + */
> + if (phy_data->sfp_changed)
> + xgbe_phy_free_phy_device_safe(pdata);
[Severity: High]
Is the deferred free lost for good when rtnl_trylock() fails here? The
commit message says:
"on contention, skip the teardown for this poll and let the
next service poll (100ms-1s later) retry it"
but nothing appears to record that the teardown is still pending. The only
condition that reaches this call is sfp_changed, and
xgbe_phy_sfp_read_eeprom() already wrote the new EEPROM into
phy_data->sfp_eeprom in the same pass that set sfp_changed = 1, so the next
poll sees an identical memcmp() and sets sfp_changed = 0.
After that:
- xgbe_phy_free_phy_device_safe() is never called again
- xgbe_phy_sfp_external_phy() returns early on "if (!phy_data->sfp_changed)"
so sfp_phy_avail is never re-evaluated
- xgbe_phy_find_phy_device() returns immediately:
/* If we already have a PHY, just return */
if (phy_data->phydev)
return 0;
and xgbe_phy_link_status() keeps gating link-up on the stale phy_device:
if (phy_data->phydev) {
ret = phy_read_status(phy_data->phydev);
if (ret < 0)
return 0;
Since RTNL is global, doesn't any concurrent ip/ethtool/netlink operation on
any interface in the system make the trylock fail for the one poll in which
the change is observed? Would it be better to commit sfp_eeprom only after
a successful teardown, or to keep a sticky "needs free / needs reprobe" flag
so the next poll can genuinely retry?
> xgbe_phy_sfp_parse_eeprom(pdata);
>
> - xgbe_phy_sfp_external_phy(pdata);
> + /* Re-acquire ownership for the external PHY access below; it talks
> + * to the SFP over I2C directly and needs the mutex held again.
> + */
> + ret = xgbe_phy_get_comm_ownership(pdata);
> + if (!ret) {
> + xgbe_phy_sfp_external_phy(pdata);
> + xgbe_phy_put_comm_ownership(pdata);
> + } else {
> + /* Could not finish bringing up the new module: sfp_changed,
> + * sfp_eeprom and sfp_base/sfp_speed were already updated
> + * above for it, but external_phy() (and thus sfp_phy_avail)
> + * never ran. Fall back to "no module" state instead of
> + * committing to a half-initialized one - same pattern as
> + * the read_eeprom() failure path above.
> + */
> + xgbe_phy_sfp_reset(phy_data);
> + xgbe_phy_sfp_mod_absent_safe(pdata);
> + }
>
> -put:
> +settings:
> xgbe_phy_sfp_phy_settings(pdata);
> -
> - xgbe_phy_put_comm_ownership(pdata);
> }
--
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260918142238.191589-1-ssvatenko%40iit.org.ua
© 2016 - 2026 Red Hat, Inc.