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authorSaravana Kannan <saravanak@google.com>2021-09-15 10:09:37 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2021-10-07 07:53:17 +0200
commite554f26ea453b02fc816bc14586814a31dcdcd6a (patch)
tree4fc9f3bf4b197aaa7ba6dd3e70de07ef973f239d
parent133578ac70a26b5ee31b308a740cb0362bb3b032 (diff)
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driver core: fw_devlink: Improve handling of cyclic dependencies
commit 2de9d8e0d2fe3a1eb632def2245529067cb35db5 upstream. When we have a dependency of the form: Device-A -> Device-C Device-B Device-C -> Device-B Where, * Indentation denotes "child of" parent in previous line. * X -> Y denotes X is consumer of Y based on firmware (Eg: DT). We have cyclic dependency: device-A -> device-C -> device-B -> device-A fw_devlink current treats device-C -> device-B dependency as an invalid dependency and doesn't enforce it but leaves the rest of the dependencies as is. While the current behavior is necessary, it is not sufficient if the false dependency in this example is actually device-A -> device-C. When this is the case, device-C will correctly probe defer waiting for device-B to be added, but device-A will be incorrectly probe deferred by fw_devlink waiting on device-C to probe successfully. Due to this, none of the devices in the cycle will end up probing. To fix this, we need to go relax all the dependencies in the cycle like we already do in the other instances where fw_devlink detects cycles. A real world example of this was reported[1] and analyzed[2]. [1] - https://lore.kernel.org/lkml/0a2c4106-7f48-2bb5-048e-8c001a7c3fda@samsung.com/ [2] - https://lore.kernel.org/lkml/CAGETcx8peaew90SWiux=TyvuGgvTQOmO4BFALz7aj0Za5QdNFQ@mail.gmail.com/ Fixes: f9aa460672c9 ("driver core: Refactor fw_devlink feature") Cc: stable <stable@vger.kernel.org> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com> Signed-off-by: Saravana Kannan <saravanak@google.com> Link: https://lore.kernel.org/r/20210915170940.617415-2-saravanak@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/base/core.c17
1 files changed, 12 insertions, 5 deletions
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 3d2fc70b9951..56f54e6eb987 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1790,14 +1790,21 @@ static int fw_devlink_create_devlink(struct device *con,
* be broken by applying logic. Check for these types of cycles and
* break them so that devices in the cycle probe properly.
*
- * If the supplier's parent is dependent on the consumer, then
- * the consumer-supplier dependency is a false dependency. So,
- * treat it as an invalid link.
+ * If the supplier's parent is dependent on the consumer, then the
+ * consumer and supplier have a cyclic dependency. Since fw_devlink
+ * can't tell which of the inferred dependencies are incorrect, don't
+ * enforce probe ordering between any of the devices in this cyclic
+ * dependency. Do this by relaxing all the fw_devlink device links in
+ * this cycle and by treating the fwnode link between the consumer and
+ * the supplier as an invalid dependency.
*/
sup_dev = fwnode_get_next_parent_dev(sup_handle);
if (sup_dev && device_is_dependent(con, sup_dev)) {
- dev_dbg(con, "Not linking to %pfwP - False link\n",
- sup_handle);
+ dev_info(con, "Fixing up cyclic dependency with %pfwP (%s)\n",
+ sup_handle, dev_name(sup_dev));
+ device_links_write_lock();
+ fw_devlink_relax_cycle(con, sup_dev);
+ device_links_write_unlock();
ret = -EINVAL;
} else {
/*