[PATCH 5.4 410/475] NFSv4: Protect the state recovery thread against direct reclaim

[Greg Kroah-Hartman]

From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>

[ Upstream commit 3e17898aca293a24dae757a440a50aa63ca29671 ]

If memory allocation triggers a direct reclaim from the state recovery
thread, then we can deadlock. Use memalloc_nofs_save/restore to ensure
that doesn't happen.

Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/nfs/nfs4state.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index aa2caba38a01..1d2b81a233bb 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -49,6 +49,7 @@
 #include <linux/workqueue.h>
 #include <linux/bitops.h>
 #include <linux/jiffies.h>
+#include <linux/sched/mm.h>
 
 #include <linux/sunrpc/clnt.h>
 
@@ -2504,9 +2505,17 @@ static int nfs4_bind_conn_to_session(struct nfs_client *clp)
 
 static void nfs4_state_manager(struct nfs_client *clp)
 {
+	unsigned int memflags;
 	int status = 0;
 	const char *section = "", *section_sep = "";
 
+	/*
+	 * State recovery can deadlock if the direct reclaim code tries
+	 * start NFS writeback. So ensure memory allocations are all
+	 * GFP_NOFS.
+	 */
+	memflags = memalloc_nofs_save();
+
 	/* Ensure exclusive access to NFSv4 state */
 	do {
 		clear_bit(NFS4CLNT_RUN_MANAGER, &clp->cl_state);
@@ -2600,6 +2609,7 @@ static void nfs4_state_manager(struct nfs_client *clp)
 			clear_bit(NFS4CLNT_RECLAIM_NOGRACE, &clp->cl_state);
 		}
 
+		memalloc_nofs_restore(memflags);
 		nfs4_end_drain_session(clp);
 		nfs4_clear_state_manager_bit(clp);
 
@@ -2616,6 +2626,7 @@ static void nfs4_state_manager(struct nfs_client *clp)
 			return;
 		if (test_and_set_bit(NFS4CLNT_MANAGER_RUNNING, &clp->cl_state) != 0)
 			return;
+		memflags = memalloc_nofs_save();
 	} while (refcount_read(&clp->cl_count) > 1 && !signalled());
 	goto out_drain;
 
@@ -2627,6 +2638,7 @@ static void nfs4_state_manager(struct nfs_client *clp)
 			clp->cl_hostname, -status);
 	ssleep(1);
 out_drain:
+	memalloc_nofs_restore(memflags);
 	nfs4_end_drain_session(clp);
 	nfs4_clear_state_manager_bit(clp);
 }
-- 
2.35.1