mm: userfaultfd: remove stale comment about core dump locking

Since commit 7f3bfab52cab ("mm/gup: take mmap_lock in get_dump_page()"),
which landed in v5.10, core dumping doesn't enter fault handling without
holding the mmap_lock anymore.  Remove the stale parts of the comments,
but leave the behavior as-is - letting core dumping block on userfault
handling would be a bad idea and could lead to deadlocks if the dumping
process was handling its own userfaults.

Link: https://lkml.kernel.org/r/20230815212216.264445-1-jannh@google.com
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 1091cb46174743a6a3ce2d3bc4688b761462948f..56eaae9dac1ab2fbd76dffbd895d4e1ca5dcddc2 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -428,15 +428,11 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
         * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
         * the no_page_table() helper in follow_page_mask(), but the
         * shmem_vm_ops->fault method is invoked even during
-        * coredumping without mmap_lock and it ends up here.
+        * coredumping and it ends up here.
         */
        if (current->flags & (PF_EXITING|PF_DUMPCORE))
                goto out;
 
-       /*
-        * Coredumping runs without mmap_lock so we can only check that
-        * the mmap_lock is held, if PF_DUMPCORE was not set.
-        */
        assert_fault_locked(vmf);
 
        ctx = vma->vm_userfaultfd_ctx.ctx;