xen-blkfront: pre-allocate pages for requests

This prevents us from having to call alloc_page while we are preparing
the request. Since blkfront was calling alloc_page with a spinlock
held we used GFP_ATOMIC, which can fail if we are requesting a lot of
pages since it is using the emergency memory pools.

Allocating all the pages at init prevents us from having to call
alloc_page, thus preventing possible failures.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: xen-devel@lists.xen.org
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 79 insertions, 41 deletions

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 97324cd18f4b..c64043323399 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -165,6 +165,69 @@ static int add_id_to_freelist(struct blkfront_info *info,
         return 0;
 }
 
+static int fill_grant_buffer(struct blkfront_info *info, int num)
+{
+        struct page *granted_page;
+        struct grant *gnt_list_entry, *n;
+        int i = 0;
+
+        while(i < num) {
+                gnt_list_entry = kzalloc(sizeof(struct grant), GFP_NOIO);
+                if (!gnt_list_entry)
+                        goto out_of_memory;
+
+                granted_page = alloc_page(GFP_NOIO);
+                if (!granted_page) {
+                        kfree(gnt_list_entry);
+                        goto out_of_memory;
+                }
+
+                gnt_list_entry->pfn = page_to_pfn(granted_page);
+                gnt_list_entry->gref = GRANT_INVALID_REF;
+                list_add(&gnt_list_entry->node, &info->persistent_gnts);
+                i++;
+        }
+
+        return 0;
+
+out_of_memory:
+        list_for_each_entry_safe(gnt_list_entry, n,
+                                 &info->persistent_gnts, node) {
+                list_del(&gnt_list_entry->node);
+                __free_page(pfn_to_page(gnt_list_entry->pfn));
+                kfree(gnt_list_entry);
+                i--;
+        }
+        BUG_ON(i != 0);
+        return -ENOMEM;
+}
+
+static struct grant *get_grant(grant_ref_t *gref_head,
+                               struct blkfront_info *info)
+{
+        struct grant *gnt_list_entry;
+        unsigned long buffer_mfn;
+
+        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);
+
+        if (gnt_list_entry->gref != GRANT_INVALID_REF) {
+                info->persistent_gnts_c--;
+                return gnt_list_entry;
+        }
+
+        /* Assign a gref to this page */
+        gnt_list_entry->gref = gnttab_claim_grant_reference(gref_head);
+        BUG_ON(gnt_list_entry->gref == -ENOSPC);
+        buffer_mfn = pfn_to_mfn(gnt_list_entry->pfn);
+        gnttab_grant_foreign_access_ref(gnt_list_entry->gref,
+                                        info->xbdev->otherend_id,
+                                        buffer_mfn, 0);
+        return gnt_list_entry;
+}
+
 static const char *op_name(int op)
 {
         static const char *const names[] = {
@@ -306,7 +369,6 @@ static int blkif_queue_request(struct request *req)
          */
         bool new_persistent_gnts;
         grant_ref_t gref_head;
-        struct page *granted_page;
         struct grant *gnt_list_entry = NULL;
         struct scatterlist *sg;
 
@@ -370,42 +432,9 @@ static int blkif_queue_request(struct request *req)
                         fsect = sg->offset >> 9;
                         lsect = fsect + (sg->length >> 9) - 1;
 
-                        if (info->persistent_gnts_c) {
-                                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);
-                                info->persistent_gnts_c--;
-                        } else {
-                                ref = gnttab_claim_grant_reference(&gref_head);
-                                BUG_ON(ref == -ENOSPC);
-
-                                gnt_list_entry =
-                                        kmalloc(sizeof(struct grant),
-                                                         GFP_ATOMIC);
-                                if (!gnt_list_entry)
-                                        return -ENOMEM;
-
-                                granted_page = alloc_page(GFP_ATOMIC);
-                                if (!granted_page) {
-                                        kfree(gnt_list_entry);
-                                        return -ENOMEM;
-                                }
-
-                                gnt_list_entry->pfn =
-                                        page_to_pfn(granted_page);
-                                gnt_list_entry->gref = ref;
-
-                                buffer_mfn = pfn_to_mfn(page_to_pfn(
-                                                                granted_page));
-                                gnttab_grant_foreign_access_ref(ref,
-                                        info->xbdev->otherend_id,
-                                        buffer_mfn, 0);
-                        }
+                        gnt_list_entry = get_grant(&gref_head, info);
+                        ref = gnt_list_entry->gref;
+                        buffer_mfn = pfn_to_mfn(gnt_list_entry->pfn);
 
                         info->shadow[id].grants_used[i] = gnt_list_entry;
 
@@ -803,17 +832,20 @@ static void blkif_free(struct blkfront_info *info, int suspend)
                 blk_stop_queue(info->rq);
 
         /* Remove all persistent grants */
-        if (info->persistent_gnts_c) {
+        if (!list_empty(&info->persistent_gnts)) {
                 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);
+                        if (persistent_gnt->gref != GRANT_INVALID_REF) {
+                                gnttab_end_foreign_access(persistent_gnt->gref,
+                                                          0, 0UL);
+                                info->persistent_gnts_c--;
+                        }
                         __free_page(pfn_to_page(persistent_gnt->pfn));
                         kfree(persistent_gnt);
-                        info->persistent_gnts_c--;
                 }
-                BUG_ON(info->persistent_gnts_c != 0);
         }
+        BUG_ON(info->persistent_gnts_c != 0);
 
         /* No more gnttab callback work. */
         gnttab_cancel_free_callback(&info->callback);
@@ -1008,6 +1040,12 @@ static int setup_blkring(struct xenbus_device *dev,
 
         sg_init_table(info->sg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
 
+        /* Allocate memory for grants */
+        err = fill_grant_buffer(info, BLK_RING_SIZE *
+                                      BLKIF_MAX_SEGMENTS_PER_REQUEST);
+        if (err)
+                goto fail;
+
         err = xenbus_grant_ring(dev, virt_to_mfn(info->ring.sring));
         if (err < 0) {
                 free_page((unsigned long)sring);