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block: fix elvpriv allocation failure handling

Request allocation is mempool backed to guarantee forward progress
under memory pressure; unfortunately, this property got broken while
adding elvpriv data.  Failures during elvpriv allocation, including
ioc and icq creation failures, currently make get_request() fail as
whole.  There's no forward progress guarantee for these allocations -
they may fail indefinitely under memory pressure stalling IO and
deadlocking the system.

This patch updates get_request() such that elvpriv allocation failure
doesn't make the whole function fail.  If elvpriv allocation fails,
the allocation is degraded into !ELVPRIV.  This will force the request
to ELEVATOR_INSERT_BACK disturbing scheduling but elvpriv alloc
failures should be rare (nothing is per-request) and anything is
better than deadlocking.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
master
Tejun Heo 10 years ago
committed by Jens Axboe
parent
commit
aaf7c68068
  1. 53
      block/blk-core.c

53
block/blk-core.c

@ -29,6 +29,7 @@
#include <linux/fault-inject.h>
#include <linux/list_sort.h>
#include <linux/delay.h>
#include <linux/ratelimit.h>
#define CREATE_TRACE_POINTS
#include <trace/events/block.h>
@ -930,17 +931,6 @@ retry:
rw_flags |= REQ_IO_STAT;
spin_unlock_irq(q->queue_lock);
/* create icq if missing */
if ((rw_flags & REQ_ELVPRIV) && unlikely(et->icq_cache && !icq)) {
create_io_context(gfp_mask, q->node);
ioc = rq_ioc(bio);
if (!ioc)
goto fail_alloc;
icq = ioc_create_icq(ioc, q, gfp_mask);
if (!icq)
goto fail_alloc;
}
/* allocate and init request */
rq = mempool_alloc(q->rq.rq_pool, gfp_mask);
if (!rq)
@ -949,17 +939,28 @@ retry:
blk_rq_init(q, rq);
rq->cmd_flags = rw_flags | REQ_ALLOCED;
/* init elvpriv */
if (rw_flags & REQ_ELVPRIV) {
rq->elv.icq = icq;
if (unlikely(elv_set_request(q, rq, bio, gfp_mask))) {
mempool_free(rq, q->rq.rq_pool);
goto fail_alloc;
if (unlikely(et->icq_cache && !icq)) {
create_io_context(gfp_mask, q->node);
ioc = rq_ioc(bio);
if (!ioc)
goto fail_elvpriv;
icq = ioc_create_icq(ioc, q, gfp_mask);
if (!icq)
goto fail_elvpriv;
}
/* @rq->elv.icq holds on to io_context until @rq is freed */
rq->elv.icq = icq;
if (unlikely(elv_set_request(q, rq, bio, gfp_mask)))
goto fail_elvpriv;
/* @rq->elv.icq holds io_context until @rq is freed */
if (icq)
get_io_context(icq->ioc);
}
out:
/*
* ioc may be NULL here, and ioc_batching will be false. That's
* OK, if the queue is under the request limit then requests need
@ -972,6 +973,24 @@ retry:
trace_block_getrq(q, bio, rw_flags & 1);
return rq;
fail_elvpriv:
/*
* elvpriv init failed. ioc, icq and elvpriv aren't mempool backed
* and may fail indefinitely under memory pressure and thus
* shouldn't stall IO. Treat this request as !elvpriv. This will
* disturb iosched and blkcg but weird is bettern than dead.
*/
printk_ratelimited(KERN_WARNING "%s: request aux data allocation failed, iosched may be disturbed\n",
dev_name(q->backing_dev_info.dev));
rq->cmd_flags &= ~REQ_ELVPRIV;
rq->elv.icq = NULL;
spin_lock_irq(q->queue_lock);
rl->elvpriv--;
spin_unlock_irq(q->queue_lock);
goto out;
fail_alloc:
/*
* Allocation failed presumably due to memory. Undo anything we

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