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Re: [Xen-devel] [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@xxxxxxxxxx>
> [Part of the description]
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxx
> ---
>  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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