diff options
Diffstat (limited to 'debian/patches-rt/fscache-Use-only-one-fscache_object_cong_wait.patch')
| -rw-r--r-- | debian/patches-rt/fscache-Use-only-one-fscache_object_cong_wait.patch | 123 |
1 files changed, 123 insertions, 0 deletions
diff --git a/debian/patches-rt/fscache-Use-only-one-fscache_object_cong_wait.patch b/debian/patches-rt/fscache-Use-only-one-fscache_object_cong_wait.patch new file mode 100644 index 000000000..4f47d8535 --- /dev/null +++ b/debian/patches-rt/fscache-Use-only-one-fscache_object_cong_wait.patch @@ -0,0 +1,123 @@ +From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Date: Thu, 28 Oct 2021 17:30:50 +0200 +Subject: [PATCH] fscache: Use only one fscache_object_cong_wait. +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.15/older/patches-5.15.3-rt21.tar.xz + +In the commit mentioned below, fscache was converted from slow-work to +workqueue. slow_work_enqueue() and slow_work_sleep_till_thread_needed() +did not use a per-CPU workqueue. They choose from two global waitqueues +depending on the SLOW_WORK_VERY_SLOW bit which was not set so it always +one waitqueue. + +I can't find out how it is ensured that a waiter on certain CPU is woken +up be the other side. My guess is that the timeout in schedule_timeout() +ensures that it does not wait forever (or a random wake up). + +fscache_object_sleep_till_congested() must be invoked from preemptible +context in order for schedule() to work. In this case this_cpu_ptr() +should complain with CONFIG_DEBUG_PREEMPT enabled except the thread is +bound to one CPU. + +wake_up() wakes only one waiter and I'm not sure if it is guaranteed +that only one waiter exists. + +Replace the per-CPU waitqueue with one global waitqueue. + +Fixes: 8b8edefa2fffb ("fscache: convert object to use workqueue instead of slow-work") +Reported-by: Gregor Beck <gregor.beck@gmail.com> +Cc: stable-rt@vger.kernel.org +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Link: https://lkml.kernel.org/r/20211029083839.xwwt7jgzru3kcpii@linutronix.de +--- + fs/fscache/internal.h | 1 - + fs/fscache/main.c | 6 ------ + fs/fscache/object.c | 13 +++++-------- + 3 files changed, 5 insertions(+), 15 deletions(-) + +--- a/fs/fscache/internal.h ++++ b/fs/fscache/internal.h +@@ -81,7 +81,6 @@ extern unsigned fscache_debug; + extern struct kobject *fscache_root; + extern struct workqueue_struct *fscache_object_wq; + extern struct workqueue_struct *fscache_op_wq; +-DECLARE_PER_CPU(wait_queue_head_t, fscache_object_cong_wait); + + extern unsigned int fscache_hash(unsigned int salt, unsigned int *data, unsigned int n); + +--- a/fs/fscache/main.c ++++ b/fs/fscache/main.c +@@ -41,8 +41,6 @@ struct kobject *fscache_root; + struct workqueue_struct *fscache_object_wq; + struct workqueue_struct *fscache_op_wq; + +-DEFINE_PER_CPU(wait_queue_head_t, fscache_object_cong_wait); +- + /* these values serve as lower bounds, will be adjusted in fscache_init() */ + static unsigned fscache_object_max_active = 4; + static unsigned fscache_op_max_active = 2; +@@ -138,7 +136,6 @@ unsigned int fscache_hash(unsigned int s + static int __init fscache_init(void) + { + unsigned int nr_cpus = num_possible_cpus(); +- unsigned int cpu; + int ret; + + fscache_object_max_active = +@@ -161,9 +158,6 @@ static int __init fscache_init(void) + if (!fscache_op_wq) + goto error_op_wq; + +- for_each_possible_cpu(cpu) +- init_waitqueue_head(&per_cpu(fscache_object_cong_wait, cpu)); +- + ret = fscache_proc_init(); + if (ret < 0) + goto error_proc; +--- a/fs/fscache/object.c ++++ b/fs/fscache/object.c +@@ -798,6 +798,8 @@ void fscache_object_destroy(struct fscac + } + EXPORT_SYMBOL(fscache_object_destroy); + ++static DECLARE_WAIT_QUEUE_HEAD(fscache_object_cong_wait); ++ + /* + * enqueue an object for metadata-type processing + */ +@@ -806,16 +808,12 @@ void fscache_enqueue_object(struct fscac + _enter("{OBJ%x}", object->debug_id); + + if (fscache_get_object(object, fscache_obj_get_queue) >= 0) { +- wait_queue_head_t *cong_wq = +- &get_cpu_var(fscache_object_cong_wait); + + if (queue_work(fscache_object_wq, &object->work)) { + if (fscache_object_congested()) +- wake_up(cong_wq); ++ wake_up(&fscache_object_cong_wait); + } else + fscache_put_object(object, fscache_obj_put_queue); +- +- put_cpu_var(fscache_object_cong_wait); + } + } + +@@ -833,16 +831,15 @@ void fscache_enqueue_object(struct fscac + */ + bool fscache_object_sleep_till_congested(signed long *timeoutp) + { +- wait_queue_head_t *cong_wq = this_cpu_ptr(&fscache_object_cong_wait); + DEFINE_WAIT(wait); + + if (fscache_object_congested()) + return true; + +- add_wait_queue_exclusive(cong_wq, &wait); ++ add_wait_queue_exclusive(&fscache_object_cong_wait, &wait); + if (!fscache_object_congested()) + *timeoutp = schedule_timeout(*timeoutp); +- finish_wait(cong_wq, &wait); ++ finish_wait(&fscache_object_cong_wait, &wait); + + return fscache_object_congested(); + } |