mm: VMA sequence count
Wrap the VMA modifications (vma_adjust/unmap_page_range) with sequence
counts such that we can easily test if a VMA is changed.
The unmap_page_range() one allows us to make assumptions about
page-tables; when we find the seqcount hasn't changed we can assume
page-tables are still valid.
The flip side is that we cannot distinguish between a vma_adjust() and
the unmap_page_range() -- where with the former we could have
re-checked the vma bounds against the address.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
[Port to 4.12 kernel]
[Build depends on CONFIG_SPECULATIVE_PAGE_FAULT]
[Introduce vm_write_* inline function depending on
CONFIG_SPECULATIVE_PAGE_FAULT]
[Fix lock dependency between mapping->i_mmap_rwsem and vma->vm_sequence by
using vm_raw_write* functions]
[Fix a lock dependency warning in mmap_region() when entering the error
path]
[move sequence initialisation INIT_VMA()]
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Change-Id: Ibc23ef3b9dbb80323c0f24cb06da34b4c3a8fa71
Patch-mainline: linux-mm @ 17 Apr 2018 16:33:14
[vinmenon@codeaurora.org: trivial merge conflict fixes]
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a34e7f9..c18a355 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1174,6 +1174,9 @@
static inline void INIT_VMA(struct vm_area_struct *vma)
{
INIT_LIST_HEAD(&vma->anon_vma_chain);
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+ seqcount_init(&vma->vm_sequence);
+#endif
}
struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
@@ -1245,6 +1248,47 @@
unmap_mapping_range(mapping, holebegin, holelen, 0);
}
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+static inline void vm_write_begin(struct vm_area_struct *vma)
+{
+ write_seqcount_begin(&vma->vm_sequence);
+}
+static inline void vm_write_begin_nested(struct vm_area_struct *vma,
+ int subclass)
+{
+ write_seqcount_begin_nested(&vma->vm_sequence, subclass);
+}
+static inline void vm_write_end(struct vm_area_struct *vma)
+{
+ write_seqcount_end(&vma->vm_sequence);
+}
+static inline void vm_raw_write_begin(struct vm_area_struct *vma)
+{
+ raw_write_seqcount_begin(&vma->vm_sequence);
+}
+static inline void vm_raw_write_end(struct vm_area_struct *vma)
+{
+ raw_write_seqcount_end(&vma->vm_sequence);
+}
+#else
+static inline void vm_write_begin(struct vm_area_struct *vma)
+{
+}
+static inline void vm_write_begin_nested(struct vm_area_struct *vma,
+ int subclass)
+{
+}
+static inline void vm_write_end(struct vm_area_struct *vma)
+{
+}
+static inline void vm_raw_write_begin(struct vm_area_struct *vma)
+{
+}
+static inline void vm_raw_write_end(struct vm_area_struct *vma)
+{
+}
+#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */
+
extern void truncate_pagecache(struct inode *inode, loff_t new);
extern void truncate_setsize(struct inode *inode, loff_t newsize);
void pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to);
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 5942478..0568861 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -365,6 +365,9 @@
struct mempolicy *vm_policy; /* NUMA policy for the VMA */
#endif
struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+ seqcount_t vm_sequence;
+#endif
};
struct core_thread {
diff --git a/mm/memory.c b/mm/memory.c
index 4fa2c30..188722e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1285,6 +1285,7 @@
unsigned long next;
BUG_ON(addr >= end);
+ vm_write_begin(vma);
tlb_start_vma(tlb, vma);
pgd = pgd_offset(vma->vm_mm, addr);
do {
@@ -1294,6 +1295,7 @@
next = zap_pud_range(tlb, vma, pgd, addr, next, details);
} while (pgd++, addr = next, addr != end);
tlb_end_vma(tlb, vma);
+ vm_write_end(vma);
}
diff --git a/mm/mmap.c b/mm/mmap.c
index 7eee09a..b6a3f47 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -690,6 +690,30 @@
long adjust_next = 0;
int remove_next = 0;
+ /*
+ * Why using vm_raw_write*() functions here to avoid lockdep's warning ?
+ *
+ * Locked is complaining about a theoretical lock dependency, involving
+ * 3 locks:
+ * mapping->i_mmap_rwsem --> vma->vm_sequence --> fs_reclaim
+ *
+ * Here are the major path leading to this dependency :
+ * 1. __vma_adjust() mmap_sem -> vm_sequence -> i_mmap_rwsem
+ * 2. move_vmap() mmap_sem -> vm_sequence -> fs_reclaim
+ * 3. __alloc_pages_nodemask() fs_reclaim -> i_mmap_rwsem
+ * 4. unmap_mapping_range() i_mmap_rwsem -> vm_sequence
+ *
+ * So there is no way to solve this easily, especially because in
+ * unmap_mapping_range() the i_mmap_rwsem is grab while the impacted
+ * VMAs are not yet known.
+ * However, the way the vm_seq is used is guarantying that we will
+ * never block on it since we just check for its value and never wait
+ * for it to move, see vma_has_changed() and handle_speculative_fault().
+ */
+ vm_raw_write_begin(vma);
+ if (next)
+ vm_raw_write_begin(next);
+
if (next && !insert) {
struct vm_area_struct *exporter = NULL, *importer = NULL;
@@ -900,6 +924,7 @@
anon_vma_merge(vma, next);
mm->map_count--;
mpol_put(vma_policy(next));
+ vm_raw_write_end(next);
kmem_cache_free(vm_area_cachep, next);
/*
* In mprotect's case 6 (see comments on vma_merge),
@@ -914,6 +939,8 @@
* "vma->vm_next" gap must be updated.
*/
next = vma->vm_next;
+ if (next)
+ vm_raw_write_begin(next);
} else {
/*
* For the scope of the comment "next" and
@@ -960,6 +987,10 @@
if (insert && file)
uprobe_mmap(insert);
+ if (next && next != vma)
+ vm_raw_write_end(next);
+ vm_raw_write_end(vma);
+
validate_mm(mm);
return 0;