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mm/damon: simplify stop mechanism
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A kernel thread can exit gracefully with kthread_stop().  So we don't
need a new flag 'kdamond_stop'.  And to make sure the task struct is not
freed when accessing it, get reference to it before termination.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Changbin Du <[email protected]>
Reviewed-by: SeongJae Park <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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changbindu authored and torvalds committed Nov 6, 2021
1 parent 0d16cfd commit 0f91d13
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Showing 2 changed files with 15 additions and 37 deletions.
1 change: 0 additions & 1 deletion include/linux/damon.h
Original file line number Diff line number Diff line change
Expand Up @@ -381,7 +381,6 @@ struct damon_ctx {

/* public: */
struct task_struct *kdamond;
bool kdamond_stop;
struct mutex kdamond_lock;

struct damon_primitive primitive;
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51 changes: 15 additions & 36 deletions mm/damon/core.c
Original file line number Diff line number Diff line change
Expand Up @@ -390,17 +390,6 @@ static unsigned long damon_region_sz_limit(struct damon_ctx *ctx)
return sz;
}

static bool damon_kdamond_running(struct damon_ctx *ctx)
{
bool running;

mutex_lock(&ctx->kdamond_lock);
running = ctx->kdamond != NULL;
mutex_unlock(&ctx->kdamond_lock);

return running;
}

static int kdamond_fn(void *data);

/*
Expand All @@ -418,7 +407,6 @@ static int __damon_start(struct damon_ctx *ctx)
mutex_lock(&ctx->kdamond_lock);
if (!ctx->kdamond) {
err = 0;
ctx->kdamond_stop = false;
ctx->kdamond = kthread_run(kdamond_fn, ctx, "kdamond.%d",
nr_running_ctxs);
if (IS_ERR(ctx->kdamond)) {
Expand Down Expand Up @@ -474,13 +462,15 @@ int damon_start(struct damon_ctx **ctxs, int nr_ctxs)
*/
static int __damon_stop(struct damon_ctx *ctx)
{
struct task_struct *tsk;

mutex_lock(&ctx->kdamond_lock);
if (ctx->kdamond) {
ctx->kdamond_stop = true;
tsk = ctx->kdamond;
if (tsk) {
get_task_struct(tsk);
mutex_unlock(&ctx->kdamond_lock);
while (damon_kdamond_running(ctx))
usleep_range(ctx->sample_interval,
ctx->sample_interval * 2);
kthread_stop(tsk);
put_task_struct(tsk);
return 0;
}
mutex_unlock(&ctx->kdamond_lock);
Expand Down Expand Up @@ -925,12 +915,8 @@ static bool kdamond_need_update_primitive(struct damon_ctx *ctx)
static bool kdamond_need_stop(struct damon_ctx *ctx)
{
struct damon_target *t;
bool stop;

mutex_lock(&ctx->kdamond_lock);
stop = ctx->kdamond_stop;
mutex_unlock(&ctx->kdamond_lock);
if (stop)
if (kthread_should_stop())
return true;

if (!ctx->primitive.target_valid)
Expand Down Expand Up @@ -1021,13 +1007,6 @@ static int kdamond_wait_activation(struct damon_ctx *ctx)
return -EBUSY;
}

static void set_kdamond_stop(struct damon_ctx *ctx)
{
mutex_lock(&ctx->kdamond_lock);
ctx->kdamond_stop = true;
mutex_unlock(&ctx->kdamond_lock);
}

/*
* The monitoring daemon that runs as a kernel thread
*/
Expand All @@ -1038,25 +1017,26 @@ static int kdamond_fn(void *data)
struct damon_region *r, *next;
unsigned int max_nr_accesses = 0;
unsigned long sz_limit = 0;
bool done = false;

pr_debug("kdamond (%d) starts\n", current->pid);

if (ctx->primitive.init)
ctx->primitive.init(ctx);
if (ctx->callback.before_start && ctx->callback.before_start(ctx))
set_kdamond_stop(ctx);
done = true;

sz_limit = damon_region_sz_limit(ctx);

while (!kdamond_need_stop(ctx)) {
while (!kdamond_need_stop(ctx) && !done) {
if (kdamond_wait_activation(ctx))
continue;

if (ctx->primitive.prepare_access_checks)
ctx->primitive.prepare_access_checks(ctx);
if (ctx->callback.after_sampling &&
ctx->callback.after_sampling(ctx))
set_kdamond_stop(ctx);
done = true;

usleep_range(ctx->sample_interval, ctx->sample_interval + 1);

Expand All @@ -1069,7 +1049,7 @@ static int kdamond_fn(void *data)
sz_limit);
if (ctx->callback.after_aggregation &&
ctx->callback.after_aggregation(ctx))
set_kdamond_stop(ctx);
done = true;
kdamond_apply_schemes(ctx);
kdamond_reset_aggregated(ctx);
kdamond_split_regions(ctx);
Expand All @@ -1088,9 +1068,8 @@ static int kdamond_fn(void *data)
damon_destroy_region(r, t);
}

if (ctx->callback.before_terminate &&
ctx->callback.before_terminate(ctx))
set_kdamond_stop(ctx);
if (ctx->callback.before_terminate)
ctx->callback.before_terminate(ctx);
if (ctx->primitive.cleanup)
ctx->primitive.cleanup(ctx);

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