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Message-ID: <20130215185644.GB29539@phenom.dumpdata.com>
Date: Fri, 15 Feb 2013 13:56:44 -0500
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Roger Pau Monne <roger.pau@...rix.com>
Cc: linux-kernel@...r.kernel.org, xen-devel@...ts.xen.org
Subject: Re: [PATCH] xen-blkfront: switch from llist to list
> Should be backported to 3.8 stable.
Lets do one thing at a time.
The patch I have in the tree (and that I've asked Jens to pull for 3.9 - so
he might have already in his tree) is the old hybrid where we still use llist
but change the loop from 'for' to 'while'.
This is the stable/for-jens-3.8 tree in git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git
Could you rebase your patch on top of that tree and just simplify the loop?
Sorry about the mess about this - but I had already pulled the trigger
so to say - hoping that Jens would pull the tree and do a git pull to Linus.
And you are absolutly sure that we don't need any extra locking when switching
over to list_head? Say if blkif_completion is called while we are
processing in blkif_queue_request and doing ?
>
> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
> [Part of the description]
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: xen-devel@...ts.xen.org
> ---
> drivers/block/xen-blkfront.c | 27 ++++++++++++++-------------
> include/linux/llist.h | 25 -------------------------
> 2 files changed, 14 insertions(+), 38 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 11043c1..01b91a5 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -44,7 +44,7 @@
> #include <linux/mutex.h>
> #include <linux/scatterlist.h>
> #include <linux/bitmap.h>
> -#include <linux/llist.h>
> +#include <linux/list.h>
>
> #include <xen/xen.h>
> #include <xen/xenbus.h>
> @@ -68,7 +68,7 @@ enum blkif_state {
> struct grant {
> grant_ref_t gref;
> unsigned long pfn;
> - struct llist_node node;
> + struct list_head node;
> };
>
> struct blk_shadow {
> @@ -105,7 +105,7 @@ struct blkfront_info
> struct work_struct work;
> struct gnttab_free_callback callback;
> struct blk_shadow shadow[BLK_RING_SIZE];
> - struct llist_head persistent_gnts;
> + struct list_head persistent_gnts;
> unsigned int persistent_gnts_c;
> unsigned long shadow_free;
> unsigned int feature_flush;
> @@ -371,10 +371,11 @@ static int blkif_queue_request(struct request *req)
> lsect = fsect + (sg->length >> 9) - 1;
>
> if (info->persistent_gnts_c) {
> - BUG_ON(llist_empty(&info->persistent_gnts));
> - gnt_list_entry = llist_entry(
> - llist_del_first(&info->persistent_gnts),
> - struct grant, node);
> + BUG_ON(list_empty(&info->persistent_gnts));
> + gnt_list_entry = list_first_entry(
> + &info->persistent_gnts,
> + struct grant, node);
> + list_del(&gnt_list_entry->node);
>
> ref = gnt_list_entry->gref;
> buffer_mfn = pfn_to_mfn(gnt_list_entry->pfn);
> @@ -790,9 +791,8 @@ static void blkif_restart_queue(struct work_struct *work)
>
> static void blkif_free(struct blkfront_info *info, int suspend)
> {
> - struct llist_node *all_gnts;
> struct grant *persistent_gnt;
> - struct llist_node *n;
> + struct grant *n;
>
> /* Prevent new requests being issued until we fix things up. */
> spin_lock_irq(&info->io_lock);
> @@ -804,8 +804,9 @@ static void blkif_free(struct blkfront_info *info, int suspend)
>
> /* Remove all persistent grants */
> if (info->persistent_gnts_c) {
> - all_gnts = llist_del_all(&info->persistent_gnts);
> - llist_for_each_entry_safe(persistent_gnt, n, all_gnts, node) {
> + list_for_each_entry_safe(persistent_gnt, n,
> + &info->persistent_gnts, node) {
> + list_del(&persistent_gnt->node);
> gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
> __free_page(pfn_to_page(persistent_gnt->pfn));
> kfree(persistent_gnt);
> @@ -868,7 +869,7 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
> }
> /* Add the persistent grant into the list of free grants */
> for (i = 0; i < s->req.u.rw.nr_segments; i++) {
> - llist_add(&s->grants_used[i]->node, &info->persistent_gnts);
> + list_add(&s->grants_used[i]->node, &info->persistent_gnts);
> info->persistent_gnts_c++;
> }
> }
> @@ -1164,7 +1165,7 @@ static int blkfront_probe(struct xenbus_device *dev,
> spin_lock_init(&info->io_lock);
> info->xbdev = dev;
> info->vdevice = vdevice;
> - init_llist_head(&info->persistent_gnts);
> + INIT_LIST_HEAD(&info->persistent_gnts);
> info->persistent_gnts_c = 0;
> info->connected = BLKIF_STATE_DISCONNECTED;
> INIT_WORK(&info->work, blkif_restart_queue);
> diff --git a/include/linux/llist.h b/include/linux/llist.h
> index d0ab98f..a5199f6 100644
> --- a/include/linux/llist.h
> +++ b/include/linux/llist.h
> @@ -125,31 +125,6 @@ static inline void init_llist_head(struct llist_head *list)
> (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
>
> /**
> - * llist_for_each_entry_safe - iterate safely against remove over some entries
> - * of lock-less list of given type.
> - * @pos: the type * to use as a loop cursor.
> - * @n: another type * to use as a temporary storage.
> - * @node: the fist entry of deleted list entries.
> - * @member: the name of the llist_node with the struct.
> - *
> - * In general, some entries of the lock-less list can be traversed
> - * safely only after being removed from list, so start with an entry
> - * instead of list head. This variant allows removal of entries
> - * as we iterate.
> - *
> - * If being used on entries deleted from lock-less list directly, the
> - * traverse order is from the newest to the oldest added entry. If
> - * you want to traverse from the oldest to the newest, you must
> - * reverse the order by yourself before traversing.
> - */
> -#define llist_for_each_entry_safe(pos, n, node, member) \
> - for ((pos) = llist_entry((node), typeof(*(pos)), member), \
> - (n) = (pos)->member.next; \
> - &(pos)->member != NULL; \
> - (pos) = llist_entry(n, typeof(*(pos)), member), \
> - (n) = (&(pos)->member != NULL) ? (pos)->member.next : NULL)
> -
> -/**
> * llist_empty - tests whether a lock-less list is empty
> * @head: the list to test
> *
> --
> 1.7.7.5 (Apple Git-26)
>
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