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author | Dave Airlie <airlied@redhat.com> | 2023-08-24 07:26:06 +1000 |
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committer | Dave Airlie <airlied@redhat.com> | 2023-08-24 07:26:06 +1000 |
commit | fdebffeba8b877368ddcc139c26278c1c97931a4 (patch) | |
tree | 5ebf85a3e26d55ea388aa7a8608222205a4d59ba /include/linux/mm.h | |
parent | cacaeb27ade4b793c456179bb6eda4592d206cd8 (diff) | |
parent | 706a741595047797872e669b3101429ab8d378ef (diff) | |
download | linux-stable-fdebffeba8b877368ddcc139c26278c1c97931a4.tar.gz linux-stable-fdebffeba8b877368ddcc139c26278c1c97931a4.tar.bz2 linux-stable-fdebffeba8b877368ddcc139c26278c1c97931a4.zip |
BackMerge tag 'v6.5-rc7' into drm-next
Linux 6.5-rc7
This is needed for the CI stuff and the msm pull has fixes in it.
Signed-off-by: Dave Airlie <airlied@redhat.com>
Diffstat (limited to 'include/linux/mm.h')
-rw-r--r-- | include/linux/mm.h | 29 |
1 files changed, 23 insertions, 6 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index 2dd73e4f3d8e..406ab9ea818f 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -641,8 +641,14 @@ static inline void vma_numab_state_free(struct vm_area_struct *vma) {} */ static inline bool vma_start_read(struct vm_area_struct *vma) { - /* Check before locking. A race might cause false locked result. */ - if (vma->vm_lock_seq == READ_ONCE(vma->vm_mm->mm_lock_seq)) + /* + * Check before locking. A race might cause false locked result. + * We can use READ_ONCE() for the mm_lock_seq here, and don't need + * ACQUIRE semantics, because this is just a lockless check whose result + * we don't rely on for anything - the mm_lock_seq read against which we + * need ordering is below. + */ + if (READ_ONCE(vma->vm_lock_seq) == READ_ONCE(vma->vm_mm->mm_lock_seq)) return false; if (unlikely(down_read_trylock(&vma->vm_lock->lock) == 0)) @@ -653,8 +659,13 @@ static inline bool vma_start_read(struct vm_area_struct *vma) * False unlocked result is impossible because we modify and check * vma->vm_lock_seq under vma->vm_lock protection and mm->mm_lock_seq * modification invalidates all existing locks. + * + * We must use ACQUIRE semantics for the mm_lock_seq so that if we are + * racing with vma_end_write_all(), we only start reading from the VMA + * after it has been unlocked. + * This pairs with RELEASE semantics in vma_end_write_all(). */ - if (unlikely(vma->vm_lock_seq == READ_ONCE(vma->vm_mm->mm_lock_seq))) { + if (unlikely(vma->vm_lock_seq == smp_load_acquire(&vma->vm_mm->mm_lock_seq))) { up_read(&vma->vm_lock->lock); return false; } @@ -676,7 +687,7 @@ static bool __is_vma_write_locked(struct vm_area_struct *vma, int *mm_lock_seq) * current task is holding mmap_write_lock, both vma->vm_lock_seq and * mm->mm_lock_seq can't be concurrently modified. */ - *mm_lock_seq = READ_ONCE(vma->vm_mm->mm_lock_seq); + *mm_lock_seq = vma->vm_mm->mm_lock_seq; return (vma->vm_lock_seq == *mm_lock_seq); } @@ -688,7 +699,13 @@ static inline void vma_start_write(struct vm_area_struct *vma) return; down_write(&vma->vm_lock->lock); - vma->vm_lock_seq = mm_lock_seq; + /* + * We should use WRITE_ONCE() here because we can have concurrent reads + * from the early lockless pessimistic check in vma_start_read(). + * We don't really care about the correctness of that early check, but + * we should use WRITE_ONCE() for cleanliness and to keep KCSAN happy. + */ + WRITE_ONCE(vma->vm_lock_seq, mm_lock_seq); up_write(&vma->vm_lock->lock); } @@ -702,7 +719,7 @@ static inline bool vma_try_start_write(struct vm_area_struct *vma) if (!down_write_trylock(&vma->vm_lock->lock)) return false; - vma->vm_lock_seq = mm_lock_seq; + WRITE_ONCE(vma->vm_lock_seq, mm_lock_seq); up_write(&vma->vm_lock->lock); return true; } |