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Message-Id: <20220106004656.126790-4-daniel.m.jordan@oracle.com>
Date: Wed, 5 Jan 2022 19:46:43 -0500
From: Daniel Jordan <daniel.m.jordan@...cle.com>
To: Alexander Duyck <alexanderduyck@...com>,
Alex Williamson <alex.williamson@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Ben Segall <bsegall@...gle.com>,
Cornelia Huck <cohuck@...hat.com>,
Dan Williams <dan.j.williams@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Herbert Xu <herbert@...dor.apana.org.au>,
Ingo Molnar <mingo@...hat.com>,
Jason Gunthorpe <jgg@...dia.com>,
Johannes Weiner <hannes@...xchg.org>,
Josh Triplett <josh@...htriplett.org>,
Michal Hocko <mhocko@...e.com>, Nico Pache <npache@...hat.com>,
Pasha Tatashin <pasha.tatashin@...een.com>,
Peter Zijlstra <peterz@...radead.org>,
Steffen Klassert <steffen.klassert@...unet.com>,
Steve Sistare <steven.sistare@...cle.com>,
Tejun Heo <tj@...nel.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Vincent Guittot <vincent.guittot@...aro.org>
Cc: linux-mm@...ck.org, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
Daniel Jordan <daniel.m.jordan@...cle.com>
Subject: [RFC 03/16] padata: Add undo support
Jobs can fail midway through their work. To recover, the finished
chunks of work need to be undone in a job-specific way.
Let padata_do_multithreaded callers specify an "undo" callback
responsible for undoing one chunk of a job. To avoid multiple levels of
error handling, do not allow the callback to fail. Undoing is
singlethreaded to keep it simple and because it's a slow path.
Signed-off-by: Daniel Jordan <daniel.m.jordan@...cle.com>
---
include/linux/padata.h | 6 +++
kernel/padata.c | 113 +++++++++++++++++++++++++++++++++++------
2 files changed, 103 insertions(+), 16 deletions(-)
diff --git a/include/linux/padata.h b/include/linux/padata.h
index 1c8670a24ccf..2a9fa459463d 100644
--- a/include/linux/padata.h
+++ b/include/linux/padata.h
@@ -135,6 +135,10 @@ struct padata_shell {
* @min_chunk: The minimum chunk size in job-specific units. This allows
* the client to communicate the minimum amount of work that's
* appropriate for one worker thread to do at once.
+ * @undo_fn: A function that undoes one chunk of the task per call. If
+ * error(s) occur during the job, this is called on all successfully
+ * completed chunks. The chunk(s) in which failure occurs should be
+ * handled in the thread function.
* @max_threads: Max threads to use for the job, actual number may be less
* depending on task size and minimum chunk size.
*/
@@ -145,6 +149,8 @@ struct padata_mt_job {
unsigned long size;
unsigned long align;
unsigned long min_chunk;
+
+ void (*undo_fn)(unsigned long start, unsigned long end, void *arg);
int max_threads;
};
diff --git a/kernel/padata.c b/kernel/padata.c
index 1596ca22b316..d0876f861464 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -29,6 +29,7 @@
#include <linux/cpumask.h>
#include <linux/err.h>
#include <linux/cpu.h>
+#include <linux/list_sort.h>
#include <linux/padata.h>
#include <linux/mutex.h>
#include <linux/sched.h>
@@ -42,6 +43,10 @@ struct padata_work {
struct work_struct pw_work;
struct list_head pw_list; /* padata_free_works linkage */
void *pw_data;
+ /* holds job units from padata_mt_job::start to pw_error_start */
+ unsigned long pw_error_offset;
+ unsigned long pw_error_start;
+ unsigned long pw_error_end;
};
static DEFINE_SPINLOCK(padata_works_lock);
@@ -56,6 +61,9 @@ struct padata_mt_job_state {
int nworks_fini;
int error; /* first error from thread_fn */
unsigned long chunk_size;
+ unsigned long position;
+ unsigned long remaining_size;
+ struct list_head failed_works;
};
static void padata_free_pd(struct parallel_data *pd);
@@ -447,26 +455,38 @@ static void padata_mt_helper(struct work_struct *w)
spin_lock(&ps->lock);
- while (job->size > 0 && ps->error == 0) {
- unsigned long start, size, end;
+ while (ps->remaining_size > 0 && ps->error == 0) {
+ unsigned long position, position_offset, size, end;
int ret;
- start = job->start;
+ position_offset = job->size - ps->remaining_size;
+ position = ps->position;
/* So end is chunk size aligned if enough work remains. */
- size = roundup(start + 1, ps->chunk_size) - start;
- size = min(size, job->size);
- end = start + size;
+ size = roundup(position + 1, ps->chunk_size) - position;
+ size = min(size, ps->remaining_size);
+ end = position + size;
- job->start = end;
- job->size -= size;
+ ps->position = end;
+ ps->remaining_size -= size;
spin_unlock(&ps->lock);
- ret = job->thread_fn(start, end, job->fn_arg);
+
+ ret = job->thread_fn(position, end, job->fn_arg);
+
spin_lock(&ps->lock);
- /* Save first error code only. */
- if (ps->error == 0)
- ps->error = ret;
+ if (ret) {
+ /* Save first error code only. */
+ if (ps->error == 0)
+ ps->error = ret;
+ /* Save information about where the job failed. */
+ if (job->undo_fn) {
+ list_move(&pw->pw_list, &ps->failed_works);
+ pw->pw_error_start = position;
+ pw->pw_error_offset = position_offset;
+ pw->pw_error_end = end;
+ }
+ }
}
++ps->nworks_fini;
@@ -477,6 +497,60 @@ static void padata_mt_helper(struct work_struct *w)
complete(&ps->completion);
}
+static int padata_error_cmp(void *unused, const struct list_head *a,
+ const struct list_head *b)
+{
+ struct padata_work *work_a = list_entry(a, struct padata_work, pw_list);
+ struct padata_work *work_b = list_entry(b, struct padata_work, pw_list);
+
+ if (work_a->pw_error_offset < work_b->pw_error_offset)
+ return -1;
+ else if (work_a->pw_error_offset > work_b->pw_error_offset)
+ return 1;
+ return 0;
+}
+
+static void padata_undo(struct padata_mt_job_state *ps,
+ struct list_head *works_list,
+ struct padata_work *stack_work)
+{
+ struct list_head *failed_works = &ps->failed_works;
+ struct padata_mt_job *job = ps->job;
+ unsigned long undo_pos = job->start;
+
+ /* Sort so the failed ranges can be checked as we go. */
+ list_sort(NULL, failed_works, padata_error_cmp);
+
+ /* Undo completed work on this node, skipping failed ranges. */
+ while (undo_pos != ps->position) {
+ struct padata_work *failed_work;
+ unsigned long undo_end;
+
+ failed_work = list_first_entry_or_null(failed_works,
+ struct padata_work,
+ pw_list);
+ if (failed_work)
+ undo_end = failed_work->pw_error_start;
+ else
+ undo_end = ps->position;
+
+ if (undo_pos != undo_end)
+ job->undo_fn(undo_pos, undo_end, job->fn_arg);
+
+ if (failed_work) {
+ undo_pos = failed_work->pw_error_end;
+ /* main thread's stack_work stays off works_list */
+ if (failed_work == stack_work)
+ list_del(&failed_work->pw_list);
+ else
+ list_move(&failed_work->pw_list, works_list);
+ } else {
+ undo_pos = undo_end;
+ }
+ }
+ WARN_ON_ONCE(!list_empty(failed_works));
+}
+
/**
* padata_do_multithreaded - run a multithreaded job
* @job: Description of the job.
@@ -509,10 +583,13 @@ int padata_do_multithreaded(struct padata_mt_job *job)
spin_lock_init(&ps.lock);
init_completion(&ps.completion);
- ps.job = job;
- ps.nworks = padata_work_alloc_mt(nworks, &ps, &works);
- ps.nworks_fini = 0;
- ps.error = 0;
+ INIT_LIST_HEAD(&ps.failed_works);
+ ps.job = job;
+ ps.nworks = padata_work_alloc_mt(nworks, &ps, &works);
+ ps.nworks_fini = 0;
+ ps.error = 0;
+ ps.position = job->start;
+ ps.remaining_size = job->size;
/*
* Chunk size is the amount of work a helper does per call to the
@@ -529,11 +606,15 @@ int padata_do_multithreaded(struct padata_mt_job *job)
/* Use the current thread, which saves starting a workqueue worker. */
padata_work_init(&my_work, padata_mt_helper, &ps, PADATA_WORK_ONSTACK);
+ INIT_LIST_HEAD(&my_work.pw_list);
padata_mt_helper(&my_work.pw_work);
/* Wait for all the helpers to finish. */
wait_for_completion(&ps.completion);
+ if (ps.error && job->undo_fn)
+ padata_undo(&ps, &works, &my_work);
+
destroy_work_on_stack(&my_work.pw_work);
padata_works_free(&works);
return ps.error;
--
2.34.1
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