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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Peter Oberparleiter <oberpar@linux.ibm.com>,
        Vineeth Vijayan <vneethv@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>
Subject: [PATCH 4.9 018/245] s390/cio: dont call css_wait_for_slow_path() inside a lock
Date:   Mon, 19 Jul 2021 16:49:20 +0200
Message-Id: <20210719144940.989754641@linuxfoundation.org>
In-Reply-To: <20210719144940.288257948@linuxfoundation.org>
References: <20210719144940.288257948@linuxfoundation.org>
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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
@@ -254,6 +254,9 @@ 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
 	 */