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ANDROID: mm: use raw seqcount variants in vm_write_*

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write_seqcount_begin expects to be called from a non-preemptible
context to avoid preemption by a read section that can spin due
to an odd value. But the readers of vm_sequence never retries and
thus writers need not disable preemption. Use the non-lockdep
variant as lockdep checks are now in-built to write_seqcount_begin.

Bug: 161210518
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
Change-Id: If4f0cddd7f0a79136495060d4acc1702abb46817
Git-commit: c9201630e8a53106406516ba40862e637c324480
Git-repo: https://android.googlesource.com/kernel/common/
Signed-off-by: Srinivasarao Pathipati <quic_spathi@quicinc.com>
This commit is contained in:
Vinayak Menon 2021-01-15 19:52:40 +05:30 • committed by Gerrit - the friendly Code Review server
commit f2c1ef71ed
3 changed files with 18 additions and 57 deletions
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29
include/linux/mm.h
View file

@ -1541,22 +1541,13 @@ int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
#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)
{
/*
* The reads never spins and preemption
* disablement is not required.
*/
raw_write_seqcount_begin(&vma->vm_sequence);
}
static inline void vm_raw_write_end(struct vm_area_struct *vma)
static inline void vm_write_end(struct vm_area_struct *vma)
{
raw_write_seqcount_end(&vma->vm_sequence);
}
@ -1564,19 +1555,9 @@ static inline void vm_raw_write_end(struct vm_area_struct *vma)
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);

38
mm/mmap.c
View file

@ -766,29 +766,9 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
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);
vm_write_begin(vma);
if (next)
vm_raw_write_begin(next);
vm_write_begin(next);
if (next && !insert) {
struct vm_area_struct *exporter = NULL, *importer = NULL;
@ -872,8 +852,8 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
error = anon_vma_clone(importer, exporter);
if (error) {
if (next && next != vma)
vm_raw_write_end(next);
vm_raw_write_end(vma);
vm_write_end(next);
vm_write_end(vma);
return error;
}
}
@ -1002,7 +982,7 @@ again:
if (next->anon_vma)
anon_vma_merge(vma, next);
mm->map_count--;
vm_raw_write_end(next);
vm_write_end(next);
put_vma(next);
/*
* In mprotect's case 6 (see comments on vma_merge),
@ -1018,7 +998,7 @@ again:
*/
next = vma->vm_next;
if (next)
vm_raw_write_begin(next);
vm_write_begin(next);
} else {
/*
* For the scope of the comment "next" and
@ -1066,9 +1046,9 @@ again:
uprobe_mmap(insert);
if (next && next != vma)
vm_raw_write_end(next);
vm_write_end(next);
if (!keep_locked)
vm_raw_write_end(vma);
vm_write_end(vma);
validate_mm(mm);
@ -3412,7 +3392,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
* that we protect it right now, and let the caller unprotect
* it once the move is done.
*/
vm_raw_write_begin(new_vma);
vm_write_begin(new_vma);
vma_link(mm, new_vma, prev, rb_link, rb_parent);
*need_rmap_locks = false;
}

8
mm/mremap.c
View file

@ -363,7 +363,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
* to be mapped in our back while we are copying the PTEs.
*/
if (vma != new_vma)
vm_raw_write_begin(vma);
vm_write_begin(vma);
moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
need_rmap_locks);
@ -382,7 +382,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
true);
if (vma != new_vma)
vm_raw_write_end(vma);
vm_write_end(vma);
vma = new_vma;
old_len = new_len;
old_addr = new_addr;
@ -392,9 +392,9 @@ static unsigned long move_vma(struct vm_area_struct *vma,
arch_remap(mm, old_addr, old_addr + old_len,
new_addr, new_addr + new_len);
if (vma != new_vma)
vm_raw_write_end(vma);
vm_write_end(vma);
}
vm_raw_write_end(new_vma);
vm_write_end(new_vma);
/* Conceal VM_ACCOUNT so old reservation is not undone */
if (vm_flags & VM_ACCOUNT) {