For lockless /proc/pid/maps reading we have to ensure all the fields used when generating the output are RCU-safe. The only pointer fields in vm_area_struct which are used to generate that file's output are vm_file and anon_name. vm_file is RCU-safe but anon_name is not. Make anon_name RCU-safe as well. Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> --- include/linux/mm_inline.h | 10 +++++++++- include/linux/mm_types.h | 3 ++- mm/madvise.c | 30 ++++++++++++++++++++++++++---- 3 files changed, 37 insertions(+), 6 deletions(-) diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h index f4fe593c1400..bbdb0ca857f1 100644 --- a/include/linux/mm_inline.h +++ b/include/linux/mm_inline.h @@ -389,7 +389,7 @@ static inline void dup_anon_vma_name(struct vm_area_struct *orig_vma, struct anon_vma_name *anon_name = anon_vma_name(orig_vma); if (anon_name) - new_vma->anon_name = anon_vma_name_reuse(anon_name); + rcu_assign_pointer(new_vma->anon_name, anon_vma_name_reuse(anon_name)); } static inline void free_anon_vma_name(struct vm_area_struct *vma) @@ -411,6 +411,8 @@ static inline bool anon_vma_name_eq(struct anon_vma_name *anon_name1, !strcmp(anon_name1->name, anon_name2->name); } +struct anon_vma_name *anon_vma_name_get_rcu(struct vm_area_struct *vma); + #else /* CONFIG_ANON_VMA_NAME */ static inline void anon_vma_name_get(struct anon_vma_name *anon_name) {} static inline void anon_vma_name_put(struct anon_vma_name *anon_name) {} @@ -424,6 +426,12 @@ static inline bool anon_vma_name_eq(struct anon_vma_name *anon_name1, return true; } +static inline +struct anon_vma_name *anon_vma_name_get_rcu(struct vm_area_struct *vma) +{ + return NULL; +} + #endif /* CONFIG_ANON_VMA_NAME */ static inline void init_tlb_flush_pending(struct mm_struct *mm) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 8b611e13153e..bbe1223cd992 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -545,6 +545,7 @@ struct vm_userfaultfd_ctx {}; struct anon_vma_name { struct kref kref; + struct rcu_head rcu; /* The name needs to be at the end because it is dynamically sized. */ char name[]; }; @@ -699,7 +700,7 @@ struct vm_area_struct { * terminated string containing the name given to the vma, or NULL if * unnamed. Serialized by mmap_lock. Use anon_vma_name to access. */ - struct anon_vma_name *anon_name; + struct anon_vma_name __rcu *anon_name; #endif #ifdef CONFIG_SWAP atomic_long_t swap_readahead_info; diff --git a/mm/madvise.c b/mm/madvise.c index 912155a94ed5..0f222d464254 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -88,14 +88,15 @@ void anon_vma_name_free(struct kref *kref) { struct anon_vma_name *anon_name = container_of(kref, struct anon_vma_name, kref); - kfree(anon_name); + kfree_rcu(anon_name, rcu); } struct anon_vma_name *anon_vma_name(struct vm_area_struct *vma) { mmap_assert_locked(vma->vm_mm); - return vma->anon_name; + return rcu_dereference_protected(vma->anon_name, + rwsem_is_locked(&vma->vm_mm->mmap_lock)); } /* mmap_lock should be write-locked */ @@ -105,7 +106,7 @@ static int replace_anon_vma_name(struct vm_area_struct *vma, struct anon_vma_name *orig_name = anon_vma_name(vma); if (!anon_name) { - vma->anon_name = NULL; + rcu_assign_pointer(vma->anon_name, NULL); anon_vma_name_put(orig_name); return 0; } @@ -113,11 +114,32 @@ static int replace_anon_vma_name(struct vm_area_struct *vma, if (anon_vma_name_eq(orig_name, anon_name)) return 0; - vma->anon_name = anon_vma_name_reuse(anon_name); + rcu_assign_pointer(vma->anon_name, anon_vma_name_reuse(anon_name)); anon_vma_name_put(orig_name); return 0; } + +/* + * Returned anon_vma_name is stable due to elevated refcount but not guaranteed + * to be assigned to the original VMA after the call. + */ +struct anon_vma_name *anon_vma_name_get_rcu(struct vm_area_struct *vma) +{ + struct anon_vma_name __rcu *anon_name; + + WARN_ON_ONCE(!rcu_read_lock_held()); + + anon_name = rcu_dereference(vma->anon_name); + if (!anon_name) + return NULL; + + if (unlikely(!kref_get_unless_zero(&anon_name->kref))) + return NULL; + + return anon_name; +} + #else /* CONFIG_ANON_VMA_NAME */ static int replace_anon_vma_name(struct vm_area_struct *vma, struct anon_vma_name *anon_name) -- 2.43.0.429.g432eaa2c6b-goog