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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
parent 4bd53b8750
commit 1091e4b2ff
3 changed files with 18 additions and 57 deletions
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29
include/linux/mm.h
View file

@ -1498,22 +1498,13 @@ int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
#ifdef CONFIG_SPECULATIVE_PAGE_FAULT #ifdef CONFIG_SPECULATIVE_PAGE_FAULT
static inline void vm_write_begin(struct vm_area_struct *vma) static inline void vm_write_begin(struct vm_area_struct *vma)
{ {
write_seqcount_begin(&vma->vm_sequence); /*
} * The reads never spins and preemption
static inline void vm_write_begin_nested(struct vm_area_struct *vma, * disablement is not required.
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); 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); raw_write_seqcount_end(&vma->vm_sequence);
} }
@ -1521,19 +1512,9 @@ 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(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_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 */ #endif /* CONFIG_SPECULATIVE_PAGE_FAULT */
extern void truncate_pagecache(struct inode *inode, loff_t new); extern void truncate_pagecache(struct inode *inode, loff_t new);

38
mm/mmap.c
View file

@ -735,29 +735,9 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
long adjust_next = 0; long adjust_next = 0;
int remove_next = 0; int remove_next = 0;
/* vm_write_begin(vma);
* 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) if (next)
vm_raw_write_begin(next); vm_write_begin(next);
if (next && !insert) { if (next && !insert) {
struct vm_area_struct *exporter = NULL, *importer = NULL; struct vm_area_struct *exporter = NULL, *importer = NULL;
@ -841,8 +821,8 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
error = anon_vma_clone(importer, exporter); error = anon_vma_clone(importer, exporter);
if (error) { if (error) {
if (next && next != vma) if (next && next != vma)
vm_raw_write_end(next); vm_write_end(next);
vm_raw_write_end(vma); vm_write_end(vma);
return error; return error;
} }
} }
@ -971,7 +951,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
if (next->anon_vma) if (next->anon_vma)
anon_vma_merge(vma, next); anon_vma_merge(vma, next);
mm->map_count--; mm->map_count--;
vm_raw_write_end(next); vm_write_end(next);
put_vma(next); put_vma(next);
/* /*
* In mprotect's case 6 (see comments on vma_merge), * In mprotect's case 6 (see comments on vma_merge),
@ -987,7 +967,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
*/ */
next = vma->vm_next; next = vma->vm_next;
if (next) if (next)
vm_raw_write_begin(next); vm_write_begin(next);
} else { } else {
/* /*
* For the scope of the comment "next" and * For the scope of the comment "next" and
@ -1035,9 +1015,9 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
uprobe_mmap(insert); uprobe_mmap(insert);
if (next && next != vma) if (next && next != vma)
vm_raw_write_end(next); vm_write_end(next);
if (!keep_locked) if (!keep_locked)
vm_raw_write_end(vma); vm_write_end(vma);
validate_mm(mm); validate_mm(mm);
@ -3348,7 +3328,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
* that we protect it right now, and let the caller unprotect * that we protect it right now, and let the caller unprotect
* it once the move is done. * 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); vma_link(mm, new_vma, prev, rb_link, rb_parent);
*need_rmap_locks = false; *need_rmap_locks = false;
} }

8
mm/mremap.c
View file

@ -300,7 +300,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
* to be mapped in our back while we are copying the PTEs. * to be mapped in our back while we are copying the PTEs.
*/ */
if (vma != new_vma) 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, moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
need_rmap_locks); need_rmap_locks);
@ -319,7 +319,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
move_page_tables(new_vma, new_addr, vma, old_addr, moved_len, move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
true); true);
if (vma != new_vma) if (vma != new_vma)
vm_raw_write_end(vma); vm_write_end(vma);
vma = new_vma; vma = new_vma;
old_len = new_len; old_len = new_len;
old_addr = new_addr; old_addr = new_addr;
@ -329,9 +329,9 @@ static unsigned long move_vma(struct vm_area_struct *vma,
arch_remap(mm, old_addr, old_addr + old_len, arch_remap(mm, old_addr, old_addr + old_len,
new_addr, new_addr + new_len); new_addr, new_addr + new_len);
if (vma != new_vma) 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 */ /* Conceal VM_ACCOUNT so old reservation is not undone */
if (vm_flags & VM_ACCOUNT) { if (vm_flags & VM_ACCOUNT) {