From: Trond Myklebust <trond.myklebust@hammerspace.com>

Date: Sat, 29 Jan 2022 13:32:45 -0500

Subject: [PATCH] NFSv4: Protect the state recovery thread against direct

 reclaim

Git-commit: 3e17898aca293a24dae757a440a50aa63ca29671

Patch-mainline: v5.18

References: git-fixes

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@hammerspace.com>

Acked-by: NeilBrown <neilb@suse.com>

---

 fs/nfs/nfs4state.c |   12 ++++++++++++

 1 file changed, 12 insertions(+)

--- 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>

@@ -2576,9 +2577,17 @@ static void nfs4_layoutreturn_any_run(st

 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 {

 		trace_nfs4_state_mgr(clp);

@@ -2673,6 +2682,7 @@ static void nfs4_state_manager(struct nf

 			clear_bit(NFS4CLNT_RECLAIM_NOGRACE, &clp->cl_state);

 		}

+		memalloc_nofs_restore(memflags);

 		nfs4_end_drain_session(clp);

 		nfs4_clear_state_manager_bit(clp);

@@ -2690,6 +2700,7 @@ static void nfs4_state_manager(struct nf

 			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;

@@ -2702,6 +2713,7 @@ out_error:

 			clp->cl_hostname, -status);

 	ssleep(1);

 out_drain:

+	memalloc_nofs_restore(memflags);

 	nfs4_end_drain_session(clp);

 	nfs4_clear_state_manager_bit(clp);

 }