[PATCH 5.16 127/285] NFSv4: Protect the state recovery thread against direct reclaim

Greg Kroah-Hartman
2022-04-12T07:55:18Z

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

[ 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@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/nfs/nfs4state.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index 499bef9fe118..94f1876afab2 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>

@@ -2560,9 +2561,17 @@ static void nfs4_layoutreturn_any_run(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 {
trace_nfs4_state_mgr(clp);
@@ -2657,6 +2666,7 @@ 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);

@@ -2674,6 +2684,7 @@ 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;

@@ -2686,6 +2697,7 @@ 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