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Subject[tip: locking/core] PCI/switchtec: Fix init_completion race condition with poll_wait()
The following commit has been merged into the locking/core branch of tip:

Commit-ID: efbdc769601f4d50018bf7ca50fc9f7c67392ece
Gitweb: https://git.kernel.org/tip/efbdc769601f4d50018bf7ca50fc9f7c67392ece
Author: Logan Gunthorpe <logang@deltatee.com>
AuthorDate: Sat, 21 Mar 2020 12:25:45 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Sat, 21 Mar 2020 16:00:20 +01:00

PCI/switchtec: Fix init_completion race condition with poll_wait()

The call to init_completion() in mrpc_queue_cmd() can theoretically
race with the call to poll_wait() in switchtec_dev_poll().

poll() write()
switchtec_dev_poll() switchtec_dev_write()
poll_wait(&s->comp.wait); mrpc_queue_cmd()
init_completion(&s->comp)
init_waitqueue_head(&s->comp.wait)

To my knowledge, no one has hit this bug.

Fix this by using reinit_completion() instead of init_completion() in
mrpc_queue_cmd().

Fixes: 080b47def5e5 ("MicroSemi Switchtec management interface driver")

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lkml.kernel.org/r/20200313183608.2646-1-logang@deltatee.com
---
drivers/pci/switch/switchtec.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/switch/switchtec.c b/drivers/pci/switch/switchtec.c
index a823b4b..81dc7ac 100644
--- a/drivers/pci/switch/switchtec.c
+++ b/drivers/pci/switch/switchtec.c
@@ -175,7 +175,7 @@ static int mrpc_queue_cmd(struct switchtec_user *stuser)
kref_get(&stuser->kref);
stuser->read_len = sizeof(stuser->data);
stuser_set_state(stuser, MRPC_QUEUED);
- init_completion(&stuser->comp);
+ reinit_completion(&stuser->comp);
list_add_tail(&stuser->list, &stdev->mrpc_queue);

mrpc_cmd_submit(stdev);
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