[PATCH v5] powerpc/pseries/vas: Migration suspend waits for no in-progress open windows
Haren Myneni
haren at linux.ibm.com
Sun Nov 26 10:51:04 AEDT 2023
The hypervisor returns migration failure if all VAS windows are not
closed. During pre-migration stage, vas_migration_handler() sets
migration_in_progress flag and closes all windows from the list.
The allocate VAS window routine checks the migration flag, setup
the window and then add it to the list. So there is possibility of
the migration handler missing the window that is still in the
process of setup.
t1: Allocate and open VAS t2: Migration event
window
lock vas_pseries_mutex
If migration_in_progress set
unlock vas_pseries_mutex
return
open window HCALL
unlock vas_pseries_mutex
Modify window HCALL lock vas_pseries_mutex
setup window migration_in_progress=true
Closes all windows from the list
// May miss windows that are
// not in the list
unlock vas_pseries_mutex
lock vas_pseries_mutex return
if nr_closed_windows == 0
// No DLPAR CPU or migration
add window to the list
// Window will be added to the
// list after the setup is completed
unlock vas_pseries_mutex
return
unlock vas_pseries_mutex
Close VAS window
// due to DLPAR CPU or migration
return -EBUSY
This patch resolves the issue with the following steps:
- Set the migration_in_progress flag without holding mutex.
- Introduce nr_open_wins_progress counter in VAS capabilities
struct
- This counter tracks the number of open windows are still in
progress
- The allocate setup window thread closes windows if the migration
is set and decrements nr_open_window_progress counter
- The migration handler waits for no in-progress open windows.
The code flow with the fix is as follows:
t1: Allocate and open VAS t2: Migration event
window
lock vas_pseries_mutex
If migration_in_progress set
unlock vas_pseries_mutex
return
open window HCALL
nr_open_wins_progress++
// Window opened, but not
// added to the list yet
unlock vas_pseries_mutex
Modify window HCALL migration_in_progress=true
setup window lock vas_pseries_mutex
Closes all windows from the list
While nr_open_wins_progress {
unlock vas_pseries_mutex
lock vas_pseries_mutex sleep
if nr_closed_windows == 0 // Wait if any open window in
or migration is not started // progress. The open window
// No DLPAR CPU or migration // thread closes the window without
add window to the list // adding to the list and return if
nr_open_wins_progress-- // the migration is in progress.
unlock vas_pseries_mutex
return
Close VAS window
nr_open_wins_progress--
unlock vas_pseries_mutex
return -EBUSY lock vas_pseries_mutex
}
unlock vas_pseries_mutex
return
Fixes: 37e6764895ef ("powerpc/pseries/vas: Add VAS migration handler")
Signed-off-by: Haren Myneni <haren at linux.ibm.com>
---
v1 -> v2:
- Do not define the migration_in_progress flag as atomic as
suggested by Nathan
v2 -> v3:
- Use wait_event() instead of wait_event_interruptible() so that
returns after all windows are closed as suggested by Nathan
v3 -> v4:
- remove atomic for nr_open_wins_progress counter as suggested by
Nathan and Michael Ellerman
- Use sleep instead of wait_event_interruptible() to check
nr_open_wins_progress counter under mutex.
v4 -> v5:
- Update the commit message with comments in the code flow and added
the second code flow with the fix as suggested by Michael Ellerman
---
arch/powerpc/platforms/pseries/vas.c | 51 ++++++++++++++++++++++++----
arch/powerpc/platforms/pseries/vas.h | 2 ++
2 files changed, 46 insertions(+), 7 deletions(-)
diff --git a/arch/powerpc/platforms/pseries/vas.c b/arch/powerpc/platforms/pseries/vas.c
index b1f25bac280b..71d52a670d95 100644
--- a/arch/powerpc/platforms/pseries/vas.c
+++ b/arch/powerpc/platforms/pseries/vas.c
@@ -385,11 +385,15 @@ static struct vas_window *vas_allocate_window(int vas_id, u64 flags,
* same fault IRQ is not freed by the OS before.
*/
mutex_lock(&vas_pseries_mutex);
- if (migration_in_progress)
+ if (migration_in_progress) {
rc = -EBUSY;
- else
+ } else {
rc = allocate_setup_window(txwin, (u64 *)&domain[0],
cop_feat_caps->win_type);
+ if (!rc)
+ caps->nr_open_wins_progress++;
+ }
+
mutex_unlock(&vas_pseries_mutex);
if (rc)
goto out;
@@ -404,8 +408,17 @@ static struct vas_window *vas_allocate_window(int vas_id, u64 flags,
goto out_free;
txwin->win_type = cop_feat_caps->win_type;
- mutex_lock(&vas_pseries_mutex);
+
/*
+ * The migration SUSPEND thread sets migration_in_progress and
+ * closes all open windows from the list. But the window is
+ * added to the list after open and modify HCALLs. So possible
+ * that migration_in_progress is set before modify HCALL which
+ * may cause some windows are still open when the hypervisor
+ * initiates the migration.
+ * So checks the migration_in_progress flag again and close all
+ * open windows.
+ *
* Possible to lose the acquired credit with DLPAR core
* removal after the window is opened. So if there are any
* closed windows (means with lost credits), do not give new
@@ -413,9 +426,11 @@ static struct vas_window *vas_allocate_window(int vas_id, u64 flags,
* after the existing windows are reopened when credits are
* available.
*/
- if (!caps->nr_close_wins) {
+ mutex_lock(&vas_pseries_mutex);
+ if (!caps->nr_close_wins && !migration_in_progress) {
list_add(&txwin->win_list, &caps->list);
caps->nr_open_windows++;
+ caps->nr_open_wins_progress--;
mutex_unlock(&vas_pseries_mutex);
vas_user_win_add_mm_context(&txwin->vas_win.task_ref);
return &txwin->vas_win;
@@ -433,6 +448,12 @@ static struct vas_window *vas_allocate_window(int vas_id, u64 flags,
*/
free_irq_setup(txwin);
h_deallocate_vas_window(txwin->vas_win.winid);
+ /*
+ * Hold mutex and reduce nr_open_wins_progress counter.
+ */
+ mutex_lock(&vas_pseries_mutex);
+ caps->nr_open_wins_progress--;
+ mutex_unlock(&vas_pseries_mutex);
out:
atomic_dec(&cop_feat_caps->nr_used_credits);
kfree(txwin);
@@ -937,14 +958,14 @@ int vas_migration_handler(int action)
struct vas_caps *vcaps;
int i, rc = 0;
+ pr_info("VAS migration event %d\n", action);
+
/*
* NX-GZIP is not enabled. Nothing to do for migration.
*/
if (!copypaste_feat)
return rc;
- mutex_lock(&vas_pseries_mutex);
-
if (action == VAS_SUSPEND)
migration_in_progress = true;
else
@@ -990,12 +1011,27 @@ int vas_migration_handler(int action)
switch (action) {
case VAS_SUSPEND:
+ mutex_lock(&vas_pseries_mutex);
rc = reconfig_close_windows(vcaps, vcaps->nr_open_windows,
true);
+ /*
+ * Windows are included in the list after successful
+ * open. So wait for closing these in-progress open
+ * windows in vas_allocate_window() which will be
+ * done if the migration_in_progress is set.
+ */
+ while (vcaps->nr_open_wins_progress) {
+ mutex_unlock(&vas_pseries_mutex);
+ msleep(10);
+ mutex_lock(&vas_pseries_mutex);
+ }
+ mutex_unlock(&vas_pseries_mutex);
break;
case VAS_RESUME:
+ mutex_lock(&vas_pseries_mutex);
atomic_set(&caps->nr_total_credits, new_nr_creds);
rc = reconfig_open_windows(vcaps, new_nr_creds, true);
+ mutex_unlock(&vas_pseries_mutex);
break;
default:
/* should not happen */
@@ -1011,8 +1047,9 @@ int vas_migration_handler(int action)
goto out;
}
+ pr_info("VAS migration event (%d) successful\n", action);
+
out:
- mutex_unlock(&vas_pseries_mutex);
return rc;
}
diff --git a/arch/powerpc/platforms/pseries/vas.h b/arch/powerpc/platforms/pseries/vas.h
index 7115043ec488..45567cd13178 100644
--- a/arch/powerpc/platforms/pseries/vas.h
+++ b/arch/powerpc/platforms/pseries/vas.h
@@ -91,6 +91,8 @@ struct vas_cop_feat_caps {
struct vas_caps {
struct vas_cop_feat_caps caps;
struct list_head list; /* List of open windows */
+ int nr_open_wins_progress; /* Number of open windows in */
+ /* progress. Used in migration */
int nr_close_wins; /* closed windows in the hypervisor for DLPAR */
int nr_open_windows; /* Number of successful open windows */
u8 feat; /* Feature type */
--
2.26.3
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