• Al Viro's avatar
    Fix incomplete __mntput locking · 1a88b536
    Al Viro authored
    Getting this wrong caused
    
    	WARNING: at fs/namespace.c:636 mntput_no_expire+0xac/0xf2()
    
    due to optimistically checking cpu_writer->mnt outside the spinlock.
    
    Here's what we really want:
     * we know that nobody will set cpu_writer->mnt to mnt from now on
     * all changes to that sucker are done under cpu_writer->lock
     * we want the laziest equivalent of
    	spin_lock(&cpu_writer->lock);
    	if (likely(cpu_writer->mnt != mnt)) {
    		spin_unlock(&cpu_writer->lock);
    		continue;
    	}
    	/* do stuff */
      that would make sure we won't miss earlier setting of ->mnt done by
      another CPU.
    
    Anyway, for now we just move the spin_lock() earlier and move the test
    into the properly locked region.
    Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
    Reported-and-tested-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    1a88b536
namespace.c 58 KB