linux-kernel - [RFC 7/9] gfs2: Encode glock holding and retry flags in journal

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Message-Id: <20210531170123.243771-8-agruenba@redhat.com>
Date:   Mon, 31 May 2021 19:01:21 +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 7/9] gfs2: Encode glock holding and retry flags in journal_info

Use the lowest two bits in current->journal_info to encode when
we're holding a glock, and when an operation holding a glock
needs to be retried.

Signed-off-by: Andreas Gruenbacher <agruenba@...hat.com>
---
 fs/gfs2/incore.h | 35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index aa8d1a23132d..e32433df119c 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -871,14 +871,45 @@ static inline unsigned gfs2_max_stuffed_size(const struct gfs2_inode *ip)
 	return GFS2_SB(&ip->i_inode)->sd_sb.sb_bsize - sizeof(struct gfs2_dinode);
 }
 
+/*
+ * Transactions are always memory aligned, so we use bit 0 of
+ * current->journal_info to indicate when we're holding a glock and so taking
+ * random additional glocks might deadlock, and bit 1 to indicate when such an
+ * operation needs to be retried after dropping and re-acquiring that "outer"
+ * glock.
+ */
+
 static inline struct gfs2_trans *current_trans(void)
 {
-	return current->journal_info;
+	return (void *)((long)current->journal_info & ~3);
 }
 
 static inline void set_current_trans(struct gfs2_trans *tr)
 {
-	current->journal_info = tr;
+	long flags = (long)current->journal_info & 3;
+	current->journal_info = (void *)((long)tr | flags);
+}
+
+static inline bool current_holds_glock(void)
+{
+	return (long)current->journal_info & 1;
+}
+
+static inline bool current_needs_retry(void)
+{
+	return (long)current->journal_info & 2;
+}
+
+static inline void set_current_holds_glock(bool b)
+{
+	current->journal_info =
+		(void *)(((long)current->journal_info & ~1) | b);
+}
+
+static inline void set_current_needs_retry(bool b)
+{
+	current->journal_info =
+		(void *)(((long)current->journal_info & ~2) | (b << 1));
 }
 
 #endif /* __INCORE_DOT_H__ */
-- 
2.26.3