[PATCH RFC v4 25/25] fs: stop rewriting paths for PF_EXITING | PF_DUMPCORE

[Christian Brauner <brauner@kernel.org>]

Skip exiting and core-dumping tasks when rewriting fs_struct paths in
chroot_fs_refs(). Such a task is about to release its fs_struct via
exit_fs() anyway, so the worst case is that it lingers on a stale
root/pwd until it does.

This isn't entirely free: a skipped task keeps its reference on the old
root, so after a pivot_root() the old root can't be torn down until the
task is gone. With umount2(MNT_DETACH) that only defers destruction of
the old rootfs; a plain umount() could in principle fail with -EBUSY.
In practice this doesn't matter -- pivot_root(2) is meant to be paired
with MNT_DETACH and isn't issued while other tasks are actively using
the mount namespace -- so the transient pin is harmless.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/fs_struct.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/fs_struct.c b/fs/fs_struct.c
index 2a98cfbedd32..34699f3b6f88 100644
--- a/fs/fs_struct.c
+++ b/fs/fs_struct.c
@@ -61,8 +61,7 @@ void chroot_fs_refs(const struct path *old_root, const struct path *new_root)
 
 	read_lock(&tasklist_lock);
 	for_each_process_thread(g, p) {
-		/* leave kthreads alone */
-		if (p->flags & PF_KTHREAD)
+		if (p->flags & (PF_KTHREAD | PF_EXITING | PF_DUMPCORE))
 			continue;
 
 		task_lock(p);

-- 
2.47.3