Let's cc Uladzislau on vmalloc things?
How about this?
Well, lol, that's a simple approach to avoiding the problem ;)
To me it looks like a specific workaround for a specific one user.
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();} @@ -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.
Maybe solve it on zsmalloc side? For example to add __zs_unmap_object_deferred(), so it schedules the work that calls unmap_kernel_range() on a list of mapping_area objects.
-- Vlad Rezki