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 */