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SubjectRe: [PATCH] s390/mm: return -ENOMEM in arch_get_unmapped_area[_topdown]
On Thu, 26 Oct 2017 15:36:10 +0800
Li Wang <liwang@redhat.com> wrote:

> That would be very hard to get -ENOMEM returned in crst_table_upgrade()
> because the condition(addr + len <= TASK_SIZE) makes all 'end' value
> is smaller/equal than 'TASK_SIZE_TASK'. So let's move it to the upper
> layer.

I have a hard time understanding what scenario you describe. There is no
'TASK_SIZE_TASK', only TASK_SIZE, TASK_SIZE_OF and TASK_SIZE_MAX.

The code in mmap.c checks for the per-task limit, 31-bit vs 64-bit.
pgalloc.c checks for the maximum allowed address and does not care
about the task.

> Fixes: 8ab867cb0806 (s390/mm: fix BUG_ON in crst_table_upgrade)
> Signed-off-by: Li Wang <liwang@redhat.com>

I don't think this patch fixes anything.

> ---
> arch/s390/mm/mmap.c | 6 ++++++
> arch/s390/mm/pgalloc.c | 3 +--
> 2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
> index 5bea139..8ddb13a 100644
> --- a/arch/s390/mm/mmap.c
> +++ b/arch/s390/mm/mmap.c
> @@ -119,6 +119,9 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
> return addr;
>
> check_asce_limit:
> + if (addr + len >= TASK_SIZE_MAX)
> + return -ENOMEM;
> +
> if (addr + len > current->mm->context.asce_limit &&
> addr + len <= TASK_SIZE) {
> rc = crst_table_upgrade(mm, addr + len);
> @@ -184,6 +187,9 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
> }
>
> check_asce_limit:
> + if (addr + len >= TASK_SIZE_MAX)
> + return -ENOMEM;
> +
> if (addr + len > current->mm->context.asce_limit &&
> addr + len <= TASK_SIZE) {
> rc = crst_table_upgrade(mm, addr + len);
> diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
> index 05f1f27..5e4b887 100644
> --- a/arch/s390/mm/pgalloc.c
> +++ b/arch/s390/mm/pgalloc.c
> @@ -84,8 +84,7 @@ int crst_table_upgrade(struct mm_struct *mm, unsigned long end)
>
> /* upgrade should only happen from 3 to 4, 3 to 5, or 4 to 5 levels */
> VM_BUG_ON(mm->context.asce_limit < _REGION2_SIZE);
> - if (end >= TASK_SIZE_MAX)
> - return -ENOMEM;
> +
> rc = 0;
> notify = 0;
> while (mm->context.asce_limit < end) {


--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.

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