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Subject[PATCH v3] driver core: Update device link status correctly for SYNC_STATE_ONLY links
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When SYNC_STATE_ONLY support was added in commit 05ef983e0d65 ("driver
core: Add device link support for SYNC_STATE_ONLY flag"),
SYNC_STATE_ONLY links were treated similar to STATELESS links in terms
of not blocking consumer probe if the supplier hasn't probed yet.

That caused a SYNC_STATE_ONLY device link's status to not get updated.
Since SYNC_STATE_ONLY device link is no longer useful once the
consumer probes, commit 21c27f06587d ("driver core: Fix
SYNC_STATE_ONLY device link implementation") addresses the status
update issue by deleting the SYNC_STATE_ONLY device link instead of
complicating the status update code.

However, there are still some cases where we need to update the status
of a SYNC_STATE_ONLY device link. This is because a SYNC_STATE_ONLY
device link can later get converted into a normal MANAGED device link
when a normal MANAGED device link is created between a supplier and
consumer that already have a SYNC_STATE_ONLY device link between them.

If a SYNC_STATE_ONLY device link's status isn't maintained correctly
till it's converted to a normal MANAGED device link, then the normal
MANAGED device link will end up with a wrong link status. This can cause
a warning stack trace[1] when the consumer device probes successfully.

This commit fixes the SYNC_STATE_ONLY device link status update issue
where it wouldn't transition correctly from DL_STATE_DORMANT or
DL_STATE_AVAILABLE to DL_STATE_CONSUMER_PROBE. It also resets the status
back to DL_STATE_DORMANT or DL_STATE_AVAILABLE if the consumer probe
fails.

[1] - https://lore.kernel.org/lkml/20200522204120.3b3c9ed6@apollo/
Fixes: 05ef983e0d65 ("driver core: Add device link support for SYNC_STATE_ONLY flag")
Fixes: 21c27f06587d ("driver core: Fix SYNC_STATE_ONLY device link implementation")
Reported-by: Michael Walle <michael@walle.cc>
Tested-by: Michael Walle <michael@walle.cc>
Signed-off-by: Saravana Kannan <saravanak@google.com>
---
v1->v2:
- Added code to "revert" the link status if consumer probe fails

v2->v3:
- Fixed copy-pasta where I was checking link->status instead of
link->flags.

drivers/base/core.c | 34 ++++++++++++++++++++++++++--------
1 file changed, 26 insertions(+), 8 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 791b7530599f..9a76dd44cb37 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -646,9 +646,17 @@ static void device_links_missing_supplier(struct device *dev)
{
struct device_link *link;

- list_for_each_entry(link, &dev->links.suppliers, c_node)
- if (link->status == DL_STATE_CONSUMER_PROBE)
+ list_for_each_entry(link, &dev->links.suppliers, c_node) {
+ if (link->status != DL_STATE_CONSUMER_PROBE)
+ continue;
+
+ if (link->supplier->links.status == DL_DEV_DRIVER_BOUND) {
WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
+ } else {
+ WARN_ON(!(link->flags & DL_FLAG_SYNC_STATE_ONLY));
+ WRITE_ONCE(link->status, DL_STATE_DORMANT);
+ }
+ }
}

/**
@@ -687,11 +695,11 @@ int device_links_check_suppliers(struct device *dev)
device_links_write_lock();

list_for_each_entry(link, &dev->links.suppliers, c_node) {
- if (!(link->flags & DL_FLAG_MANAGED) ||
- link->flags & DL_FLAG_SYNC_STATE_ONLY)
+ if (!(link->flags & DL_FLAG_MANAGED))
continue;

- if (link->status != DL_STATE_AVAILABLE) {
+ if (link->status != DL_STATE_AVAILABLE &&
+ !(link->flags & DL_FLAG_SYNC_STATE_ONLY)) {
device_links_missing_supplier(dev);
ret = -EPROBE_DEFER;
break;
@@ -952,11 +960,21 @@ static void __device_links_no_driver(struct device *dev)
if (!(link->flags & DL_FLAG_MANAGED))
continue;

- if (link->flags & DL_FLAG_AUTOREMOVE_CONSUMER)
+ if (link->flags & DL_FLAG_AUTOREMOVE_CONSUMER) {
device_link_drop_managed(link);
- else if (link->status == DL_STATE_CONSUMER_PROBE ||
- link->status == DL_STATE_ACTIVE)
+ continue;
+ }
+
+ if (link->status != DL_STATE_CONSUMER_PROBE &&
+ link->status != DL_STATE_ACTIVE)
+ continue;
+
+ if (link->supplier->links.status == DL_DEV_DRIVER_BOUND) {
WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
+ } else {
+ WARN_ON(!(link->flags & DL_FLAG_SYNC_STATE_ONLY));
+ WRITE_ONCE(link->status, DL_STATE_DORMANT);
+ }
}

dev->links.status = DL_DEV_NO_DRIVER;
--
2.27.0.rc0.183.gde8f92d652-goog
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