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authorTrond Myklebust <Trond.Myklebust@netapp.com>2012-05-09 14:30:35 -0400
committerTrond Myklebust <Trond.Myklebust@netapp.com>2012-05-09 15:16:07 -0400
commit3aff4ebb95b20ad8db2c1447e8c52097d89af5a7 (patch)
treead56aceafbcbd0650e71e029ffa138eedffd33ba
parentdc327ed4cd320be689596365372a3683208c3ba0 (diff)
downloadlinux-3aff4ebb95b20ad8db2c1447e8c52097d89af5a7.tar.gz
NFS: Prevent a deadlock in the new writeback code
We have to unlock the nfs_page before we call nfs_end_page_writeback to avoid races with functions that expect the page to be unlocked when PG_locked and PG_writeback are not set. The problem is that nfs_unlock_request also releases the nfs_page, causing a deadlock if the release of the nfs_open_context triggers an iput() while the PG_writeback flag is still set... The solution is to separate the unlocking and release of the nfs_page, so that we can do the former before nfs_end_page_writeback and the latter after. Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com> Cc: Fred Isaman <iisaman@netapp.com>
-rw-r--r--fs/nfs/pagelist.c12
-rw-r--r--fs/nfs/write.c6
-rw-r--r--include/linux/nfs_page.h1
3 files changed, 15 insertions, 4 deletions
diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index 33a21ca9b84b..69146f386989 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -128,10 +128,10 @@ nfs_create_request(struct nfs_open_context *ctx, struct inode *inode,
}
/**
- * nfs_unlock_request - Unlock request and wake up sleepers.
+ * nfs_unlock_request_dont_release - Unlock request and wake up sleepers.
* @req:
*/
-void nfs_unlock_request(struct nfs_page *req)
+void nfs_unlock_request_dont_release(struct nfs_page *req)
{
if (!NFS_WBACK_BUSY(req)) {
printk(KERN_ERR "NFS: Invalid unlock attempted\n");
@@ -141,6 +141,14 @@ void nfs_unlock_request(struct nfs_page *req)
clear_bit(PG_BUSY, &req->wb_flags);
smp_mb__after_clear_bit();
wake_up_bit(&req->wb_flags, PG_BUSY);
+}
+
+/**
+ * nfs_unlock_request - Unlock request and release the nfs_page
+ */
+void nfs_unlock_request(struct nfs_page *req)
+{
+ nfs_unlock_request_dont_release(req);
nfs_release_request(req);
}
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 6f263daac748..fd36b31ee72e 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -628,8 +628,9 @@ static void nfs_write_completion(struct nfs_pgio_header *hdr)
remove_req:
nfs_inode_remove_request(req);
next:
- nfs_unlock_request(req);
+ nfs_unlock_request_dont_release(req);
nfs_end_page_writeback(page);
+ nfs_release_request(req);
}
out:
hdr->release(hdr);
@@ -1042,8 +1043,9 @@ static void nfs_redirty_request(struct nfs_page *req)
struct page *page = req->wb_page;
nfs_mark_request_dirty(req);
- nfs_unlock_request(req);
+ nfs_unlock_request_dont_release(req);
nfs_end_page_writeback(page);
+ nfs_release_request(req);
}
static void nfs_async_write_error(struct list_head *head)
diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
index f9ee9eba7f88..ef7504215446 100644
--- a/include/linux/nfs_page.h
+++ b/include/linux/nfs_page.h
@@ -96,6 +96,7 @@ extern bool nfs_generic_pg_test(struct nfs_pageio_descriptor *desc,
struct nfs_page *req);
extern int nfs_wait_on_request(struct nfs_page *);
extern void nfs_unlock_request(struct nfs_page *req);
+extern void nfs_unlock_request_dont_release(struct nfs_page *req);
/*
* Lock the page of an asynchronous request without getting a new reference