linux-kernel - [RFC 8/9] gfs2: Add LM_FLAG

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Date:   Mon, 31 May 2021 19:01:22 +0200
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andreas Gruenbacher <agruenba@...hat.com>,
        cluster-devel@...hat.com, linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jan Kara <jack@...e.cz>, Matthew Wilcox <willy@...radead.org>
Subject: [RFC 8/9] gfs2: Add LM_FLAG_OUTER glock holder flag

When a glock holder has the LM_FLAG_OUTER flag set, we set the
current_holds_glock() flag upon taking the lock.  With that, we
can recognize when trying to take an "inner" glock, and react
accordingly.

Signed-off-by: Andreas Gruenbacher <agruenba@...hat.com>
---
 fs/gfs2/glock.c | 12 ++++++++++++
 fs/gfs2/glock.h | 13 ++++++++++---
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index d9cb261f55b0..f6cae2ee1c83 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1427,6 +1427,11 @@ int gfs2_glock_nq(struct gfs2_holder *gh)
 	if (glock_blocked_by_withdraw(gl) && !(gh->gh_flags & LM_FLAG_NOEXP))
 		return -EIO;
 
+	if (gh->gh_flags & LM_FLAG_OUTER) {
+		BUG_ON(current_holds_glock());
+		set_current_holds_glock(true);
+	}
+
 	if (test_bit(GLF_LRU, &gl->gl_flags))
 		gfs2_glock_remove_from_lru(gl);
 
@@ -1514,6 +1519,11 @@ void gfs2_glock_dq(struct gfs2_holder *gh)
 		__gfs2_glock_queue_work(gl, delay);
 	}
 	spin_unlock(&gl->gl_lockref.lock);
+
+	if (gh->gh_flags & LM_FLAG_OUTER) {
+		BUG_ON(!current_holds_glock());
+		set_current_holds_glock(false);
+	}
 }
 
 void gfs2_glock_dq_wait(struct gfs2_holder *gh)
@@ -2068,6 +2078,8 @@ static const char *hflags2str(char *buf, u16 flags, unsigned long iflags)
 		*p++ = 'p';
 	if (flags & LM_FLAG_NODE_SCOPE)
 		*p++ = 'n';
+	if (flags & LM_FLAG_OUTER)
+		*p++ = 'o';
 	if (flags & GL_ASYNC)
 		*p++ = 'a';
 	if (flags & GL_EXACT)
diff --git a/fs/gfs2/glock.h b/fs/gfs2/glock.h
index f0ef6fd24ba4..8b145269fb14 100644
--- a/fs/gfs2/glock.h
+++ b/fs/gfs2/glock.h
@@ -94,6 +94,12 @@ static inline bool gfs2_holder_is_compatible(struct gfs2_holder *gh, int state)
  * This holder agrees to share the lock within this node. In other words,
  * the glock is held in EX mode according to DLM, but local holders on the
  * same node can share it.
+ *
+ * LM_FLAG_OUTER
+ * Use set_current_holds_glock() to indicate when the current task is holding
+ * this "upper" glock, and current_holds_glock() to detect when the current
+ * task is trying to take another glock.  Used to prevent deadlocks involving
+ * the inode glock during page faults.
  */
 
 #define LM_FLAG_TRY		0x0001
@@ -102,9 +108,10 @@ static inline bool gfs2_holder_is_compatible(struct gfs2_holder *gh, int state)
 #define LM_FLAG_ANY		0x0008
 #define LM_FLAG_PRIORITY	0x0010
 #define LM_FLAG_NODE_SCOPE	0x0020
-#define GL_ASYNC		0x0040
-#define GL_EXACT		0x0080
-#define GL_SKIP			0x0100
+#define LM_FLAG_OUTER		0x0040
+#define GL_ASYNC		0x0080
+#define GL_EXACT		0x0100
+#define GL_SKIP			0x0200
 #define GL_NOCACHE		0x0400
   
 /*
-- 
2.26.3