From: Eric Paris Date: Tue, 22 Nov 2005 05:32:28 +0000 (-0800) Subject: [PATCH] hugetlb: fix race in set_max_huge_pages for multiple updaters of nr_huge_pages X-Git-Tag: v2.6.15-rc3~104 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0bd0f9fb190a0fc0fb25b764c8b04869711f7657;p=pandora-kernel.git [PATCH] hugetlb: fix race in set_max_huge_pages for multiple updaters of nr_huge_pages If there are multiple updaters to /proc/sys/vm/nr_hugepages simultaneously it is possible for the nr_huge_pages variable to become incorrect. There is no locking in the set_max_huge_pages function around alloc_fresh_huge_page which is able to update nr_huge_pages. Two callers to alloc_fresh_huge_page could race against each other as could a call to alloc_fresh_huge_page and a call to update_and_free_page. This patch just expands the area covered by the hugetlb_lock to cover the call into alloc_fresh_huge_page. I'm not sure how we could say that a sysctl section is performance critical where more specific locking would be needed. My reproducer was to run a couple copies of the following script simultaneously while [ true ]; do echo 1000 > /proc/sys/vm/nr_hugepages echo 500 > /proc/sys/vm/nr_hugepages echo 750 > /proc/sys/vm/nr_hugepages echo 100 > /proc/sys/vm/nr_hugepages echo 0 > /proc/sys/vm/nr_hugepages done and then watch /proc/meminfo and eventually you will see things like HugePages_Total: 100 HugePages_Free: 109 After applying the patch all seemed well. Signed-off-by: Eric Paris Acked-by: William Irwin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed