[0/2,RESEND] vfs: Fix crashes when reading /proc/mounts

Message

Jan Kara Dec. 11, 2018, 5:24 p.m. UTC

Hello,

resending this patch series since I got no reply for almost two months.  This
patch series aims at fixing possible races between functions formatting output
for /proc/mounts and friends and remount. Especially ->show_options functions
of filesystems are not counting with the fact that options can change under
them and thus races can result in bogus output or outright crashes (like was
the case with ext4 handling of quota mount option, or udf could crash when
printing charset name, or xfs when printing log device name etc.).

Admittedly the patch 2/2 is somewhat ugly because namespace_sem ranks below
sb->s_umount semaphore but I think it is bearable. Al, what do you think?

								Honza