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Date: Mon, 27 Jan 2014 17:19:41 +0100
From: Roger Pau Monné <roger.pau@...rix.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC: <xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
David Vrabel <david.vrabel@...rix.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Matt Rushton <mrushton@...zon.com>,
Matt Wilson <msw@...zon.com>,
Ian Campbell <Ian.Campbell@...rix.com>
Subject: Re: [PATCH] xen-blkback: fix memory leaks
On 27/01/14 17:09, Konrad Rzeszutek Wilk wrote:
> On Mon, Jan 27, 2014 at 11:13:41AM +0100, Roger Pau Monne wrote:
>> I've at least identified two possible memory leaks in blkback, both
>> related to the shutdown path of a VBD:
>>
>> - We don't wait for any pending purge work to finish before cleaning
>> the list of free_pages. The purge work will call put_free_pages and
>> thus we might end up with pages being added to the free_pages list
>> after we have emptied it.
>> - We don't wait for pending requests to end before cleaning persistent
>> grants and the list of free_pages. Again this can add pages to the
>> free_pages lists or persistent grants to the persistent_gnts
>> red-black tree.
>>
>> Also, add some checks in xen_blkif_free to make sure we are cleaning
>> everything.
>>
>> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
>> Cc: David Vrabel <david.vrabel@...rix.com>
>> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>> Cc: Matt Rushton <mrushton@...zon.com>
>> Cc: Matt Wilson <msw@...zon.com>
>> Cc: Ian Campbell <Ian.Campbell@...rix.com>
>> ---
>> This should be applied after the patch:
>>
>> xen-blkback: fix memory leak when persistent grants are used
>
> Could you respin the series with the issues below fixed and
> have said patch as part of the series. That way not only does
> it have your SoB on it but it makes it easier to apply the patch
> for lazy^H^H^Hbusy maintainers and makes it clear that you had
> tested both of them.
>
> Also, please CC Jens Axboe on these patches.
Ack, will do once the comments below are sorted out.
>>
>> >From Matt Rushton & Matt Wilson and backported to stable.
>>
>> I've been able to create and destroy ~4000 guests while doing heavy IO
>> operations with this patch on a 512M Dom0 without problems.
>> ---
>> drivers/block/xen-blkback/blkback.c | 29 +++++++++++++++++++----------
>> drivers/block/xen-blkback/xenbus.c | 9 +++++++++
>> 2 files changed, 28 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
>> index 30ef7b3..19925b7 100644
>> --- a/drivers/block/xen-blkback/blkback.c
>> +++ b/drivers/block/xen-blkback/blkback.c
>> @@ -169,6 +169,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>> struct pending_req *pending_req);
>> static void make_response(struct xen_blkif *blkif, u64 id,
>> unsigned short op, int st);
>> +static void xen_blk_drain_io(struct xen_blkif *blkif, bool force);
>>
>> #define foreach_grant_safe(pos, n, rbtree, node) \
>> for ((pos) = container_of(rb_first((rbtree)), typeof(*(pos)), node), \
>> @@ -625,6 +626,12 @@ purge_gnt_list:
>> print_stats(blkif);
>> }
>>
>> + /* Drain pending IO */
>> + xen_blk_drain_io(blkif, true);
>> +
>> + /* Drain pending purge work */
>> + flush_work(&blkif->persistent_purge_work);
>> +
>> /* Free all persistent grant pages */
>> if (!RB_EMPTY_ROOT(&blkif->persistent_gnts))
>> free_persistent_gnts(blkif, &blkif->persistent_gnts,
>> @@ -930,7 +937,7 @@ static int dispatch_other_io(struct xen_blkif *blkif,
>> return -EIO;
>> }
>>
>> -static void xen_blk_drain_io(struct xen_blkif *blkif)
>> +static void xen_blk_drain_io(struct xen_blkif *blkif, bool force)
>> {
>> atomic_set(&blkif->drain, 1);
>> do {
>> @@ -943,7 +950,7 @@ static void xen_blk_drain_io(struct xen_blkif *blkif)
>>
>> if (!atomic_read(&blkif->drain))
>> break;
>> - } while (!kthread_should_stop());
>> + } while (!kthread_should_stop() || force);
>> atomic_set(&blkif->drain, 0);
>> }
>>
>> @@ -976,17 +983,19 @@ static void __end_block_io_op(struct pending_req *pending_req, int error)
>> * the proper response on the ring.
>> */
>> if (atomic_dec_and_test(&pending_req->pendcnt)) {
>> - xen_blkbk_unmap(pending_req->blkif,
>> + struct xen_blkif *blkif = pending_req->blkif;
>> +
>> + xen_blkbk_unmap(blkif,
>> pending_req->segments,
>> pending_req->nr_pages);
>> - make_response(pending_req->blkif, pending_req->id,
>> + make_response(blkif, pending_req->id,
>> pending_req->operation, pending_req->status);
>> - xen_blkif_put(pending_req->blkif);
>> - if (atomic_read(&pending_req->blkif->refcnt) <= 2) {
>> - if (atomic_read(&pending_req->blkif->drain))
>> - complete(&pending_req->blkif->drain_complete);
>> + free_req(blkif, pending_req);
>> + xen_blkif_put(blkif);
>> + if (atomic_read(&blkif->refcnt) <= 2) {
>> + if (atomic_read(&blkif->drain))
>> + complete(&blkif->drain_complete);
>> }
>> - free_req(pending_req->blkif, pending_req);
>> }
>> }
>>
>> @@ -1224,7 +1233,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>> * issue the WRITE_FLUSH.
>> */
>> if (drain)
>> - xen_blk_drain_io(pending_req->blkif);
>> + xen_blk_drain_io(pending_req->blkif, false);
>>
>> /*
>> * If we have failed at this point, we need to undo the M2P override,
>> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
>> index c2014a0..3c10281 100644
>> --- a/drivers/block/xen-blkback/xenbus.c
>> +++ b/drivers/block/xen-blkback/xenbus.c
>> @@ -125,6 +125,7 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
>> blkif->persistent_gnts.rb_node = NULL;
>> spin_lock_init(&blkif->free_pages_lock);
>> INIT_LIST_HEAD(&blkif->free_pages);
>> + INIT_LIST_HEAD(&blkif->persistent_purge_list);
>
> Hm,
See comment below.
>> blkif->free_pages_num = 0;
>> atomic_set(&blkif->persistent_gnt_in_use, 0);
>>
>> @@ -259,6 +260,14 @@ static void xen_blkif_free(struct xen_blkif *blkif)
>> if (!atomic_dec_and_test(&blkif->refcnt))
>> BUG();
>>
>> + /* Make sure everything is drained before shutting down */
>> + BUG_ON(blkif->persistent_gnt_c != 0);
>> + BUG_ON(atomic_read(&blkif->persistent_gnt_in_use) != 0);
>> + BUG_ON(blkif->free_pages_num != 0);
>> + BUG_ON(!list_empty(&blkif->persistent_purge_list));
>
> You don't seem to put anything on this list? Or even declare this?
> Was there another patch in the series?
No, the list is already used in current code, but it is initialized only
before usage, now I need to make sure it's initialized even if not used, or:
BUG_ON(!list_empty(&blkif->persistent_purge_list));
Is going to fail.
I will resend this and replace the other (now useless) initialization
with a BUG_ON(!list_empty...
>
>> + BUG_ON(!list_empty(&blkif->free_pages));
>> + BUG_ON(!RB_EMPTY_ROOT(&blkif->persistent_gnts));
>> +
>> /* Check that there is no request in use */
>> list_for_each_entry_safe(req, n, &blkif->pending_free, free_list) {
>> list_del(&req->free_list);
>> --
>> 1.7.7.5 (Apple Git-26)
>>
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