Hello Roger Pau Monne,
The patch 0a8704a51f38: "xen/blkback: Persistent grant maps for xen
blk drivers" from Oct 24, 2012, leads to the following warning:
drivers/block/xen-blkfront.c:807 blkif_free()
warn: 'persistent_gnt' was already freed.
807 llist_for_each_entry(persistent_gnt, all_gnts, node) {
808 gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
809 __free_page(pfn_to_page(persistent_gnt->pfn));
810 kfree(persistent_gnt);
^^^^^^^^^^^^^^
We dereference this to find the next element in the list. It will work
if you don't have poisoning enabled or if the memory is not used
immediately by another process. In other words, there will be rare
bugs where this causes a hard to debug crash or if you have poisoning
enabled it will have an easy to debug crash.
811 }
regards,
dan carpenter
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