[PATCH 6.6 090/158] interconnect: Dont access req_list while its being manipulated

Greg Kroah-Hartman
2024-04-23T21:43:37Z

From: Mike Tipton <quic_mdtipton@quicinc.com>

[ Upstream commit de1bf25b6d771abdb52d43546cf57ad775fb68a1 ]

The icc_lock mutex was split into separate icc_lock and icc_bw_lock
mutexes in [1] to avoid lockdep splats. However, this didn't adequately
protect access to icc_node::req_list.

The icc_set_bw() function will eventually iterate over req_list while
only holding icc_bw_lock, but req_list can be modified while only
holding icc_lock. This causes races between icc_set_bw(), of_icc_get(),
and icc_put().

Example A:

CPU0 CPU1
---- ----
icc_set_bw(path_a)
mutex_lock(&icc_bw_lock);
icc_put(path_b)
mutex_lock(&icc_lock);
aggregate_requests()
hlist_for_each_entry(r, ...
hlist_del(...
<r = invalid pointer>

Example B:

CPU0 CPU1
---- ----
icc_set_bw(path_a)
mutex_lock(&icc_bw_lock);
path_b = of_icc_get()
of_icc_get_by_index()
mutex_lock(&icc_lock);
path_find()
path_init()
aggregate_requests()
hlist_for_each_entry(r, ...
hlist_add_head(...
<r = invalid pointer>

Fix this by ensuring icc_bw_lock is always held before manipulating
icc_node::req_list. The additional places icc_bw_lock is held don't
perform any memory allocations, so we should still be safe from the
original lockdep splats that motivated the separate locks.

[1] commit af42269c3523 ("interconnect: Fix locking for runpm vs reclaim")

Signed-off-by: Mike Tipton <quic_mdtipton@quicinc.com>
Fixes: af42269c3523 ("interconnect: Fix locking for runpm vs reclaim")
Reviewed-by: Rob Clark <robdclark@chromium.org>
Link: https://lore.kernel.org/r/20240305225652.22872-1-quic_mdtipton@quicinc.com
Signed-off-by: Georgi Djakov <djakov@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/interconnect/core.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
index 50bac2d79d9b5..68edb07d4443e 100644
--- a/drivers/interconnect/core.c
+++ b/drivers/interconnect/core.c
@@ -176,6 +176,8 @@ static struct icc_path *path_init(struct device *dev, struct icc_node *dst,

path->num_nodes = num_nodes;

+ mutex_lock(&icc_bw_lock);
+
for (i = num_nodes - 1; i >= 0; i--) {
node->provider->users++;
hlist_add_head(&path->reqs[i].req_node, &node->req_list);
@@ -186,6 +188,8 @@ static struct icc_path *path_init(struct device *dev, struct icc_node *dst,
node = node->reverse;
}

+ mutex_unlock(&icc_bw_lock);
+
return path;
}

@@ -792,12 +796,16 @@ void icc_put(struct icc_path *path)
pr_err("%s: error (%d)\n", __func__, ret);

mutex_lock(&icc_lock);
+ mutex_lock(&icc_bw_lock);
+
for (i = 0; i < path->num_nodes; i++) {
node = path->reqs[i].node;
hlist_del(&path->reqs[i].req_node);
if (!WARN_ON(!node->provider->users))
node->provider->users--;
}
+
+ mutex_unlock(&icc_bw_lock);
mutex_unlock(&icc_lock);

kfree_const(path->name);
--
2.43.0