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NFSv4.2: Rework scratch handling for READ_PLUS (again) 

I found that the read code might send multiple requests using the same
nfs_pgio_header, but nfs4_proc_read_setup() is only called once. This is
how we ended up occasionally double-freeing the scratch buffer, but also
means we set a NULL pointer but non-zero length to the xdr scratch
buffer. This results in an oops the first time decoding needs to copy
something to scratch, which frequently happens when decoding READ_PLUS
hole segments.

I fix this by moving scratch handling into the pageio read code. I
provide a function to allocate scratch space for decoding read replies,
and free the scratch buffer when the nfs_pgio_header is freed.

Fixes: fbd2a05f29 (NFSv4.2: Rework scratch handling for READ_PLUS)
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
This commit is contained in:
Anna Schumaker 2023-06-09 15:26:25 -04:00
parent 8d18f6c5bb
commit 303a780520
5 changed files with 14 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
fs/nfs/internal.h
View File

@ -493,6 +493,7 @@ extern const struct nfs_pgio_completion_ops nfs_async_read_completion_ops;
extern void nfs_pageio_init_read(struct nfs_pageio_descriptor *pgio,
struct inode *inode, bool force_mds,
const struct nfs_pgio_completion_ops *compl_ops);
extern bool nfs_read_alloc_scratch(struct nfs_pgio_header *hdr, size_t size);
extern int nfs_read_add_folio(struct nfs_pageio_descriptor *pgio,
struct nfs_open_context *ctx,
struct folio *folio);

1
fs/nfs/nfs42.h
View File

@ -13,6 +13,7 @@
* more? Need to consider not to pre-alloc too much for a compound.
*/
#define PNFS_LAYOUTSTATS_MAXDEV (4)
#define READ_PLUS_SCRATCH_SIZE (16)
/* nfs4.2proc.c */
#ifdef CONFIG_NFS_V4_2

2
fs/nfs/nfs42xdr.c
View File

@ -1433,7 +1433,7 @@ static int nfs4_xdr_dec_read_plus(struct rpc_rqst *rqstp,
struct compound_hdr hdr;
int status;
xdr_set_scratch_buffer(xdr, res->scratch, sizeof(res->scratch));
xdr_set_scratch_buffer(xdr, res->scratch, READ_PLUS_SCRATCH_SIZE);
status = decode_compound_hdr(xdr, &hdr);
if (status)

13
fs/nfs/nfs4proc.c
View File

@ -5438,18 +5438,8 @@ static bool nfs4_read_plus_not_supported(struct rpc_task *task,
return false;
}
static inline void nfs4_read_plus_scratch_free(struct nfs_pgio_header *hdr)
{
if (hdr->res.scratch) {
kfree(hdr->res.scratch);
hdr->res.scratch = NULL;
}
}
static int nfs4_read_done(struct rpc_task *task, struct nfs_pgio_header *hdr)
{
nfs4_read_plus_scratch_free(hdr);
if (!nfs4_sequence_done(task, &hdr->res.seq_res))
return -EAGAIN;
if (nfs4_read_stateid_changed(task, &hdr->args))
@ -5469,8 +5459,7 @@ static bool nfs42_read_plus_support(struct nfs_pgio_header *hdr,
/* Note: We don't use READ_PLUS with pNFS yet */
if (nfs_server_capable(hdr->inode, NFS_CAP_READ_PLUS) && !hdr->ds_clp) {
msg->rpc_proc = &nfs4_procedures[NFSPROC4_CLNT_READ_PLUS];
hdr->res.scratch = kmalloc(32, GFP_KERNEL);
return hdr->res.scratch != NULL;
return nfs_read_alloc_scratch(hdr, READ_PLUS_SCRATCH_SIZE);
}
return false;
}

10
fs/nfs/read.c
View File

@ -47,6 +47,8 @@ static struct nfs_pgio_header *nfs_readhdr_alloc(void)
static void nfs_readhdr_free(struct nfs_pgio_header *rhdr)
{
if (rhdr->res.scratch != NULL)
kfree(rhdr->res.scratch);
kmem_cache_free(nfs_rdata_cachep, rhdr);
}
@ -108,6 +110,14 @@ void nfs_pageio_reset_read_mds(struct nfs_pageio_descriptor *pgio)
}
EXPORT_SYMBOL_GPL(nfs_pageio_reset_read_mds);
bool nfs_read_alloc_scratch(struct nfs_pgio_header *hdr, size_t size)
{
WARN_ON(hdr->res.scratch != NULL);
hdr->res.scratch = kmalloc(size, GFP_KERNEL);
return hdr->res.scratch != NULL;
}
EXPORT_SYMBOL_GPL(nfs_read_alloc_scratch);
static void nfs_readpage_release(struct nfs_page *req, int error)
{
struct folio *folio = nfs_page_to_folio(req);