linux-kernel - [for-linus][PATCH 1/5] eventfs: Use GFP_NOFS for allocation when eventfs

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Date:   Thu, 23 Nov 2023 12:25:40 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josef Bacik <josef@...icpanda.com>
Subject: [for-linus][PATCH 1/5] eventfs: Use GFP_NOFS for allocation when eventfs_mutex is held

From: "Steven Rostedt (Google)" <rostedt@...dmis.org>

If memory reclaim happens, it can reclaim file system pages. The file
system pages from eventfs may take the eventfs_mutex on reclaim. This
means that allocation while holding the eventfs_mutex must not call into
filesystem reclaim. A lockdep splat uncovered this.

Link: https://lkml.kernel.org/r/20231121231112.373501894@goodmis.org

Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Fixes: 28e12c09f5aa0 ("eventfs: Save ownership and mode")
Fixes: 5790b1fb3d672 ("eventfs: Remove eventfs_file and just use eventfs_inode")
Reported-by: Mark Rutland <mark.rutland@....com>
Reviewed-by: Josef Bacik <josef@...icpanda.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 fs/tracefs/event_inode.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 3eb6c622a74d..56d192f0ead8 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -95,7 +95,7 @@ static int eventfs_set_attr(struct mnt_idmap *idmap, struct dentry *dentry,
 	if (!(dentry->d_inode->i_mode & S_IFDIR)) {
 		if (!ei->entry_attrs) {
 			ei->entry_attrs = kzalloc(sizeof(*ei->entry_attrs) * ei->nr_entries,
-						  GFP_KERNEL);
+						  GFP_NOFS);
 			if (!ei->entry_attrs) {
 				ret = -ENOMEM;
 				goto out;
@@ -627,7 +627,7 @@ static int add_dentries(struct dentry ***dentries, struct dentry *d, int cnt)
 {
 	struct dentry **tmp;
 
-	tmp = krealloc(*dentries, sizeof(d) * (cnt + 2), GFP_KERNEL);
+	tmp = krealloc(*dentries, sizeof(d) * (cnt + 2), GFP_NOFS);
 	if (!tmp)
 		return -1;
 	tmp[cnt] = d;
-- 
2.42.0