[Xen-devel] [PATCH] xen/privcmd: sprinkle around cond_resched() calls in mmap ioctl handling

["Jan Beulich" <JBeulich@xxxxxxxx>]

Many of these operations can take arbitrarily long, which can become a
problem irrespective of them being exposed to privileged users only.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 drivers/xen/privcmd.c |   18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

--- 4.7-rc6-xen.orig/drivers/xen/privcmd.c
+++ 4.7-rc6-xen/drivers/xen/privcmd.c
@@ -69,9 +69,13 @@ static long privcmd_ioctl_hypercall(void
 static void free_page_list(struct list_head *pages)
 {
        struct page *p, *n;
+       unsigned idx = 0;
 
-       list_for_each_entry_safe(p, n, pages, lru)
+       list_for_each_entry_safe(p, n, pages, lru) {
+               if (!(++idx & 7))
+                       cond_resched();
                __free_page(p);
+       }
 
        INIT_LIST_HEAD(pages);
 }
@@ -103,6 +107,8 @@ static int gather_array(struct list_head
                        if (page == NULL)
                                goto fail;
 
+                       if (pagedata)
+                               cond_resched();
                        pagedata = page_address(page);
 
                        list_add_tail(&page->lru, pagelist);
@@ -144,6 +150,9 @@ static int traverse_pages(unsigned nelem
        while (nelem--) {
                if (pageidx > PAGE_SIZE-size) {
                        struct page *page;
+
+                       if (pagedata)
+                               cond_resched();
                        pos = pos->next;
                        page = list_entry(pos, struct page, lru);
                        pagedata = page_address(page);
@@ -169,16 +178,17 @@ static int traverse_pages_block(unsigned
                                void *state)
 {
        void *pagedata;
-       unsigned pageidx;
+       unsigned pageidx = 0;
        int ret = 0;
 
        BUG_ON(size > PAGE_SIZE);
 
-       pageidx = PAGE_SIZE;
-
        while (nelem) {
                int nr = (PAGE_SIZE/size);
                struct page *page;
+
+               if (pageidx++)
+                       cond_resched();
                if (nr > nelem)
                        nr = nelem;
                pos = pos->next;




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