linux-kernel - [PATCH 4.19 5/7] proc: Clear the pieces of proc_inode that proc_evict

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Date:   Thu,  7 Jan 2021 15:53:12 +0800
From:   Wen Yang <wenyang@...ux.alibaba.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sasha Levin <sashal@...nel.org>
Cc:     Xunlei Pang <xlpang@...ux.alibaba.com>,
        linux-kernel@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        stable@...r.kernel.org, Wen Yang <wenyang@...ux.alibaba.com>
Subject: [PATCH 4.19 5/7] proc: Clear the pieces of proc_inode that proc_evict_inode cares about

From: "Eric W. Biederman" <ebiederm@...ssion.com>

[ Upstream commit 71448011ea2a1cd36d8f5cbdab0ed716c454d565 ]

This just keeps everything tidier, and allows for using flags like
SLAB_TYPESAFE_BY_RCU where slabs are not always cleared before reuse.
I don't see reuse without reinitializing happening with the proc_inode
but I had a false alarm while reworking flushing of proc dentries and
indoes when a process dies that caused me to tidy this up.

The code is a little easier to follow and reason about this
way so I figured the changes might as well be kept.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: <stable@...r.kernel.org> # 4.19.x
Signed-off-by: Wen Yang <wenyang@...ux.alibaba.com>
---
 fs/proc/inode.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index fffc7e4..45b4344 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -34,21 +34,27 @@ static void proc_evict_inode(struct inode *inode)
 {
 	struct proc_dir_entry *de;
 	struct ctl_table_header *head;
+	struct proc_inode *ei = PROC_I(inode);
 
 	truncate_inode_pages_final(&inode->i_data);
 	clear_inode(inode);
 
 	/* Stop tracking associated processes */
-	put_pid(PROC_I(inode)->pid);
+	if (ei->pid) {
+		put_pid(ei->pid);
+		ei->pid = NULL;
+	}
 
 	/* Let go of any associated proc directory entry */
-	de = PDE(inode);
-	if (de)
+	de = ei->pde;
+	if (de) {
 		pde_put(de);
+		ei->pde = NULL;
+	}
 
-	head = PROC_I(inode)->sysctl;
+	head = ei->sysctl;
 	if (head) {
-		RCU_INIT_POINTER(PROC_I(inode)->sysctl, NULL);
+		RCU_INIT_POINTER(ei->sysctl, NULL);
 		proc_sys_evict_inode(inode, head);
 	}
 }
-- 
1.8.3.1