On Mon, Nov 15, 2021 at 03:16:45PM +0200, Ioanna Alifieraki wrote: > Currently when removing an ipmi_user the removal is deferred as a work on > the system's workqueue. Although this guarantees the free operation will > occur in non atomic context, it can race with the ipmi_msghandler module > removal (see [1]) . In case a remove_user work is scheduled for removal > and shortly after ipmi_msghandler module is removed we can end up in a > situation where the module is removed fist and when the work is executed > the system crashes with : > BUG: unable to handle page fault for address: ffffffffc05c3450 > PF: supervisor instruction fetch in kernel mode > PF: error_code(0x0010) - not-present page > because the pages of the module are gone. In cleanup_ipmi() there is no > easy way to detect if there are any pending works to flush them before > removing the module. This patch creates a separate workqueue and schedules > the remove_work works on it. When removing the module the workqueue is > drained when destroyed to avoid the race.
Thanks, this is in my for-next queue. If nobody complains after a week or so I'll send it on. -corey > > [1] https://bugs.launchpad.net/bugs/1950666 > > Cc: sta...@vger.kernel.org > Fixes: 3b9a907223d7 (ipmi: fix sleep-in-atomic in free_user at cleanup SRCU > user->release_barrier) > Signed-off-by: Ioanna Alifieraki <ioanna-maria.alifier...@canonical.com> > --- > drivers/char/ipmi/ipmi_msghandler.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/drivers/char/ipmi/ipmi_msghandler.c > b/drivers/char/ipmi/ipmi_msghandler.c > index deed355422f4..1ade72bfae0f 100644 > --- a/drivers/char/ipmi/ipmi_msghandler.c > +++ b/drivers/char/ipmi/ipmi_msghandler.c > @@ -191,6 +191,8 @@ struct ipmi_user { > struct work_struct remove_work; > }; > > +struct workqueue_struct *remove_work_wq; > + > static struct ipmi_user *acquire_ipmi_user(struct ipmi_user *user, int > *index) > __acquires(user->release_barrier) > { > @@ -1297,7 +1299,7 @@ static void free_user(struct kref *ref) > struct ipmi_user *user = container_of(ref, struct ipmi_user, refcount); > > /* SRCU cleanup must happen in task context. */ > - schedule_work(&user->remove_work); > + queue_work(remove_work_wq, &user->remove_work); > } > > static void _ipmi_destroy_user(struct ipmi_user *user) > @@ -5383,6 +5385,13 @@ static int ipmi_init_msghandler(void) > > atomic_notifier_chain_register(&panic_notifier_list, &panic_block); > > + remove_work_wq = > create_singlethread_workqueue("ipmi-msghandler-remove-wq"); > + if (!remove_work_wq) { > + pr_err("unable to create ipmi-msghandler-remove-wq workqueue"); > + rv = -ENOMEM; > + goto out; > + } > + > initialized = true; > > out: > @@ -5408,6 +5417,8 @@ static void __exit cleanup_ipmi(void) > int count; > > if (initialized) { > + destroy_workqueue(remove_work_wq); > + > atomic_notifier_chain_unregister(&panic_notifier_list, > &panic_block); > > -- > 2.17.1 > _______________________________________________ Openipmi-developer mailing list Openipmi-developer@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/openipmi-developer
