On Mon, Jan 09, 2017 at 11:56:07AM -0800, Mike Kravetz wrote:
> The routine return_unused_surplus_pages decrements the global
> reservation count, and frees any unused surplus pages that were
> backing the reservation. Commit 7848a4bf51b3 ("mm/hugetlb.c:
> add cond_resched_lock() in return_unused_surplus_pages()") added
> a call to cond_resched_lock in the loop freeing the pages. As
> a result, the hugetlb_lock could be dropped, and someone else
> could use the pages that will be freed in subsequent iterations
> of the loop. This could result in inconsistent global hugetlb
> page state, application api failures (such as mmap) failures or
> application crashes.
>
> When dropping the lock in return_unused_surplus_pages, make sure
> that the global reservation count (resv_huge_pages) remains
> sufficiently large to prevent someone else from claiming pages
> about to be freed.
>
> Fixes: 7848a4bf51b3 ("mm/hugetlb.c: add cond_resched_lock() in
> return_unused_surplus_pages()")
> Reported-and-analyzed-by: Paul Cassella <[email protected]>
> Suggested-by: Michal Hocko <[email protected]>
> Signed-off-by: Mike Kravetz <[email protected]>
> ---
> mm/hugetlb.c | 37 ++++++++++++++++++++++++++++---------
> 1 file changed, 28 insertions(+), 9 deletions(-)
<formletter>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read Documentation/stable_kernel_rules.txt
for how to do this properly.
</formletter>
