Let's cc Uladzislau on vmalloc things?
> How about this?
Well, lol, that's a simple approach to avoiding the problem ;)
> unmap_kernel_range had been atomic operation and zsmalloc has used
> it in atomic context in zs_unmap_object.
> However, ("e47110e90584, mm/vunmap: add cond_resched() in vunmap_pmd_range")
> changed it into non-atomic operation via adding cond_resched.
> It causes zram decompresion failure by corrupting compressed buffer
> in atomic context.
>
> This patch introduces unmap_kernel_range_atomic which works for
> only range less than PMD_SIZE to prevent cond_resched call.
>
> ...
>
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -180,6 +180,7 @@ int map_kernel_range(unsigned long start, unsigned long
> size, pgprot_t prot,
> struct page **pages);
> extern void unmap_kernel_range_noflush(unsigned long addr, unsigned long
> size);
> extern void unmap_kernel_range(unsigned long addr, unsigned long size);
> +extern void unmap_kernel_range_atomic(unsigned long addr, unsigned long
> size);
> static inline void set_vm_flush_reset_perms(void *addr)
> {
> struct vm_struct *vm = find_vm_area(addr);
> @@ -200,6 +201,7 @@ unmap_kernel_range_noflush(unsigned long addr, unsigned
> long size)
> {
> }
> #define unmap_kernel_range unmap_kernel_range_noflush
> +#define unmap_kernel_range_atomic unmap_kernel_range_noflush
> static inline void set_vm_flush_reset_perms(void *addr)
> {
> }
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index d7075ad340aa..714e5425dc45 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -88,6 +88,7 @@ static void vunmap_pmd_range(pud_t *pud, unsigned long
> addr, unsigned long end,
> pmd_t *pmd;
> unsigned long next;
> int cleared;
> + bool check_resched = (end - addr) > PMD_SIZE;
>
> pmd = pmd_offset(pud, addr);
> do {
> @@ -102,8 +103,8 @@ static void vunmap_pmd_range(pud_t *pud, unsigned long
> addr, unsigned long end,
> if (pmd_none_or_clear_bad(pmd))
> continue;
> vunmap_pte_range(pmd, addr, next, mask);
> -
> - cond_resched();
> + if (check_resched)
> + cond_resched();
> } while (pmd++, addr = next, addr != end);
> }
>
> @@ -2024,6 +2025,24 @@ void unmap_kernel_range(unsigned long addr, unsigned
> long size)
> flush_tlb_kernel_range(addr, end);
> }
>
> +/**
> + * unmap_kernel_range_atomic - unmap kernel VM area and flush cache and TLB
> + * @addr: start of the VM area to unmap
> + * @size: size of the VM area to unmap
> + *
> + * Similar to unmap_kernel_range_noflush() but it's atomic. @size should be
> + * less than PMD_SIZE.
> + */
> +void unmap_kernel_range_atomic(unsigned long addr, unsigned long size)
> +{
> + unsigned long end = addr + size;
> +
> + flush_cache_vunmap(addr, end);
> + WARN_ON(size > PMD_SIZE);
WARN_ON_ONCE() would be better here - no point in creating a million
warnings where one would suffice.
> + unmap_kernel_range_noflush(addr, size);
> + flush_tlb_kernel_range(addr, end);
> +}
> +
> static inline void setup_vmalloc_vm_locked(struct vm_struct *vm,
> struct vmap_area *va, unsigned long flags, const void *caller)
> {
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 662ee420706f..9decc7634852 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1154,7 +1154,7 @@ static inline void __zs_unmap_object(struct
> mapping_area *area,
> {
> unsigned long addr = (unsigned long)area->vm_addr;
>
> - unmap_kernel_range(addr, PAGE_SIZE * 2);
> + unmap_kernel_range_atomic(addr, PAGE_SIZE * 2);
> }
I suppose we could live with it if no better solutions are forthcoming.
