[PATCH 02/13] gfs2: Retries missing in gfs2_{rename,exchange}

[Andreas Gruenbacher <agruenba@redhat.com>]

Fix a bug in gfs2's asynchronous glock handling for rename and exchange
operations.  The original async implementation from commit ad26967b9afa
("gfs2: Use async glocks for rename") mentioned that retries were needed
but never implemented them, causing operations to fail with -ESTALE
instead of retrying on timeout.

Also makes the waiting interruptible.

In addition, the timeouts used were too high for situations in which
timing out is a rare but expected scenario.  Switch to shorter timeouts
with randomization and exponentional backoff.

Fixes: ad26967b9afa ("gfs2: Use async glocks for rename")
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
 fs/gfs2/glock.c | 36 +++++++++++++++++++++++++++---------
 fs/gfs2/glock.h |  3 ++-
 fs/gfs2/inode.c | 18 ++++++++++++++----
 3 files changed, 43 insertions(+), 14 deletions(-)

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 47e8809575d5..f358448d7b3d 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1284,31 +1284,45 @@ static int glocks_pending(unsigned int num_gh, struct gfs2_holder *ghs)
  * gfs2_glock_async_wait - wait on multiple asynchronous glock acquisitions
  * @num_gh: the number of holders in the array
  * @ghs: the glock holder array
+ * @retries: number of retries attempted so far
  *
  * Returns: 0 on success, meaning all glocks have been granted and are held.
  *          -ESTALE if the request timed out, meaning all glocks were released,
  *          and the caller should retry the operation.
  */
 
-int gfs2_glock_async_wait(unsigned int num_gh, struct gfs2_holder *ghs)
+int gfs2_glock_async_wait(unsigned int num_gh, struct gfs2_holder *ghs,
+			  unsigned int retries)
 {
 	struct gfs2_sbd *sdp = ghs[0].gh_gl->gl_name.ln_sbd;
-	int i, ret = 0, timeout = 0;
 	unsigned long start_time = jiffies;
+	int i, ret = 0;
+	long timeout;
 
 	might_sleep();
-	/*
-	 * Total up the (minimum hold time * 2) of all glocks and use that to
-	 * determine the max amount of time we should wait.
-	 */
-	for (i = 0; i < num_gh; i++)
-		timeout += ghs[i].gh_gl->gl_hold_time << 1;
 
-	if (!wait_event_timeout(sdp->sd_async_glock_wait,
+	timeout = GL_GLOCK_MIN_HOLD;
+	if (retries) {
+		unsigned int max_shift;
+		long incr;
+
+		/* Add a random delay and increase the timeout exponentially. */
+		max_shift = BITS_PER_LONG - 2 - __fls(GL_GLOCK_HOLD_INCR);
+		incr = min(GL_GLOCK_HOLD_INCR << min(retries - 1, max_shift),
+			   10 * HZ - GL_GLOCK_MIN_HOLD);
+		schedule_timeout_interruptible(get_random_long() % (incr / 3));
+		if (signal_pending(current))
+			goto interrupted;
+		timeout += (incr / 3) + get_random_long() % (incr / 3);
+	}
+
+	if (!wait_event_interruptible_timeout(sdp->sd_async_glock_wait,
 				!glocks_pending(num_gh, ghs), timeout)) {
 		ret = -ESTALE; /* request timed out. */
 		goto out;
 	}
+	if (signal_pending(current))
+		goto interrupted;
 
 	for (i = 0; i < num_gh; i++) {
 		struct gfs2_holder *gh = &ghs[i];
@@ -1332,6 +1346,10 @@ int gfs2_glock_async_wait(unsigned int num_gh, struct gfs2_holder *ghs)
 		}
 	}
 	return ret;
+
+interrupted:
+	ret = -EINTR;
+	goto out;
 }
 
 /**
diff --git a/fs/gfs2/glock.h b/fs/gfs2/glock.h
index 55d5985f32a0..dccbf36b8cb1 100644
--- a/fs/gfs2/glock.h
+++ b/fs/gfs2/glock.h
@@ -204,7 +204,8 @@ int gfs2_glock_poll(struct gfs2_holder *gh);
 int gfs2_instantiate(struct gfs2_holder *gh);
 int gfs2_glock_holder_ready(struct gfs2_holder *gh);
 int gfs2_glock_wait(struct gfs2_holder *gh);
-int gfs2_glock_async_wait(unsigned int num_gh, struct gfs2_holder *ghs);
+int gfs2_glock_async_wait(unsigned int num_gh, struct gfs2_holder *ghs,
+			  unsigned int retries);
 void gfs2_glock_dq(struct gfs2_holder *gh);
 void gfs2_glock_dq_wait(struct gfs2_holder *gh);
 void gfs2_glock_dq_uninit(struct gfs2_holder *gh);
diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c
index 36618e353199..b6ed069b3487 100644
--- a/fs/gfs2/inode.c
+++ b/fs/gfs2/inode.c
@@ -1495,7 +1495,7 @@ static int gfs2_rename(struct inode *odir, struct dentry *odentry,
 	unsigned int num_gh;
 	int dir_rename = 0;
 	struct gfs2_diradd da = { .nr_blocks = 0, .save_loc = 0, };
-	unsigned int x;
+	unsigned int retries = 0, x;
 	int error;
 
 	gfs2_holder_mark_uninitialized(&r_gh);
@@ -1545,12 +1545,17 @@ static int gfs2_rename(struct inode *odir, struct dentry *odentry,
 		num_gh++;
 	}
 
+again:
 	for (x = 0; x < num_gh; x++) {
 		error = gfs2_glock_nq(ghs + x);
 		if (error)
 			goto out_gunlock;
 	}
-	error = gfs2_glock_async_wait(num_gh, ghs);
+	error = gfs2_glock_async_wait(num_gh, ghs, retries);
+	if (error == -ESTALE) {
+		retries++;
+		goto again;
+	}
 	if (error)
 		goto out_gunlock;
 
@@ -1739,7 +1744,7 @@ static int gfs2_exchange(struct inode *odir, struct dentry *odentry,
 	struct gfs2_sbd *sdp = GFS2_SB(odir);
 	struct gfs2_holder ghs[4], r_gh;
 	unsigned int num_gh;
-	unsigned int x;
+	unsigned int retries = 0, x;
 	umode_t old_mode = oip->i_inode.i_mode;
 	umode_t new_mode = nip->i_inode.i_mode;
 	int error;
@@ -1783,13 +1788,18 @@ static int gfs2_exchange(struct inode *odir, struct dentry *odentry,
 	gfs2_holder_init(nip->i_gl, LM_ST_EXCLUSIVE, GL_ASYNC, ghs + num_gh);
 	num_gh++;
 
+again:
 	for (x = 0; x < num_gh; x++) {
 		error = gfs2_glock_nq(ghs + x);
 		if (error)
 			goto out_gunlock;
 	}
 
-	error = gfs2_glock_async_wait(num_gh, ghs);
+	error = gfs2_glock_async_wait(num_gh, ghs, retries);
+	if (error == -ESTALE) {
+		retries++;
+		goto again;
+	}
 	if (error)
 		goto out_gunlock;
 
-- 
2.52.0