Re: [PATCH 11/24] pnfs_submit: expose pnfs_update_layout, put_lseg, and get_lseg functions

Boaz Harrosh
2010-06-09T18:58:24Z

On 06/08/2010 07:19 AM, Fred Isaman wrote:
> These will be used in the generic code. Set so they will compile away to
> nothing if CONFIG_NFS_V4_1 not set.
>
> This requires kref_put to be under lock. See rule 3 of Documentation/kref.txt
>

I don't see "rule 3" in here. Please explain how?

BTW: Even "rule 3" bad example with the lists, have a counter example in the Kernel
with lists and searches that kref_put/get lockless. (By each element refing
it's pear and taking the reference of the first one before search)

> Signed-off-by: Fred Isaman <iisaman@netapp.com>
> ---
> fs/nfs/pnfs.c | 45 ++++++++++++++++++++++++++++++++-------------
> fs/nfs/pnfs.h | 44 +++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 75 insertions(+), 14 deletions(-)
>
> diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
> index 836cb0f..a74a4b6 100644
> --- a/fs/nfs/pnfs.c
> +++ b/fs/nfs/pnfs.c
> @@ -436,7 +436,25 @@ destroy_lseg(struct kref *kref)
> PNFS_LD_IO_OPS(lseg->layout)->free_lseg(lseg);
> }
>
> -static inline void
> +static void
> +put_lseg_locked(struct pnfs_layout_segment *lseg)
> +{
> + bool do_wake_up;
> + struct nfs_inode *nfsi;
> +
> + if (!lseg)
> + return;
> +
> + dprintk("%s: lseg %p ref %d valid %d\n", __func__, lseg,
> + atomic_read(&lseg->kref.refcount), lseg->valid);
> + do_wake_up = !lseg->valid;
> + nfsi = PNFS_NFS_INODE(lseg->layout);
> + kref_put(&lseg->kref, destroy_lseg);
> + if (do_wake_up)
> + wake_up(&nfsi->lo_waitq);
> +}
> +
> +void
> put_lseg(struct pnfs_layout_segment *lseg)
> {
> bool do_wake_up;
> @@ -449,7 +467,9 @@ put_lseg(struct pnfs_layout_segment *lseg)
> atomic_read(&lseg->kref.refcount), lseg->valid);
> do_wake_up = !lseg->valid;
> nfsi = PNFS_NFS_INODE(lseg->layout);
> + lock_current_layout(nfsi);
> kref_put(&lseg->kref, destroy_lseg);
> + unlock_current_layout(nfsi);
> if (do_wake_up)
> wake_up(&nfsi->lo_waitq);
> }
> @@ -674,7 +694,7 @@ pnfs_free_layout(struct pnfs_layout_type *lo,
> lseg, lseg->range.iomode, lseg->range.offset,
> lseg->range.length);
> list_del(&lseg->fi_list);
> - put_lseg(lseg);
> + put_lseg_locked(lseg);
> }
>
> dprintk("%s:Return\n", __func__);
> @@ -1033,7 +1053,7 @@ pnfs_has_layout(struct pnfs_layout_type *lo,
> (lseg->valid || !only_valid)) {
> ret = lseg;
> if (take_ref)
> - kref_get(&ret->kref);
> + get_lseg(ret);
> break;
> }
> if (cmp_layout(range, &lseg->range) > 0)
> @@ -1053,7 +1073,7 @@ pnfs_has_layout(struct pnfs_layout_type *lo,
> * returned to the caller.
> */
> int
> -pnfs_update_layout(struct inode *ino,
> +_pnfs_update_layout(struct inode *ino,
> struct nfs_open_context *ctx,
> u64 count,
> loff_t pos,
> @@ -1085,8 +1105,7 @@ pnfs_update_layout(struct inode *ino,
> lseg = pnfs_has_layout(lo, &arg, take_ref, !take_ref);
> if (lseg && !lseg->valid) {
> if (take_ref)
> - put_lseg(lseg);
> -
> + put_lseg_locked(lseg);
> /* someone is cleaning the layout */
> lseg = NULL;
> result = -EAGAIN;
> @@ -1262,7 +1281,7 @@ pnfs_layout_process(struct nfs4_pnfs_layoutget *lgp)
> init_lseg(lo, lseg);
> lseg->range = res->lseg;
> if (lgp->lsegpp) {
> - kref_get(&lseg->kref);
> + get_lseg(lseg);
> *lgp->lsegpp = lseg;
> }
>
> @@ -1380,7 +1399,7 @@ pnfs_pageio_init_read(struct nfs_pageio_descriptor *pgio,
> readahead_range(inode, pages, &loff, &count);
>
> if (count > 0) {
> - status = pnfs_update_layout(inode, ctx, count,
> + status = _pnfs_update_layout(inode, ctx, count,
> loff, IOMODE_READ, NULL);
> dprintk("%s virt update returned %d\n", __func__, status);
> if (status != 0)
> @@ -1438,7 +1457,7 @@ pnfs_update_layout_commit(struct inode *inode,
> if (start == 0 && count == 0)
> count = NFS4_MAX_UINT64;
>
> - status = pnfs_update_layout(inode, nfs_page->wb_context,
> + status = _pnfs_update_layout(inode, nfs_page->wb_context,
> count,
> start,
> IOMODE_RW,
> @@ -1538,7 +1557,7 @@ pnfs_file_write(struct file *filp, const char __user *buf, size_t count,
> goto out;
>
> /* Retrieve and set layout if not allready cached */
> - status = pnfs_update_layout(inode,
> + status = _pnfs_update_layout(inode,
> context,
> count,
> *pos,
> @@ -1580,7 +1599,7 @@ pnfs_writepages(struct nfs_write_data *wdata, int how)
> args->offset);
>
> /* Retrieve and set layout if not allready cached */
> - status = pnfs_update_layout(inode,
> + status = _pnfs_update_layout(inode,
> args->context,
> args->count,
> args->offset,
> @@ -1681,7 +1700,7 @@ pnfs_readpages(struct nfs_read_data *rdata)
> args->offset);
>
> /* Retrieve and set layout if not allready cached */
> - status = pnfs_update_layout(inode,
> + status = _pnfs_update_layout(inode,
> args->context,
> args->count,
> args->offset,
> @@ -1845,7 +1864,7 @@ pnfs_commit(struct nfs_write_data *data, int sync)
> new one. If it was recalled we better commit the data first
> before returning it, otherwise the data needs to be rewritten,
> either with a new layout or to the MDS */
> - result = pnfs_update_layout(data->inode,
> + result = _pnfs_update_layout(data->inode,
> NULL,
> count,
> first->wb_offset,
> diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
> index 214d567..6326ed5 100644
> --- a/fs/nfs/pnfs.h
> +++ b/fs/nfs/pnfs.h
> @@ -31,7 +31,8 @@ extern int pnfs4_proc_layoutreturn(struct nfs4_pnfs_layoutreturn *lrp, bool wait
> /* pnfs.c */
> extern const nfs4_stateid zero_stateid;
>
> -int pnfs_update_layout(struct inode *ino, struct nfs_open_context *ctx,
> +void put_lseg(struct pnfs_layout_segment *lseg);
> +int _pnfs_update_layout(struct inode *ino, struct nfs_open_context *ctx,
> u64 count, loff_t pos, enum pnfs_iomode access_type,
> struct pnfs_layout_segment **lsegpp);
>
> @@ -81,6 +82,12 @@ static inline int lo_fail_bit(u32 iomode)
> NFS_INO_RW_LAYOUT_FAILED : NFS_INO_RO_LAYOUT_FAILED;
> }
>
> +static inline void get_lseg(struct pnfs_layout_segment *lseg)
> +{
> + if (lseg)

Really? That in my experience is a shoot in the foot.

I don't believe any code that decided to get an lseg could get there without one.
if so I want to crash.

>From all instances of get_lseg in this patch they already ask.

> + kref_get(&lseg->kref);
> +}
> +
> /* Return true if a layout driver is being used for this mountpoint */
> static inline int pnfs_enabled_sb(struct nfs_server *nfss)
> {
> @@ -170,6 +177,23 @@ static inline int pnfs_return_layout(struct inode *ino,
> return 0;
> }
>
> +static inline int pnfs_update_layout(struct inode *ino,
> + struct nfs_open_context *ctx,
> + u64 count, loff_t pos, enum pnfs_iomode access_type,
> + struct pnfs_layout_segment **lsegpp)
> +{
> + struct nfs_server *nfss = NFS_SERVER(ino);
> +
> + if (pnfs_enabled_sb(nfss))
> + return _pnfs_update_layout(ino, ctx, count, pos,
> + access_type, lsegpp);
> + else {
> + if (lsegpp)
> + *lsegpp = NULL;
> + return 0;
> + }
> +}
> +
> static inline int pnfs_get_write_status(struct nfs_write_data *data)
> {
> return data->pdata.pnfs_error;
> @@ -190,6 +214,24 @@ static inline int pnfs_use_rpc(struct nfs_server *nfss)
>
> #else /* CONFIG_NFS_V4_1 */
>
> +static inline void get_lseg(struct pnfs_layout_segment *lseg)
> +{
> +}
> +
> +static inline void put_lseg(struct pnfs_layout_segment *lseg)
> +{
> +}
> +
> +static inline int
> +pnfs_update_layout(struct inode *ino, struct nfs_open_context *ctx,
> + u64 count, loff_t pos, enum pnfs_iomode access_type,
> + struct pnfs_layout_segment **lsegpp)
> +{
> + if (lsegpp)
> + *lsegpp = NULL;
> + return 0;
> +}
> +
> static inline enum pnfs_try_status
> pnfs_try_to_read_data(struct nfs_read_data *data,
> const struct rpc_call_ops *call_ops)

Comments aside. Good needed stuff
Boaz