Hi Trond,
On 8 Oct 2023, at 14:20, trondmy@xxxxxxxxxx wrote:
> From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
>
> We are not allowed to call pnfs_mark_matching_lsegs_return() without
> also holding a reference to the layout header, since doing so could lead
> to the reference count going to zero when we call
> pnfs_layout_remove_lseg(). This again can lead to a hang when we get to
> nfs4_evict_inode() and are unable to clear the layout pointer.
>
> pnfs_layout_return_unused_byserver() is guilty of this behaviour, and
> has been seen to trigger the refcount warning prior to a hang.
>
> Fixes: b6d49ecd1081 ("NFSv4: Fix a pNFS layout related use-after-free race when freeing the inode")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> ---
> fs/nfs/pnfs.c | 33 +++++++++++++++++++++++----------
> 1 file changed, 23 insertions(+), 10 deletions(-)
>
> diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
> index 63904a372b2f..21a365357629 100644
> --- a/fs/nfs/pnfs.c
> +++ b/fs/nfs/pnfs.c
> @@ -2638,31 +2638,44 @@ pnfs_should_return_unused_layout(struct pnfs_layout_hdr *lo,
> return mode == 0;
> }
>
> -static int
> -pnfs_layout_return_unused_byserver(struct nfs_server *server, void *data)
> +static int pnfs_layout_return_unused_byserver(struct nfs_server *server,
> + void *data)
> {
> const struct pnfs_layout_range *range = data;
> + const struct cred *cred;
> struct pnfs_layout_hdr *lo;
> struct inode *inode;
> + nfs4_stateid stateid;
> + enum pnfs_iomode iomode;
> +
> restart:
> rcu_read_lock();
> list_for_each_entry_rcu(lo, &server->layouts, plh_layouts) {
> - if (!pnfs_layout_can_be_returned(lo) ||
> + inode = lo->plh_inode;
> + if (!inode || !pnfs_layout_can_be_returned(lo) ||
> test_bit(NFS_LAYOUT_RETURN_REQUESTED, &lo->plh_flags))
> continue;
> - inode = lo->plh_inode;
> spin_lock(&inode->i_lock);
> - if (!pnfs_should_return_unused_layout(lo, range)) {
> + if (!lo->plh_inode ||
> + !pnfs_should_return_unused_layout(lo, range)) {
> spin_unlock(&inode->i_lock);
> continue;
> }
> + pnfs_get_layout_hdr(lo);
We're getting a crash with the nfs_inode.layout == NULL in writeback.
We haven't bisected to this yet, but I think this change is exposing the
case where the pnfs_layout_hdr refcount goes to zero, but we can still find
it here on server->layouts, and bump the refcount incorrectly.
Plausible? We can send a fix or test one..
Ben
