In order to avoid an ABBA lock ordering issue, the write code must
unlock and release the nfs_page _before_ it calls end_page_writeback.
Since the last release of the nfs_page will trigger a call to put
the open_context, we need to ensure that something else holds a
reference to the open context until we're done with the
end_page_writeback so that we don't end up calling iput while we're
still holding a PG_writeback lock.
We can fix this by changing nfs_writedata_release to put the open
context after we have processed all the page data.
The read code does not suffer from the same problem, since it doesn't
hold a lock on the nfs_page, so it just calls nfs_release_request after
unlocking the page itself. However, for symmetry reasons, we make the
same change to nfs_readdata_release.
Signed-off-by: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
Cc: Fred Isaman <iisaman@xxxxxxxxxx>
---
fs/nfs/read.c | 3 ++-
fs/nfs/write.c | 13 ++++++++++++-
2 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/fs/nfs/read.c b/fs/nfs/read.c
index f23cf25..dec47e5 100644
--- a/fs/nfs/read.c
+++ b/fs/nfs/read.c
@@ -87,8 +87,8 @@ void nfs_readdata_release(struct nfs_read_data *rdata)
{
struct nfs_pgio_header *hdr = rdata->header;
struct nfs_read_header *read_header = container_of(hdr, struct nfs_read_header, header);
+ struct nfs_open_context *ctx = rdata->args.context;
- put_nfs_open_context(rdata->args.context);
if (rdata->pages.pagevec != rdata->pages.page_array)
kfree(rdata->pages.pagevec);
if (rdata != &read_header->rpc_data)
@@ -97,6 +97,7 @@ void nfs_readdata_release(struct nfs_read_data *rdata)
rdata->header = NULL;
if (atomic_dec_and_test(&hdr->refcnt))
hdr->completion_ops->completion(hdr);
+ put_nfs_open_context(ctx);
}
static
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 6f263da..69825f7 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -119,8 +119,8 @@ void nfs_writedata_release(struct nfs_write_data *wdata)
{
struct nfs_pgio_header *hdr = wdata->header;
struct nfs_write_header *write_header = container_of(hdr, struct nfs_write_header, header);
+ struct nfs_open_context *ctx = wdata->args.context;
- put_nfs_open_context(wdata->args.context);
if (wdata->pages.pagevec != wdata->pages.page_array)
kfree(wdata->pages.pagevec);
if (wdata != &write_header->rpc_data)
@@ -129,6 +129,10 @@ void nfs_writedata_release(struct nfs_write_data *wdata)
wdata->header = NULL;
if (atomic_dec_and_test(&hdr->refcnt))
hdr->completion_ops->completion(hdr);
+ /* Note: put the open context after processing all the
+ * page data in order to avoid a deadlock in nfs_write_completion.
+ */
+ put_nfs_open_context(ctx);
}
static void nfs_context_set_write_error(struct nfs_open_context *ctx, int error)
@@ -597,6 +601,13 @@ int nfs_write_need_commit(struct nfs_write_data *data)
#endif
+/*
+ * nfs_write_completion - process the results of the write RPC calls
+ *
+ * Note: this function assumes that the caller is holding a reference
+ * to the nfs_open_context in order to avoid a deadlock when calling
+ * nfs_end_page_writeback after nfs_unlock_request.
+ */
static void nfs_write_completion(struct nfs_pgio_header *hdr)
{
struct nfs_commit_info cinfo;
--
1.7.7.6
--
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