This is a note to let you know that I've just added the patch titled
binder: Don't use mmput() from shrinker function.
to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-linus branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.
If you have any questions about this process, please let me know.
>From f867c771f98891841c217fa8459244ed0dd28921 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Date: Fri, 17 Jul 2020 00:12:15 +0900
Subject: binder: Don't use mmput() from shrinker function.
syzbot is reporting that mmput() from shrinker function has a risk of
deadlock [1], for delayed_uprobe_add() from update_ref_ctr() calls
kzalloc(GFP_KERNEL) with delayed_uprobe_lock held, and
uprobe_clear_state() from __mmput() also holds delayed_uprobe_lock.
Commit a1b2289cef92ef0e ("android: binder: drop lru lock in isolate
callback") replaced mmput() with mmput_async() in order to avoid sleeping
with spinlock held. But this patch replaces mmput() with mmput_async() in
order not to start __mmput() from shrinker context.
[1] https://syzkaller.appspot.com/bug?id=bc9e7303f537c41b2b0cc2dfcea3fc42964c2d45
Reported-by: syzbot <syzbot+1068f09c44d151250c33@xxxxxxxxxxxxxxxxxxxxxxxxx>
Reported-by: syzbot <syzbot+e5344baa319c9a96edec@xxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Todd Kjos <tkjos@xxxxxxxxxx>
Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/4ba9adb2-43f5-2de0-22de-f6075c1fab50@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/android/binder_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 42c672f1584e..cbe6aa77d50d 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -947,7 +947,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
trace_binder_unmap_user_end(alloc, index);
}
mmap_read_unlock(mm);
- mmput(mm);
+ mmput_async(mm);
trace_binder_unmap_kernel_start(alloc, index);
--
2.27.0
