fs: namespace preemption fix

On RT we cannot loop with preemption disabled here as
mnt_make_readonly() might have been preempted. We can safely enable
preemption while waiting for MNT_WRITE_HOLD to be cleared. Safe on !RT
as well.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/fs/namespace.c b/fs/namespace.c
index f07c7691ace19afb011c190e94b696abfd3417be..02b2deacfaac138d297022f2e0a0c534ae79f2bc 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -353,8 +353,11 @@ int __mnt_want_write(struct vfsmount *m)
         * incremented count after it has set MNT_WRITE_HOLD.
         */
        smp_mb();
-       while (ACCESS_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)
+       while (ACCESS_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD) {
+               preempt_enable();
                cpu_relax();
+               preempt_disable();
+       }
        /*
         * After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will
         * be set to match its requirements. So we must not load that until