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authorTrond Myklebust <Trond.Myklebust@netapp.com>2007-05-20 10:18:27 -0400
committerTrond Myklebust <Trond.Myklebust@netapp.com>2007-05-24 10:44:20 -0400
commit7fe7f8487ae742239dd8c66596e2311c30d057d1 (patch)
treec506bd7dcacc9d5b25b3295bd1f327e534532c54
parent585a2858b970cb6e2e5ca4877eefd18b4dba8ed4 (diff)
NFS: Avoid a deadlock situation on write
When processes are allowed to attempt to lock a non-contiguous range of nfs write requests, it is possible for generic_writepages to 'wrap round' the address space, and call writepage() on a request that is already locked by the same process. We avoid the deadlock by checking if the page index is contiguous with the list of nfs write requests that is already held in our nfs_pageio_descriptor prior to attempting to lock a new request. Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
-rw-r--r--fs/nfs/pagelist.c20
-rw-r--r--fs/nfs/write.c6
-rw-r--r--include/linux/nfs_page.h1
3 files changed, 25 insertions, 2 deletions
diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index cbdd1c6aaa94..c5bb51a29e80 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -355,6 +355,26 @@ void nfs_pageio_complete(struct nfs_pageio_descriptor *desc)
nfs_pageio_doio(desc);
}
+/**
+ * nfs_pageio_cond_complete - Conditional I/O completion
+ * @desc: pointer to io descriptor
+ * @index: page index
+ *
+ * It is important to ensure that processes don't try to take locks
+ * on non-contiguous ranges of pages as that might deadlock. This
+ * function should be called before attempting to wait on a locked
+ * nfs_page. It will complete the I/O if the page index 'index'
+ * is not contiguous with the existing list of pages in 'desc'.
+ */
+void nfs_pageio_cond_complete(struct nfs_pageio_descriptor *desc, pgoff_t index)
+{
+ if (!list_empty(&desc->pg_list)) {
+ struct nfs_page *prev = nfs_list_entry(desc->pg_list.prev);
+ if (index != prev->wb_index + 1)
+ nfs_pageio_doio(desc);
+ }
+}
+
#define NFS_SCAN_MAXENTRIES 16
/**
* nfs_scan_list - Scan a list for matching requests
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index b084c03ce493..af344a158e01 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -273,8 +273,6 @@ static int nfs_page_async_flush(struct nfs_pageio_descriptor *pgio,
* request as dirty (in which case we don't care).
*/
spin_unlock(req_lock);
- /* Prevent deadlock! */
- nfs_pageio_complete(pgio);
ret = nfs_wait_on_request(req);
nfs_release_request(req);
if (ret != 0)
@@ -321,6 +319,8 @@ static int nfs_writepage_locked(struct page *page, struct writeback_control *wbc
pgio = &mypgio;
}
+ nfs_pageio_cond_complete(pgio, page->index);
+
err = nfs_page_async_flush(pgio, page);
if (err <= 0)
goto out;
@@ -329,6 +329,8 @@ static int nfs_writepage_locked(struct page *page, struct writeback_control *wbc
if (!offset)
goto out;
+ nfs_pageio_cond_complete(pgio, page->index);
+
ctx = nfs_find_open_context(inode, NULL, FMODE_WRITE);
if (ctx == NULL) {
err = -EBADF;
diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
index 41afab6b5f09..bd193af80162 100644
--- a/include/linux/nfs_page.h
+++ b/include/linux/nfs_page.h
@@ -81,6 +81,7 @@ extern void nfs_pageio_init(struct nfs_pageio_descriptor *desc,
extern int nfs_pageio_add_request(struct nfs_pageio_descriptor *,
struct nfs_page *);
extern void nfs_pageio_complete(struct nfs_pageio_descriptor *desc);
+extern void nfs_pageio_cond_complete(struct nfs_pageio_descriptor *, pgoff_t);
extern int nfs_wait_on_request(struct nfs_page *);
extern void nfs_unlock_request(struct nfs_page *req);
extern int nfs_set_page_writeback_locked(struct nfs_page *req);