[PATCH 02 of 16] avoid oom deadlock in nfs_create_request

[Andrea Arcangeli <andrea@suse.de>]

# HG changeset patch
# User Andrea Arcangeli <andrea@suse.de>
# Date 1181332960 -7200
# Node ID d64cb81222748354bf5b16258197217465f35aeb
# Parent  8e38f7656968417dfee09fbb6450a8f1e70f8b21
avoid oom deadlock in nfs_create_request

When sigkill is pending after the oom killer set TIF_MEMDIE, the task
must go away or the VM will malfunction.

Signed-off-by: Andrea Arcangeli <andrea@suse.de>

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -61,16 +61,20 @@ nfs_create_request(struct nfs_open_conte
 	struct nfs_server *server = NFS_SERVER(inode);
 	struct nfs_page		*req;
 
-	for (;;) {
-		/* try to allocate the request struct */
-		req = nfs_page_alloc();
-		if (req != NULL)
-			break;
-
-		if (signalled() && (server->flags & NFS_MOUNT_INTR))
-			return ERR_PTR(-ERESTARTSYS);
-		yield();
-	}
+	/* try to allocate the request struct */
+	req = nfs_page_alloc();
+	if (unlikely(!req)) {
+		/*
+		 * -ENOMEM will be returned only when TIF_MEMDIE is set
+		 * so userland shouldn't risk to get confused by a new
+		 * unhandled ENOMEM errno.
+		 */
+		WARN_ON(!test_thread_flag(TIF_MEMDIE));
+		return ERR_PTR(-ENOMEM);
+	}
+
+	if (signalled() && (server->flags & NFS_MOUNT_INTR))
+		return ERR_PTR(-ERESTARTSYS);
 
 	/* Initialize the request struct. Initially, we assume a
 	 * long write-back delay. This will be adjusted in

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