Re: [for-6.13 PATCH 02/19] nfs_common: must not hold RCU while calling nfsd_file_put_local

Jeff Layton
2024-11-13T14:58:30Z

On Fri, 2024-11-08 at 18:39 -0500, Mike Snitzer wrote:
> Move holding the RCU from nfs_to_nfsd_file_put_local to
> nfs_to_nfsd_net_put. It is the call to nfs_to->nfsd_serv_put that
> requires the RCU anyway (the puts for nfsd_file and netns were
> combined to avoid an extra indirect reference but that
> micro-optimization isn't possible now).
>
> This fixes xfstests generic/013 and it triggering:
>
> "Voluntary context switch within RCU read-side critical section!"
>
> [ 143.545738] Call Trace:
> [ 143.546206] <TASK>
> [ 143.546625] ? show_regs+0x6d/0x80
> [ 143.547267] ? __warn+0x91/0x140
> [ 143.547951] ? rcu_note_context_switch+0x496/0x5d0
> [ 143.548856] ? report_bug+0x193/0x1a0
> [ 143.549557] ? handle_bug+0x63/0xa0
> [ 143.550214] ? exc_invalid_op+0x1d/0x80
> [ 143.550938] ? asm_exc_invalid_op+0x1f/0x30
> [ 143.551736] ? rcu_note_context_switch+0x496/0x5d0
> [ 143.552634] ? wakeup_preempt+0x62/0x70
> [ 143.553358] __schedule+0xaa/0x1380
> [ 143.554025] ? _raw_spin_unlock_irqrestore+0x12/0x40
> [ 143.554958] ? try_to_wake_up+0x1fe/0x6b0
> [ 143.555715] ? wake_up_process+0x19/0x20
> [ 143.556452] schedule+0x2e/0x120
> [ 143.557066] schedule_preempt_disabled+0x19/0x30
> [ 143.557933] rwsem_down_read_slowpath+0x24d/0x4a0
> [ 143.558818] ? xfs_efi_item_format+0x50/0xc0 [xfs]
> [ 143.559894] down_read+0x4e/0xb0
> [ 143.560519] xlog_cil_commit+0x1b2/0xbc0 [xfs]
> [ 143.561460] ? _raw_spin_unlock+0x12/0x30
> [ 143.562212] ? xfs_inode_item_precommit+0xc7/0x220 [xfs]
> [ 143.563309] ? xfs_trans_run_precommits+0x69/0xd0 [xfs]
> [ 143.564394] __xfs_trans_commit+0xb5/0x330 [xfs]
> [ 143.565367] xfs_trans_roll+0x48/0xc0 [xfs]
> [ 143.566262] xfs_defer_trans_roll+0x57/0x100 [xfs]
> [ 143.567278] xfs_defer_finish_noroll+0x27a/0x490 [xfs]
> [ 143.568342] xfs_defer_finish+0x1a/0x80 [xfs]
> [ 143.569267] xfs_bunmapi_range+0x4d/0xb0 [xfs]
> [ 143.570208] xfs_itruncate_extents_flags+0x13d/0x230 [xfs]
> [ 143.571353] xfs_free_eofblocks+0x12e/0x190 [xfs]
> [ 143.572359] xfs_file_release+0x12d/0x140 [xfs]
> [ 143.573324] __fput+0xe8/0x2d0
> [ 143.573922] __fput_sync+0x1d/0x30
> [ 143.574574] nfsd_filp_close+0x33/0x60 [nfsd]
> [ 143.575430] nfsd_file_free+0x96/0x150 [nfsd]
> [ 143.576274] nfsd_file_put+0xf7/0x1a0 [nfsd]
> [ 143.577104] nfsd_file_put_local+0x18/0x30 [nfsd]
> [ 143.578070] nfs_close_local_fh+0x101/0x110 [nfs_localio]
> [ 143.579079] __put_nfs_open_context+0xc9/0x180 [nfs]
> [ 143.580031] nfs_file_clear_open_context+0x4a/0x60 [nfs]
> [ 143.581038] nfs_file_release+0x3e/0x60 [nfs]
> [ 143.581879] __fput+0xe8/0x2d0
> [ 143.582464] __fput_sync+0x1d/0x30
> [ 143.583108] __x64_sys_close+0x41/0x80
> [ 143.583823] x64_sys_call+0x189a/0x20d0
> [ 143.584552] do_syscall_64+0x64/0x170
> [ 143.585240] entry_SYSCALL_64_after_hwframe+0x76/0x7e
> [ 143.586185] RIP: 0033:0x7f3c5153efd7
>
> Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> ---
> fs/nfs_common/nfslocalio.c | 8 +++-----
> fs/nfsd/filecache.c | 14 +++++++-------
> fs/nfsd/filecache.h | 2 +-
> include/linux/nfslocalio.h | 18 +++++++++++++++---
> 4 files changed, 26 insertions(+), 16 deletions(-)
>
> diff --git a/fs/nfs_common/nfslocalio.c b/fs/nfs_common/nfslocalio.c
> index 09404d142d1a..a74ec08f6c96 100644
> --- a/fs/nfs_common/nfslocalio.c
> +++ b/fs/nfs_common/nfslocalio.c
> @@ -155,11 +155,9 @@ struct nfsd_file *nfs_open_local_fh(nfs_uuid_t *uuid,
> /* We have an implied reference to net thanks to nfsd_serv_try_get */
> localio = nfs_to->nfsd_open_local_fh(net, uuid->dom, rpc_clnt,
> cred, nfs_fh, fmode);
> - if (IS_ERR(localio)) {
> - rcu_read_lock();
> - nfs_to->nfsd_serv_put(net);
> - rcu_read_unlock();
> - }
> + if (IS_ERR(localio))
> + nfs_to_nfsd_net_put(net);
> +
> return localio;
> }
> EXPORT_SYMBOL_GPL(nfs_open_local_fh);
> diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> index c16671135d17..9a62b4da89bb 100644
> --- a/fs/nfsd/filecache.c
> +++ b/fs/nfsd/filecache.c
> @@ -391,19 +391,19 @@ nfsd_file_put(struct nfsd_file *nf)
> }
>
> /**
> - * nfsd_file_put_local - put the reference to nfsd_file and local nfsd_serv
> - * @nf: nfsd_file of which to put the references
> + * nfsd_file_put_local - put nfsd_file reference and arm nfsd_serv_put in caller
> + * @nf: nfsd_file of which to put the reference
> *
> - * First put the reference of the nfsd_file and then put the
> - * reference to the associated nn->nfsd_serv.
> + * First save the associated net to return to caller, then put
> + * the reference of the nfsd_file.
> */
> -void
> -nfsd_file_put_local(struct nfsd_file *nf) __must_hold(rcu)
> +struct net *
> +nfsd_file_put_local(struct nfsd_file *nf)
> {
> struct net *net = nf->nf_net;
>
> nfsd_file_put(nf);
> - nfsd_serv_put(net);
> + return net;
> }
>
> /**
> diff --git a/fs/nfsd/filecache.h b/fs/nfsd/filecache.h
> index cadf3c2689c4..d5db6b34ba30 100644
> --- a/fs/nfsd/filecache.h
> +++ b/fs/nfsd/filecache.h
> @@ -55,7 +55,7 @@ void nfsd_file_cache_shutdown(void);
> int nfsd_file_cache_start_net(struct net *net);
> void nfsd_file_cache_shutdown_net(struct net *net);
> void nfsd_file_put(struct nfsd_file *nf);
> -void nfsd_file_put_local(struct nfsd_file *nf);
> +struct net *nfsd_file_put_local(struct nfsd_file *nf);
> struct nfsd_file *nfsd_file_get(struct nfsd_file *nf);
> struct file *nfsd_file_file(struct nfsd_file *nf);
> void nfsd_file_close_inode_sync(struct inode *inode);
> diff --git a/include/linux/nfslocalio.h b/include/linux/nfslocalio.h
> index 3982fea79919..9202f4b24343 100644
> --- a/include/linux/nfslocalio.h
> +++ b/include/linux/nfslocalio.h
> @@ -55,7 +55,7 @@ struct nfsd_localio_operations {
> const struct cred *,
> const struct nfs_fh *,
> const fmode_t);
> - void (*nfsd_file_put_local)(struct nfsd_file *);
> + struct net *(*nfsd_file_put_local)(struct nfsd_file *);
> struct file *(*nfsd_file_file)(struct nfsd_file *);
> } ____cacheline_aligned;
>
> @@ -66,7 +66,7 @@ struct nfsd_file *nfs_open_local_fh(nfs_uuid_t *,
> struct rpc_clnt *, const struct cred *,
> const struct nfs_fh *, const fmode_t);
>
> -static inline void nfs_to_nfsd_file_put_local(struct nfsd_file *localio)
> +static inline void nfs_to_nfsd_net_put(struct net *net)
> {
> /*
> * Once reference to nfsd_serv is dropped, NFSD could be
> @@ -74,10 +74,22 @@ static inline void nfs_to_nfsd_file_put_local(struct nfsd_file *localio)
> * by always taking RCU.
> */
> rcu_read_lock();
> - nfs_to->nfsd_file_put_local(localio);
> + nfs_to->nfsd_serv_put(net);
> rcu_read_unlock();
> }
>
> +static inline void nfs_to_nfsd_file_put_local(struct nfsd_file *localio)
> +{
> + /*
> + * Must not hold RCU otherwise nfsd_file_put() can easily trigger:
> + * "Voluntary context switch within RCU read-side critical section!"
> + * by scheduling deep in underlying filesystem (e.g. XFS).
> + */
> + struct net *net = nfs_to->nfsd_file_put_local(localio);
> +
> + nfs_to_nfsd_net_put(net);
> +}
> +
> #else /* CONFIG_NFS_LOCALIO */
> static inline void nfsd_localio_ops_init(void)
> {

I think this probably needs to go into v6.12 (or very early into v6.13
and backported). It should also probably get:

Fixes: 65f2a5c36635 ("nfs_common: fix race in NFS calls to nfsd_file_put_local() and nfsd_serv_put()")

You can also add:

Reviewed-by: Jeff Layton <jlayton@kernel.org>