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locking/ww_mutex/test: Fix potential workqueue corruption 

[ Upstream commit bccdd80890 ]

In some cases running with the test-ww_mutex code, I was seeing
odd behavior where sometimes it seemed flush_workqueue was
returning before all the work threads were finished.

Often this would cause strange crashes as the mutexes would be
freed while they were being used.

Looking at the code, there is a lifetime problem as the
controlling thread that spawns the work allocates the
"struct stress" structures that are passed to the workqueue
threads. Then when the workqueue threads are finished,
they free the stress struct that was passed to them.

Unfortunately the workqueue work_struct node is in the stress
struct. Which means the work_struct is freed before the work
thread returns and while flush_workqueue is waiting.

It seems like a better idea to have the controlling thread
both allocate and free the stress structures, so that we can
be sure we don't corrupt the workqueue by freeing the structure
prematurely.

So this patch reworks the test to do so, and with this change
I no longer see the early flush_workqueue returns.

Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230922043616.19282-3-jstultz@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
John Stultz 2023-09-22 04:36:00 +00:00 committed by Greg Kroah-Hartman
parent 69e434a1cb
commit c56df79d68
1 changed files with 12 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
kernel/locking/test-ww_mutex.c
View File

@ -466,7 +466,6 @@ retry:
} while (!time_after(jiffies, stress->timeout)); } while (!time_after(jiffies, stress->timeout));
kfree(order); kfree(order);
kfree(stress);
} }
struct reorder_lock { struct reorder_lock {
@ -531,7 +530,6 @@ out:
list_for_each_entry_safe(ll, ln, &locks, link) list_for_each_entry_safe(ll, ln, &locks, link)
kfree(ll); kfree(ll);
kfree(order); kfree(order);
kfree(stress);
} }
static void stress_one_work(struct work_struct *work) static void stress_one_work(struct work_struct *work)
@ -552,8 +550,6 @@ static void stress_one_work(struct work_struct *work)
break; break;
} }
} while (!time_after(jiffies, stress->timeout)); } while (!time_after(jiffies, stress->timeout));
kfree(stress);
} }
#define STRESS_INORDER BIT(0) #define STRESS_INORDER BIT(0)
@ -564,15 +560,24 @@ static void stress_one_work(struct work_struct *work)
static int stress(int nlocks, int nthreads, unsigned int flags) static int stress(int nlocks, int nthreads, unsigned int flags)
{ {
struct ww_mutex *locks; struct ww_mutex *locks;
int n; struct stress *stress_array;
int n, count;
locks = kmalloc_array(nlocks, sizeof(*locks), GFP_KERNEL); locks = kmalloc_array(nlocks, sizeof(*locks), GFP_KERNEL);
if (!locks) if (!locks)
return -ENOMEM; return -ENOMEM;
stress_array = kmalloc_array(nthreads, sizeof(*stress_array),
GFP_KERNEL);
if (!stress_array) {
kfree(locks);
return -ENOMEM;
}
for (n = 0; n < nlocks; n++) for (n = 0; n < nlocks; n++)
ww_mutex_init(&locks[n], &ww_class); ww_mutex_init(&locks[n], &ww_class);
count = 0;
for (n = 0; nthreads; n++) { for (n = 0; nthreads; n++) {
struct stress *stress; struct stress *stress;
void (*fn)(struct work_struct *work); void (*fn)(struct work_struct *work);
@ -596,9 +601,7 @@ static int stress(int nlocks, int nthreads, unsigned int flags)
if (!fn) if (!fn)
continue; continue;
stress = kmalloc(sizeof(*stress), GFP_KERNEL); stress = &stress_array[count++];
if (!stress)
break;
INIT_WORK(&stress->work, fn); INIT_WORK(&stress->work, fn);
stress->locks = locks; stress->locks = locks;
@ -613,6 +616,7 @@ static int stress(int nlocks, int nthreads, unsigned int flags)
for (n = 0; n < nlocks; n++) for (n = 0; n < nlocks; n++)
ww_mutex_destroy(&locks[n]); ww_mutex_destroy(&locks[n]);
kfree(stress_array);
kfree(locks); kfree(locks);
return 0; return 0;