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SubjectRe: [PATCH] fs: nfs: fix a possible sleep-in-atomic-context bug in _pnfs_grab_empty_layout()
Date
On Tue, 2019-12-17 at 21:33 +0800, Jia-Ju Bai wrote:
> 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@gmail.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))

I'm not seeing why this is necessary. As far as I can see,
pnfs_find_alloc_layout() will release the ino->i_lock before sleeping.

False positive?

--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com


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