[PATCH 4.4 018/188] s390/cio: dont call css_wait_for_slow_path() inside a lock

Greg Kroah-Hartman
2021-07-19T14:56:57Z

From: Vineeth Vijayan <vneethv@linux.ibm.com>

commit c749d8c018daf5fba6dfac7b6c5c78b27efd7d65 upstream.

Currently css_wait_for_slow_path() gets called inside the chp->lock.
The path-verification-loop of slowpath inside this lock could lead to
deadlock as reported by the lockdep validator.

The ccw_device_get_chp_desc() during the instance of a device-set-online
would try to acquire the same 'chp->lock' to read the chp->desc.
The instance of this function can get called from multiple scenario,
like probing or setting-device online manually. This could, in some
corner-cases lead to the deadlock.

lockdep validator reported this as,

CPU0 CPU1
---- ----
lock(&chp->lock);
lock(kn->active#43);
lock(&chp->lock);
lock((wq_completion)cio);

The chp->lock was introduced to serialize the access of struct
channel_path. This lock is not needed for the css_wait_for_slow_path()
function, so invoke the slow-path function outside this lock.

Fixes: b730f3a93395 ("[S390] cio: add lock to struct channel_path")
Cc: <stable@vger.kernel.org>
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/s390/cio/chp.c | 3 +++
drivers/s390/cio/chsc.c | 2 --
2 files changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/s390/cio/chp.c
+++ b/drivers/s390/cio/chp.c
@@ -257,6 +257,9 @@ static ssize_t chp_status_write(struct d
if (!num_args)
return count;

+ /* Wait until previous actions have settled. */
+ css_wait_for_slow_path();
+
if (!strncasecmp(cmd, "on", 2) || !strcmp(cmd, "1")) {
mutex_lock(&cp->lock);
error = s390_vary_chpid(cp->chpid, 1);
--- a/drivers/s390/cio/chsc.c
+++ b/drivers/s390/cio/chsc.c
@@ -769,8 +769,6 @@ int chsc_chp_vary(struct chp_id chpid, i
{
struct channel_path *chp = chpid_to_chp(chpid);

- /* Wait until previous actions have settled. */
- css_wait_for_slow_path();
/*
* Redo PathVerification on the devices the chpid connects to
*/