[Cluster-devel] [GFS2 PATCH v3] gfs2: Use async glocks for rename
Bob Peterson
rpeterso at redhat.com
Thu Aug 29 17:27:10 UTC 2019
Hi,
Here is version 3 of this patch. It's the same as version 2, except
I'm now using gfs2_glock_dq rather than gfs2_glock_dq_wait.
---
Because s_vfs_rename_mutex is not cluster-wide, multiple nodes can
reverse the roles of which directories are "old" and which are "new"
for the purposes of rename. This can cause AB-BA deadlocks where two
nodes can lock old-then-new but since their roles are reversed, they
wait for each other.
There can be several layers of directory dependencies across many
nodes.
This patch fixes the problem by acquiring all gfs2_rename's inode
glocks asychronously and waits for all glocks to be acquired.
That way all inodes are locked regardless of the order.
The timeout value for multiple asynchronous glocks is calculated to
be the total of the individual wait times for each glock times two.
Since gfs2_exchange is very similar to gfs2_rename, both functions
are patched in the same way.
A new async glock wait queue, sd_async_glock_wait, keeps a list of
waiters for these events. If gfs2's holder_wake function detects an
async holder, it wakes up any waiters for the event. The waiter
only tests whether any of its requests are still pending.
Since the glocks are sent to dlm asychronously, the wait function
needs to check to see which glocks, if any, were granted.
If a glock is granted by dlm (and therefore held) its minimum hold
time is checked and adjusted as necessary, as other glock grants do.
If the event times out, all glocks held thus far must be dequeued.
Then, if there are any glocks unaccounted for (IOW, glocks stuck in
AB-BA deadlocks) should eventually be granted when the other node
is finished doing its conflicting rename. We need to loop around
and wait for dlm to respond to those lock requests too.
Releasing the held locks frees the other node from its deadlock.
After we release all requests, we return -ESTALE to the caller
(vfs rename) which loops around and retries the request.
Node1 Node2
--------- ---------
1. Enqueue A Enqueue B
2. Enqueue B Enqueue A
3. A granted
6. B granted
7. Wait for B
8. Wait for A
9. A times out (since Node 1 holds A)
10. Dequeue B (since it was granted)
11. Wait for all requests from DLM
12. B Granted (since Node2 released it in step 10)
13. Rename
14. Dequeue A
15. DLM Grants A
16. Dequeue A (due to the timeout and since we
no longer have B held for our task).
17. Dequeue B
18. Return -ESTALE to vfs
19. VFS retries the operation, goto step 1.
This release-all-locks / acquire-all-locks may slow it down as both
nodes struggle in the same way and do the same thing. However, it
should only slow down rename and exchange, and only in cases where
there is contention for the same inodes, which ought to be rare.
Signed-off-by: Bob Peterson <rpeterso at redhat.com>
---
fs/gfs2/glock.c | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++-
fs/gfs2/glock.h | 6 +++
fs/gfs2/incore.h | 1 +
fs/gfs2/inode.c | 34 +++++++++++------
fs/gfs2/ops_fstype.c | 1 +
5 files changed, 132 insertions(+), 13 deletions(-)
diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index a27dbd3dec01..46c243e63954 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -305,6 +305,11 @@ static void gfs2_holder_wake(struct gfs2_holder *gh)
clear_bit(HIF_WAIT, &gh->gh_iflags);
smp_mb__after_atomic();
wake_up_bit(&gh->gh_iflags, HIF_WAIT);
+ if (gh->gh_flags & GL_ASYNC) {
+ struct gfs2_sbd *sdp = gh->gh_gl->gl_name.ln_sbd;
+
+ wake_up(&sdp->sd_async_glock_wait);
+ }
}
/**
@@ -952,6 +957,100 @@ int gfs2_glock_wait(struct gfs2_holder *gh)
return gh->gh_error;
}
+static int glocks_pending(unsigned int num_gh, struct gfs2_holder *ghs)
+{
+ int i;
+
+ for (i = 0; i < num_gh; i++)
+ if (test_bit(HIF_WAIT, &ghs[i].gh_iflags))
+ return 1;
+ return 0;
+}
+
+/**
+ * gfs2_glock_async_wait - wait on multiple asynchronous glock acquisitions
+ * @num_gh: the number of holders in the array
+ * @ghs: the glock holder array
+ *
+ * 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)
+{
+ struct gfs2_sbd *sdp = ghs[0].gh_gl->gl_name.ln_sbd;
+ int i, ret = 0, requests = num_gh, timeout = 0;
+ unsigned long t1 = jiffies;
+
+ 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);
+
+wait_for_dlm:
+ if (!wait_event_timeout(sdp->sd_async_glock_wait,
+ !glocks_pending(num_gh, ghs), timeout))
+ ret = -ESTALE; /* request timed out. */
+
+ /**
+ * Now we need to run through all the holders.
+ * If our request timed out, we need to repeatedly release any held
+ * glocks we acquired thus far to prevent AB-BA deadlocks. Later, they
+ * must be reacquired by the caller.
+ *
+ * If dlm sent us any errors, we need to run the list and return the
+ * first error we find. We use the HIF_WAIT bit to tell requests that
+ * still need a response from dlm.
+ *
+ * If dlm granted all our requests, we need to adjust the glock
+ * minimum hold time values according to how long we waited.
+ *
+ * Dlm may send us callbacks granting any non-held locks at any
+ * time, so we must take care not to race with them. If we loop around
+ * before we fully acquire them, dlm can grant the lock and cause us
+ * to try to re-acquire a lock that's already been granted.
+ *
+ * To avoid this, we must repeatedly wait for dlm to reply to them all,
+ * one by one, then release the held glocks until all our requests
+ * have been dequeued. When all are dequeued in this manner, we can
+ * return the error and, if -ESTALE, the request can be retried.
+ */
+ for (i = 0; i < num_gh; i++) {
+ if (!gfs2_holder_queued(&ghs[i])) /* not queued to a glock */
+ continue;
+ if (test_bit(HIF_WAIT, &ghs[i].gh_iflags)) /* Still pending? */
+ continue;
+
+ BUG_ON(!requests);
+ requests--;
+ if (test_bit(HIF_HOLDER, &ghs[i].gh_iflags)) {
+ if (ret == -ESTALE) /* Timed out a different holder's
+ request, so unlock this one. */
+ gfs2_glock_dq(&ghs[i]);
+ else if (time_after(jiffies, t1 + HZ))
+ /* Lengthen the minimum hold time. */
+ ghs[i].gh_gl->gl_hold_time =
+ min(ghs[i].gh_gl->gl_hold_time +
+ GL_GLOCK_HOLD_INCR,
+ GL_GLOCK_MAX_HOLD);
+ }
+ if (!ret && ghs[i].gh_error)
+ ret = ghs[i].gh_error;
+ }
+
+ if (requests) /* still pending requests to dlm? */
+ goto wait_for_dlm;
+
+ /**
+ * At this point, we've either acquired all locks or released them all.
+ **/
+ return ret;
+}
+
/**
* handle_callback - process a demote request
* @gl: the glock
@@ -1018,9 +1117,9 @@ __acquires(&gl->gl_lockref.lock)
struct gfs2_holder *gh2;
int try_futile = 0;
- BUG_ON(gh->gh_owner_pid == NULL);
+ GLOCK_BUG_ON(gl, gh->gh_owner_pid == NULL);
if (test_and_set_bit(HIF_WAIT, &gh->gh_iflags))
- BUG();
+ GLOCK_BUG_ON(gl, true);
if (gh->gh_flags & (LM_FLAG_TRY | LM_FLAG_TRY_1CB)) {
if (test_bit(GLF_LOCK, &gl->gl_flags))
diff --git a/fs/gfs2/glock.h b/fs/gfs2/glock.h
index e4e0bed5257c..b8adaf80e4c5 100644
--- a/fs/gfs2/glock.h
+++ b/fs/gfs2/glock.h
@@ -190,6 +190,7 @@ extern void gfs2_holder_uninit(struct gfs2_holder *gh);
extern int gfs2_glock_nq(struct gfs2_holder *gh);
extern int gfs2_glock_poll(struct gfs2_holder *gh);
extern int gfs2_glock_wait(struct gfs2_holder *gh);
+extern int gfs2_glock_async_wait(unsigned int num_gh, struct gfs2_holder *ghs);
extern void gfs2_glock_dq(struct gfs2_holder *gh);
extern void gfs2_glock_dq_wait(struct gfs2_holder *gh);
extern void gfs2_glock_dq_uninit(struct gfs2_holder *gh);
@@ -260,6 +261,11 @@ static inline bool gfs2_holder_initialized(struct gfs2_holder *gh)
return gh->gh_gl;
}
+static inline bool gfs2_holder_queued(struct gfs2_holder *gh)
+{
+ return !list_empty(&gh->gh_list);
+}
+
/**
* glock_set_object - set the gl_object field of a glock
* @gl: the glock
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 7a993d7c022e..6b450065b9d5 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -725,6 +725,7 @@ struct gfs2_sbd {
struct gfs2_glock *sd_freeze_gl;
struct work_struct sd_freeze_work;
wait_queue_head_t sd_glock_wait;
+ wait_queue_head_t sd_async_glock_wait;
atomic_t sd_glock_disposal;
struct completion sd_locking_init;
struct completion sd_wdack;
diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c
index 50eeb15c6f4f..e1e18fb587eb 100644
--- a/fs/gfs2/inode.c
+++ b/fs/gfs2/inode.c
@@ -1388,16 +1388,18 @@ static int gfs2_rename(struct inode *odir, struct dentry *odentry,
}
num_gh = 1;
- gfs2_holder_init(odip->i_gl, LM_ST_EXCLUSIVE, 0, ghs);
+ gfs2_holder_init(odip->i_gl, LM_ST_EXCLUSIVE, GL_ASYNC, ghs);
if (odip != ndip) {
- gfs2_holder_init(ndip->i_gl, LM_ST_EXCLUSIVE, 0, ghs + num_gh);
+ gfs2_holder_init(ndip->i_gl, LM_ST_EXCLUSIVE,GL_ASYNC,
+ ghs + num_gh);
num_gh++;
}
- gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, ghs + num_gh);
+ gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, GL_ASYNC, ghs + num_gh);
num_gh++;
if (nip) {
- gfs2_holder_init(nip->i_gl, LM_ST_EXCLUSIVE, 0, ghs + num_gh);
+ gfs2_holder_init(nip->i_gl, LM_ST_EXCLUSIVE, GL_ASYNC,
+ ghs + num_gh);
num_gh++;
}
@@ -1406,6 +1408,9 @@ static int gfs2_rename(struct inode *odir, struct dentry *odentry,
if (error)
goto out_gunlock;
}
+ error = gfs2_glock_async_wait(num_gh, ghs);
+ if (error)
+ goto out_gunlock;
if (nip) {
/* Grab the resource group glock for unlink flag twiddling.
@@ -1555,7 +1560,8 @@ static int gfs2_rename(struct inode *odir, struct dentry *odentry,
gfs2_glock_dq_uninit(&rd_gh);
while (x--) {
- gfs2_glock_dq(ghs + x);
+ if (gfs2_holder_queued(ghs + x))
+ gfs2_glock_dq(ghs + x);
gfs2_holder_uninit(ghs + x);
}
out_gunlock_r:
@@ -1585,7 +1591,7 @@ static int gfs2_exchange(struct inode *odir, struct dentry *odentry,
struct gfs2_inode *oip = GFS2_I(odentry->d_inode);
struct gfs2_inode *nip = GFS2_I(ndentry->d_inode);
struct gfs2_sbd *sdp = GFS2_SB(odir);
- struct gfs2_holder ghs[5], r_gh;
+ struct gfs2_holder ghs[4], r_gh;
unsigned int num_gh;
unsigned int x;
umode_t old_mode = oip->i_inode.i_mode;
@@ -1619,15 +1625,16 @@ static int gfs2_exchange(struct inode *odir, struct dentry *odentry,
}
num_gh = 1;
- gfs2_holder_init(odip->i_gl, LM_ST_EXCLUSIVE, 0, ghs);
+ gfs2_holder_init(odip->i_gl, LM_ST_EXCLUSIVE, GL_ASYNC, ghs);
if (odip != ndip) {
- gfs2_holder_init(ndip->i_gl, LM_ST_EXCLUSIVE, 0, ghs + num_gh);
+ gfs2_holder_init(ndip->i_gl, LM_ST_EXCLUSIVE, GL_ASYNC,
+ ghs + num_gh);
num_gh++;
}
- gfs2_holder_init(oip->i_gl, LM_ST_EXCLUSIVE, 0, ghs + num_gh);
+ gfs2_holder_init(oip->i_gl, LM_ST_EXCLUSIVE, GL_ASYNC, ghs + num_gh);
num_gh++;
- gfs2_holder_init(nip->i_gl, LM_ST_EXCLUSIVE, 0, ghs + num_gh);
+ gfs2_holder_init(nip->i_gl, LM_ST_EXCLUSIVE, GL_ASYNC, ghs + num_gh);
num_gh++;
for (x = 0; x < num_gh; x++) {
@@ -1636,6 +1643,10 @@ static int gfs2_exchange(struct inode *odir, struct dentry *odentry,
goto out_gunlock;
}
+ error = gfs2_glock_async_wait(num_gh, ghs);
+ if (error)
+ goto out_gunlock;
+
error = -ENOENT;
if (oip->i_inode.i_nlink == 0 || nip->i_inode.i_nlink == 0)
goto out_gunlock;
@@ -1696,7 +1707,8 @@ static int gfs2_exchange(struct inode *odir, struct dentry *odentry,
gfs2_trans_end(sdp);
out_gunlock:
while (x--) {
- gfs2_glock_dq(ghs + x);
+ if (gfs2_holder_queued(ghs + x))
+ gfs2_glock_dq(ghs + x);
gfs2_holder_uninit(ghs + x);
}
out_gunlock_r:
diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 4a8e5a7310f0..f3fd5cd9d43f 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -87,6 +87,7 @@ static struct gfs2_sbd *init_sbd(struct super_block *sb)
gfs2_tune_init(&sdp->sd_tune);
init_waitqueue_head(&sdp->sd_glock_wait);
+ init_waitqueue_head(&sdp->sd_async_glock_wait);
atomic_set(&sdp->sd_glock_disposal, 0);
init_completion(&sdp->sd_locking_init);
init_completion(&sdp->sd_wdack);
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