[005/143] mm: remove nrexceptional from inode: remove BUG_ON

Commit Message

Andrew Morton May 5, 2021, 1:32 a.m. UTC

From: Hugh Dickins <[e-mail]>
Subject: mm: remove nrexceptional from inode: remove BUG_ON

clear_inode()'s BUG_ON(!mapping_empty(&inode->i_data)) is unsafe: we know
of two ways in which nodes can and do (on rare occasions) get left behind.
Until those are fixed, do not BUG_ON() nor even WARN_ON().  Yes, this
will then leak those nodes (or the next user of the struct inode may use
them); but this has been happening for years, and the new
BUG_ON(!mapping_empty) was only guilty of revealing that.  A proper fix
will follow, but no hurry.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Hugh Dickins <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 fs/inode.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

Patch

--- a/fs/inode.c~mm-remove-nrexceptional-from-inode-remove-bug_on
+++ a/fs/inode.c
@@ -529,7 +529,14 @@  void clear_inode(struct inode *inode)
 	 */
 	xa_lock_irq(&inode->i_data.i_pages);
 	BUG_ON(inode->i_data.nrpages);
-	BUG_ON(!mapping_empty(&inode->i_data));
+	/*
+	 * Almost always, mapping_empty(&inode->i_data) here; but there are
+	 * two known and long-standing ways in which nodes may get left behind
+	 * (when deep radix-tree node allocation failed partway; or when THP
+	 * collapse_file() failed). Until those two known cases are cleaned up,
+	 * or a cleanup function is called here, do not BUG_ON(!mapping_empty),
+	 * nor even WARN_ON(!mapping_empty).
+	 */
 	xa_unlock_irq(&inode->i_data.i_pages);
 	BUG_ON(!list_empty(&inode->i_data.private_list));
 	BUG_ON(!(inode->i_state & I_FREEING));