Commit 2e2d4650 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'fs.rt.v5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux 

Pull mount attributes PREEMPT_RT update from Christian Brauner:
 "This contains Sebastian's fix to make changing mount
  attributes/getting write access compatible with CONFIG_PREEMPT_RT.

  The change only applies when users explicitly opt-in to real-time via
  CONFIG_PREEMPT_RT otherwise things are exactly as before. We've waited
  quite a long time with this to make sure folks could take a good look"

* tag 'fs.rt.v5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  fs/namespace: Boost the mount_lock.lock owner instead of spinning on PREEMPT_RT.
parents 15f2e3d6 0f8821da

fs/namespace.c

+18 −2
Original line number Diff line number Diff line
@@ -344,8 +344,24 @@ int __mnt_want_write(struct vfsmount *m) 
	 * incremented count after it has set MNT_WRITE_HOLD.

	 */

	smp_mb();

	while (READ_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)

	might_lock(&mount_lock.lock);

	while (READ_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD) {

		if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {

			cpu_relax();

		} else {

			/*

			 * This prevents priority inversion, if the task

			 * setting MNT_WRITE_HOLD got preempted on a remote

			 * CPU, and it prevents life lock if the task setting

			 * MNT_WRITE_HOLD has a lower priority and is bound to

			 * the same CPU as the task that is spinning here.

			 */

			preempt_enable();

			lock_mount_hash();

			unlock_mount_hash();

			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