+ mm-remove-nrexceptional-from-inode-remove-bug_on.patch added to -mm tree

+ mm-remove-nrexceptional-from-inode-remove-bug_on.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm: remove nrexceptional from inode: remove BUG_ON
has been added to the -mm tree.  Its filename is
     mm-remove-nrexceptional-from-inode-remove-bug_on.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-remove-nrexceptional-from-inode-remove-bug_on.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-remove-nrexceptional-from-inode-remove-bug_on.patch

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------------------------------------------------------
From: Hugh Dickins <hughd@google.com>
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/alpine.LSU.2.11.2104292229380.16080@eggly.anvils
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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

--- 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));
_

Patches currently in -mm which might be from hughd@google.com are

mm-remove-nrexceptional-from-inode-remove-bug_on.patch
mm-restore-node-stat-checking-in-proc-sys-vm-stat_refresh.patch
mm-no-more-einval-from-proc-sys-vm-stat_refresh.patch
mm-proc-sys-vm-stat_refresh-skip-checking-known-negative-stats.patch
mm-proc-sys-vm-stat_refresh-stop-checking-monotonic-numa-stats.patch