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authorJeff Moyer <jmoyer@redhat.com>2015-01-12 15:21:01 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-03-06 14:40:50 -0800
commit8a9a6a13371bac27f6cd7c9fc52f9b1ee98c2ba4 (patch)
tree50345dca5362df2efe8b63a487aced5f2c21c334 /block
parenta8ace7cca0c77f9140a25ed175e4d0aaa5d77566 (diff)
downloadlinux-linaro-stable-8a9a6a13371bac27f6cd7c9fc52f9b1ee98c2ba4.tar.gz
cfq-iosched: fix incorrect filing of rt async cfqq
commit c6ce194325cef342313e3d27620411ce90a89c50 upstream. Hi, If you can manage to submit an async write as the first async I/O from the context of a process with realtime scheduling priority, then a cfq_queue is allocated, but filed into the wrong async_cfqq bucket. It ends up in the best effort array, but actually has realtime I/O scheduling priority set in cfqq->ioprio. The reason is that cfq_get_queue assumes the default scheduling class and priority when there is no information present (i.e. when the async cfqq is created): static struct cfq_queue * cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic, struct bio *bio, gfp_t gfp_mask) { const int ioprio_class = IOPRIO_PRIO_CLASS(cic->ioprio); const int ioprio = IOPRIO_PRIO_DATA(cic->ioprio); cic->ioprio starts out as 0, which is "invalid". So, class of 0 (IOPRIO_CLASS_NONE) is passed to cfq_async_queue_prio like so: async_cfqq = cfq_async_queue_prio(cfqd, ioprio_class, ioprio); static struct cfq_queue ** cfq_async_queue_prio(struct cfq_data *cfqd, int ioprio_class, int ioprio) { switch (ioprio_class) { case IOPRIO_CLASS_RT: return &cfqd->async_cfqq[0][ioprio]; case IOPRIO_CLASS_NONE: ioprio = IOPRIO_NORM; /* fall through */ case IOPRIO_CLASS_BE: return &cfqd->async_cfqq[1][ioprio]; case IOPRIO_CLASS_IDLE: return &cfqd->async_idle_cfqq; default: BUG(); } } Here, instead of returning a class mapped from the process' scheduling priority, we get back the bucket associated with IOPRIO_CLASS_BE. Now, there is no queue allocated there yet, so we create it: cfqq = cfq_find_alloc_queue(cfqd, is_sync, cic, bio, gfp_mask); That function ends up doing this: cfq_init_cfqq(cfqd, cfqq, current->pid, is_sync); cfq_init_prio_data(cfqq, cic); cfq_init_cfqq marks the priority as having changed. Then, cfq_init_prio data does this: ioprio_class = IOPRIO_PRIO_CLASS(cic->ioprio); switch (ioprio_class) { default: printk(KERN_ERR "cfq: bad prio %x\n", ioprio_class); case IOPRIO_CLASS_NONE: /* * no prio set, inherit CPU scheduling settings */ cfqq->ioprio = task_nice_ioprio(tsk); cfqq->ioprio_class = task_nice_ioclass(tsk); break; So we basically have two code paths that treat IOPRIO_CLASS_NONE differently, which results in an RT async cfqq filed into a best effort bucket. Attached is a patch which fixes the problem. I'm not sure how to make it cleaner. Suggestions would be welcome. Signed-off-by: Jeff Moyer <jmoyer@redhat.com> Tested-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com> Signed-off-by: Jens Axboe <axboe@fb.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'block')
-rw-r--r--block/cfq-iosched.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 537244c2c7ef..69111c5c352c 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3646,12 +3646,17 @@ static struct cfq_queue *
cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
struct bio *bio, gfp_t gfp_mask)
{
- const int ioprio_class = IOPRIO_PRIO_CLASS(cic->ioprio);
- const int ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
+ int ioprio_class = IOPRIO_PRIO_CLASS(cic->ioprio);
+ int ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
struct cfq_queue **async_cfqq = NULL;
struct cfq_queue *cfqq = NULL;
if (!is_sync) {
+ if (!ioprio_valid(cic->ioprio)) {
+ struct task_struct *tsk = current;
+ ioprio = task_nice_ioprio(tsk);
+ ioprio_class = task_nice_ioclass(tsk);
+ }
async_cfqq = cfq_async_queue_prio(cfqd, ioprio_class, ioprio);
cfqq = *async_cfqq;
}