Messages in this thread | | | Date | Fri, 15 Sep 2017 16:29:11 -0700 | From | Jaegeuk Kim <> | Subject | Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion |
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On 09/15, Theodore Ts'o wrote: > On Fri, Sep 15, 2017 at 11:44:33AM -0700, Jaegeuk Kim wrote: > > > > So, I digged it in more detail, and found, in drivers/android/binder.c [1], > > - binder_ioctl() > > - create a kernel thread > > - zombie_cleanup_check() > > - binder_defer_work() > > - queue_work(..., &binder_deferred_work); > > > > - binder_deferred_func() > > - binder_clear_zombies() > > - binder_proc_clear_zombies() > > - put_files_struct() > > - close_files() > > - filp_close() > > - fput() > > > > It seems binder holds some proc files. > > If binder was holding some files open, then umount should have failed > with EBUSY, no?
Based on what I've got some traces so far,
- binder_ioctl - create a kernel thread - zombie_cleanup_check - binder_defer_work - queue_work(..., &binder_deferred_work);
- binder_deferred_func - binder_clear_zombies - binder_proc_clear_zombies - put_files_struct - close_files - filp_close - fput
- delayed_fput ... - file_free - dput init - umount - mntput - mntput_no_expire - do_umount - mnt_get_count() > 2 - mntput_no_expire - mnt_add_count(-1); - mnt_add_count(-1); - mnt_get_count() return; - return 0; - delayed_mntput_work - device_shutdown - ext4_put_super() - EIO, and panic if error=panic
The mntput() in delayed_fput() is the last function call. So before that moment, sys_umount() may see mnt_get_count() as 2, so it avoids EBUSY condition. I'm not sure why it check over 2 tho.
> > Does Android use mount namespaces at all? > > - Ted
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