dm: use noio when sending kobject event

kobject_uevent may allocate memory and it may be called while there are dm
devices suspended. The allocation may recurse into a suspended device,
causing a deadlock. We must set the noio flag when sending a uevent.

The observed deadlock was reported here:
https://www.redhat.com/archives/dm-devel/2020-March/msg00025.html

Reported-by: Khazhismel Kumykov <khazhy@google.com>
Reported-by: Tahsin Erdogan <tahsin@google.com>
Reported-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 4cc7e2599664c54ab040d763095b517eef21b551..52449afd58ebb76ab6e14c9a6fa18e486639c199 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -12,6 +12,7 @@
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/sched/mm.h>
 #include <linux/sched/signal.h>
 #include <linux/blkpg.h>
 #include <linux/bio.h>
@@ -2939,17 +2940,25 @@ EXPORT_SYMBOL_GPL(dm_internal_resume_fast);
 int dm_kobject_uevent(struct mapped_device *md, enum kobject_action action,
                       unsigned cookie)
 {
+       int r;
+       unsigned noio_flag;
        char udev_cookie[DM_COOKIE_LENGTH];
        char *envp[] = { udev_cookie, NULL };
 
+       noio_flag = memalloc_noio_save();
+
        if (!cookie)
-               return kobject_uevent(&disk_to_dev(md->disk)->kobj, action);
+               r = kobject_uevent(&disk_to_dev(md->disk)->kobj, action);
        else {
                snprintf(udev_cookie, DM_COOKIE_LENGTH, "%s=%u",
                         DM_COOKIE_ENV_VAR_NAME, cookie);
-               return kobject_uevent_env(&disk_to_dev(md->disk)->kobj,
-                                         action, envp);
+               r = kobject_uevent_env(&disk_to_dev(md->disk)->kobj,
+                                      action, envp);
        }
+
+       memalloc_noio_restore(noio_flag);
+
+       return r;
 }
 
 uint32_t dm_next_uevent_seq(struct mapped_device *md)