linux-kernel - [PATCH] fs: nfs: fix a possible sleep-in-atomic-context bug in _pnfs_grab_empty

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Date:   Tue, 17 Dec 2019 21:33:19 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     trond.myklebust@...merspace.com, anna.schumaker@...app.com
Cc:     linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH] fs: nfs: fix a possible sleep-in-atomic-context bug in _pnfs_grab_empty_layout()

The filesystem may sleep while holding a spinlock.
The function call path (from bottom to top) in Linux 4.19 is:

fs/nfs/pnfs.c, 2052: 
	pnfs_find_alloc_layout(GFP_KERNEL) in _pnfs_grab_empty_layout
fs/nfs/pnfs.c, 2051: 
	spin_lock in _pnfs_grab_empty_layout

pnfs_find_alloc_layout(GFP_KERNEL) can sleep at runtime.

To fix this possible bug, GFP_KERNEL is replaced with GFP_ATOMIC for
pnfs_find_alloc_layout().

This bug is found by a static analysis tool STCheck written by myself.

Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
---
 fs/nfs/pnfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index cec3070ab577..cfbe170f0651 100644
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -2138,7 +2138,7 @@ _pnfs_grab_empty_layout(struct inode *ino, struct nfs_open_context *ctx)
 	struct pnfs_layout_hdr *lo;
 
 	spin_lock(&ino->i_lock);
-	lo = pnfs_find_alloc_layout(ino, ctx, GFP_KERNEL);
+	lo = pnfs_find_alloc_layout(ino, ctx, GFP_ATOMIC);
 	if (!lo)
 		goto out_unlock;
 	if (!test_bit(NFS_LAYOUT_INVALID_STID, &lo->plh_flags))
-- 
2.17.1