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SubjectRe: [PATCH 2/3] uprobes: change build_map_info() to try kmalloc(GFP_NOWAIT) first
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On Mon, 2012-06-04 at 16:53 +0200, Oleg Nesterov wrote:
> build_map_info() doesn't allocate the memory under i_mmap_mutex
> to avoid the deadlock with page reclaim. But it can try GFP_NOWAIT
> first, it should work in the likely case and thus we almost never
> need the pre-alloc-and-retry path.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
> kernel/events/uprobes.c | 9 +++++++--
> 1 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index a1bbcab..c9836ae 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -772,8 +772,13 @@ build_map_info(struct address_space *mapping, loff_t offset, bool is_register)
> continue;
>
> if (!prev) {
> - more++;
> - continue;


Should we add something like this:

/*
* Needs GFP_NOWAIT to avoid i_mmap_mutex recursion through reclaim.
* This is optimistic, no harm done if it fails.
*/

> + prev = kmalloc(sizeof(struct map_info),
> + GFP_NOWAIT | __GFP_NOMEMALLOC | __GFP_NOWARN);
> + if (!prev) {
> + more++;
> + continue;
> + }
> + prev->next = NULL;
> }
>
> if (!atomic_inc_not_zero(&vma->vm_mm->mm_users))



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