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

[linux-block.git] / fs / namespace.c

diff --git a/fs/namespace.c b/fs/namespace.c
index 627db2e031e906ee9a4e7b8c6d9c05998af6f912..6e9844b8c6fb46295a3e09edfbb6fdebdaafe7b0 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -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)
-               cpu_relax();
+       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