fs: dlm: change dflags to use atomic bits

Currently manipulating lkb_dflags assumes to held the rsb lock assigned
to the lkb. This is held by dlm message processing after certain
time to lookup the right rsb from the received lkb message id. For user
space locks flags, which is currently the only use case for lkb_dflags,
flags are also being set during dlm character device handling without
holding the rsb lock. To minimize the risk that bit operations are
getting corrupted we switch to atomic bit operations. This patch will
also introduce helpers to snapshot atomic bit values in an non atomic
way. There might be still issues with the flag handling e.g. running in
case of manipulating bit ops and snapshot them at the same time, but this
patch minimize them and will start to use atomic bit operations.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>

1 files changed, 43 insertions, 3 deletions

diff --git a/fs/dlm/dlm_internal.h b/fs/dlm/dlm_internal.h
index 748bb483da1c2..cd4f89217ee19 100644
--- a/fs/dlm/dlm_internal.h
+++ b/fs/dlm/dlm_internal.h
@@ -208,8 +208,10 @@ struct dlm_args {
 
 /* lkb_dflags */
 
-#define DLM_DFL_USER		0x00000001
-#define DLM_DFL_ORPHAN		0x00000002
+#define DLM_DFL_USER_BIT	0
+#define __DLM_DFL_MIN_BIT	DLM_DFL_USER_BIT
+#define DLM_DFL_ORPHAN_BIT	1
+#define __DLM_DFL_MAX_BIT	DLM_DFL_ORPHAN_BIT
 
 #define DLM_CB_CAST		0x00000001
 #define DLM_CB_BAST		0x00000002
@@ -234,7 +236,7 @@ struct dlm_lkb {
 	uint32_t		lkb_exflags;	/* external flags from caller */
 	uint32_t		lkb_sbflags;	/* lksb flags */
 	uint32_t		lkb_flags;	/* internal flags */
-	uint32_t		lkb_dflags;	/* distributed flags */
+	unsigned long		lkb_dflags;	/* distributed flags */
 	unsigned long		lkb_iflags;	/* internal flags */
 	uint32_t		lkb_lvbseq;	/* lvb sequence number */
 
@@ -733,6 +735,44 @@ static inline int dlm_no_directory(struct dlm_ls *ls)
 	return test_bit(LSFL_NODIR, &ls->ls_flags);
 }
 
+/* takes a snapshot from dlm atomic flags */
+static inline uint32_t dlm_flags_val(const unsigned long *addr,
+				     uint32_t min, uint32_t max)
+{
+	uint32_t bit = min, val = 0;
+
+	for_each_set_bit_from(bit, addr, max + 1) {
+		val |= BIT(bit);
+	}
+
+	return val;
+}
+
+static inline uint32_t dlm_dflags_val(const struct dlm_lkb *lkb)
+{
+	return dlm_flags_val(&lkb->lkb_dflags, __DLM_DFL_MIN_BIT,
+			     __DLM_DFL_MAX_BIT);
+}
+
+static inline void dlm_set_flags_val(unsigned long *addr, uint32_t val,
+				     uint32_t min, uint32_t max)
+{
+	uint32_t bit;
+
+	for (bit = min; bit < (max + 1); bit++) {
+		if (val & BIT(bit))
+			set_bit(bit, addr);
+		else
+			clear_bit(bit, addr);
+	}
+}
+
+static inline void dlm_set_dflags_val(struct dlm_lkb *lkb, uint32_t val)
+{
+	dlm_set_flags_val(&lkb->lkb_dflags, val, __DLM_DFL_MIN_BIT,
+			  __DLM_DFL_MAX_BIT);
+}
+
 int dlm_plock_init(void);
 void dlm_plock_exit(void);