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Message-ID: <CAJuCfpGsDOewHUEK4R11hTxMTh_QE0MPQno2C+E_WMCScTsqcw@mail.gmail.com>
Date: Tue, 22 Feb 2022 07:51:56 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Michal Hocko <mhocko@...e.com>
Cc: akpm@...ux-foundation.org, ccross@...gle.com,
sumit.semwal@...aro.org, dave.hansen@...el.com,
keescook@...omium.org, willy@...radead.org,
kirill.shutemov@...ux.intel.com, vbabka@...e.cz,
hannes@...xchg.org, ebiederm@...ssion.com, brauner@...nel.org,
legion@...nel.org, ran.xiaokai@....com.cn, sashal@...nel.org,
chris.hyser@...cle.com, dave@...olabs.net, pcc@...gle.com,
caoxiaofeng@...ong.com, david@...hat.com, gorcunov@...il.com,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
kernel-team@...roid.com
Subject: Re: [PATCH 1/3] mm: refactor vm_area_struct::anon_vma_name usage code
On Tue, Feb 22, 2022 at 12:51 AM Michal Hocko <mhocko@...e.com> wrote:
>
> On Mon 21-02-22 21:40:23, Suren Baghdasaryan wrote:
> > Avoid mixing strings and their anon_vma_name referenced pointers
> > by using struct anon_vma_name whenever possible. This simplifies
> > the code and allows easier sharing of anon_vma_name structures when
> > they represent the same name.
>
> I just diffed this to my half baked proposal to see for changes. Let me
> comment on those as this will be very likely easier to review than
> looking at the new code.
Thanks for the effort!
>
> > diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
> > index 17c20597e244..70b619442d56 100644
> > --- a/include/linux/mm_inline.h
> > +++ b/include/linux/mm_inline.h
> > @@ -140,61 +140,73 @@ static __always_inline void del_page_from_lru_list(struct page *page,
> >
> > #ifdef CONFIG_ANON_VMA_NAME
> > /*
> > - * mmap_lock should be read-locked when calling vma_anon_name() and while using
> > - * the returned pointer.
> > + * mmap_lock should be read-locked when calling vma_anon_name(). Caller should
> > + * either keep holding the lock while using the returned pointer or it should
> > + * raise anon_vma_name refcount before releasing the lock.
> > */
> > -extern const char *vma_anon_name(struct vm_area_struct *vma);
> > +extern struct anon_vma_name *vma_anon_name(struct vm_area_struct *vma);
>
> OK, I can see some reason to force final users of the name to dig it out
> of the struct but I would recommend unifying the naming. vma_anon_name
> makes sense if you are providing the real name. But for all functions
> which operate on anon_vma_name I would stick with anon_vma_$FOO.
> You seem to be inconsistent in that regards. E.g. dup_vma_anon_name
> but anon_vma_name_{get,put}. I do not really care one way or the other
> but please make then consistent.
Ack. Will change the names the way you suggested.
>
> > +extern struct anon_vma_name *anon_vma_name_alloc(const char *name);
> >
> > -static inline void anon_vma_name_get(struct anon_vma_name *name)
> > +/* mmap_lock should be read-locked */
> > +static inline void anon_vma_name_get(struct anon_vma_name *anon_name)
> > {
> > - if (!name)
> > - return;
> > -
> > - kref_get(&name->kref);
> > + if (anon_name)
> > + kref_get(&anon_name->kref);
> > }
> >
> > -void vma_anon_name_free(struct kref *kref);
> > -static inline void anon_vma_name_put(struct anon_vma_name *name)
> > -{
> > - if (!name)
> > - return;
> > -
> > - kref_put(&name->kref, vma_anon_name_free);
> > -}
> > +extern void anon_vma_name_put(struct anon_vma_name *anon_name);
>
> I would keep get and put close together. It is just easier to follow the
> code that way. But no strong preference here.
Ack.
>
> > -static inline bool anon_vma_name_eq(struct anon_vma_name *name1, struct anon_vma_name *name2)
> > +static inline void dup_vma_anon_name(struct vm_area_struct *orig_vma,
>
> dup_anon_vma_name
>
> > static inline void free_vma_anon_name(struct vm_area_struct *vma)
>
> free_anon_vma_name
>
> > {
> > - anon_vma_name_put(vma->anon_name);
> > + /* Can't use vma_anon_name because vma->vm_mm might not be held */
>
> I do not follow. I guess you meant to say that mmap_lock might not be
> held but why is that important in this context when the vma goes away?
> Nobody can be copying anon_name from it?
I wanted to explain why I can't use vma_anon_name and have to check
vma->vm_file directly instead. vma_anon_name has
mmap_assert_locked(vma->vm_mm) and will generate a warning if called
without mmap_lock being held. I will write a more descriptive comment
here.
>
> > + if (!vma->vm_file)
> > + anon_vma_name_put(vma->anon_name);
> > }
>
> [...]
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index f2f8065f67c1..f81d62d8ce9b 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -70,6 +70,9 @@ struct anon_vma_name *anon_vma_name_alloc(const char *name)
> > struct anon_vma_name *anon_name;
> > size_t count;
> >
> > + if (!name)
> > + return NULL;
> > +
>
> This is not really needed.
True. Will remove.
>
> > /* Add 1 for NUL terminator at the end of the anon_name->name */
> > count = strlen(name) + 1;
> > anon_name = kmalloc(struct_size(anon_name, name, count), GFP_KERNEL);
>
> [...]
> > @@ -947,6 +956,7 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
> > {
> > int error;
> > unsigned long new_flags = vma->vm_flags;
> > + struct anon_vma_name *anon_name;
> >
> > switch (behavior) {
> > case MADV_REMOVE:
> > @@ -1011,8 +1021,9 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
> > break;
> > }
> >
> > + anon_name = vma_anon_name(vma);
> > error = madvise_update_vma(vma, prev, start, end, new_flags,
> > - vma->anon_name);
> > + anon_name);
> >
> > out:
>
> You can use vma_anon_name directly, no need to add 2 more lines of code
> ;)
Ack.
>
> > @@ -1237,8 +1248,8 @@ int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
> > if (end == start)
> > return 0;
> >
> > - return madvise_walk_vmas(mm, start, end, (unsigned long)name,
> > - madvise_vma_anon_name);
> > + return madvise_walk_vmas(mm, start, end, (unsigned long)anon_name,
> > + madvise_vma_anon_name);
>
> whitespace noise
Ack.
>
> Other that that nothing else really jumped at me. Here is a diff I
> propose on top of this patch. Mostly naming unification and you will get
> 8 less lines in the end ;)
Thanks. Will be incorporated into the next revision.
> ---
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 5bfcf24493ac..2c48b1eaaa9c 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -327,7 +327,7 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
> goto done;
> }
>
> - anon_name = vma_anon_name(vma);
> + anon_name = anon_vma_name(vma);
> if (anon_name) {
> seq_pad(m, ' ');
> seq_printf(m, "[anon:%s]", anon_name->name);
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index e26b10132d47..8e03b3d3f5fa 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -878,7 +878,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
> new_flags, vma->anon_vma,
> vma->vm_file, vma->vm_pgoff,
> vma_policy(vma),
> - NULL_VM_UFFD_CTX, vma_anon_name(vma));
> + NULL_VM_UFFD_CTX, anon_vma_name(vma));
> if (prev)
> vma = prev;
> else
> @@ -1438,7 +1438,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> vma->anon_vma, vma->vm_file, vma->vm_pgoff,
> vma_policy(vma),
> ((struct vm_userfaultfd_ctx){ ctx }),
> - vma_anon_name(vma));
> + anon_vma_name(vma));
> if (prev) {
> vma = prev;
> goto next;
> @@ -1615,7 +1615,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> prev = vma_merge(mm, prev, start, vma_end, new_flags,
> vma->anon_vma, vma->vm_file, vma->vm_pgoff,
> vma_policy(vma),
> - NULL_VM_UFFD_CTX, vma_anon_name(vma));
> + NULL_VM_UFFD_CTX, anon_vma_name(vma));
> if (prev) {
> vma = prev;
> goto next;
> diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
> index 70b619442d56..60b48e4a5560 100644
> --- a/include/linux/mm_inline.h
> +++ b/include/linux/mm_inline.h
> @@ -140,11 +140,11 @@ static __always_inline void del_page_from_lru_list(struct page *page,
>
> #ifdef CONFIG_ANON_VMA_NAME
> /*
> - * mmap_lock should be read-locked when calling vma_anon_name(). Caller should
> + * mmap_lock should be read-locked when calling anon_vma_name(). Caller should
> * either keep holding the lock while using the returned pointer or it should
> * raise anon_vma_name refcount before releasing the lock.
> */
> -extern struct anon_vma_name *vma_anon_name(struct vm_area_struct *vma);
> +extern struct anon_vma_name *anon_vma_name(struct vm_area_struct *vma);
> extern struct anon_vma_name *anon_vma_name_alloc(const char *name);
>
> /* mmap_lock should be read-locked */
> @@ -156,10 +156,10 @@ static inline void anon_vma_name_get(struct anon_vma_name *anon_name)
>
> extern void anon_vma_name_put(struct anon_vma_name *anon_name);
>
> -static inline void dup_vma_anon_name(struct vm_area_struct *orig_vma,
> +static inline void dup_anon_vma_name(struct vm_area_struct *orig_vma,
> struct vm_area_struct *new_vma)
> {
> - struct anon_vma_name *anon_name = vma_anon_name(orig_vma);
> + struct anon_vma_name *anon_name = anon_vma_name(orig_vma);
>
> if (anon_name) {
> anon_vma_name_get(anon_name);
> @@ -167,7 +167,7 @@ static inline void dup_vma_anon_name(struct vm_area_struct *orig_vma,
> }
> }
>
> -static inline void free_vma_anon_name(struct vm_area_struct *vma)
> +static inline void free_anon_vma_name(struct vm_area_struct *vma)
> {
> /* Can't use vma_anon_name because vma->vm_mm might not be held */
> if (!vma->vm_file)
> @@ -185,7 +185,7 @@ static inline bool anon_vma_name_eq(struct anon_vma_name *anon_name1,
> }
>
> #else /* CONFIG_ANON_VMA_NAME */
> -static inline struct anon_vma_name *vma_anon_name(struct vm_area_struct *vma)
> +static inline struct anon_vma_name *anon_vma_name(struct vm_area_struct *vma)
> {
> return NULL;
> }
> @@ -197,9 +197,9 @@ static inline struct anon_vma_name *anon_vma_name_alloc(const char *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) {}
> -static inline void dup_vma_anon_name(struct vm_area_struct *orig_vma,
> +static inline void dup_anon_vma_name(struct vm_area_struct *orig_vma,
> struct vm_area_struct *new_vma) {}
> -static inline void free_vma_anon_name(struct vm_area_struct *vma) {}
> +static inline void free_anon_vma_name(struct vm_area_struct *vma) {}
>
> static inline bool anon_vma_name_eq(struct anon_vma_name *anon_name1,
> struct anon_vma_name *anon_name2)
> diff --git a/kernel/fork.c b/kernel/fork.c
> index d75a528f7b21..e7dc5c29212c 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -366,14 +366,14 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
> *new = data_race(*orig);
> INIT_LIST_HEAD(&new->anon_vma_chain);
> new->vm_next = new->vm_prev = NULL;
> - dup_vma_anon_name(orig, new);
> + dup_anon_vma_name(orig, new);
> }
> return new;
> }
>
> void vm_area_free(struct vm_area_struct *vma)
> {
> - free_vma_anon_name(vma);
> + free_anon_vma_name(vma);
> kmem_cache_free(vm_area_cachep, vma);
> }
>
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 60c3f9eac9eb..c150aa335eeb 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2279,7 +2279,7 @@ static int prctl_set_vma(unsigned long opt, unsigned long addr,
> {
> struct mm_struct *mm = current->mm;
> const char __user *uname;
> - struct anon_vma_name *anon_name;
> + struct anon_vma_name *anon_name = NULL;
> int error;
>
> switch (opt) {
> @@ -2304,9 +2304,6 @@ static int prctl_set_vma(unsigned long opt, unsigned long addr,
> if (!anon_name)
> return -ENOMEM;
>
> - } else {
> - /* Reset the name */
> - anon_name = NULL;
> }
>
> mmap_write_lock(mm);
> diff --git a/mm/madvise.c b/mm/madvise.c
> index f81d62d8ce9b..f23c66d15bd5 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -70,9 +70,6 @@ struct anon_vma_name *anon_vma_name_alloc(const char *name)
> struct anon_vma_name *anon_name;
> size_t count;
>
> - if (!name)
> - return NULL;
> -
> /* Add 1 for NUL terminator at the end of the anon_name->name */
> count = strlen(name) + 1;
> anon_name = kmalloc(struct_size(anon_name, name, count), GFP_KERNEL);
> @@ -84,7 +81,7 @@ struct anon_vma_name *anon_vma_name_alloc(const char *name)
> return anon_name;
> }
>
> -struct anon_vma_name *vma_anon_name(struct vm_area_struct *vma)
> +struct anon_vma_name *anon_vma_name(struct vm_area_struct *vma)
> {
> mmap_assert_locked(vma->vm_mm);
>
> @@ -108,10 +105,10 @@ void anon_vma_name_put(struct anon_vma_name *anon_name)
> }
>
> /* mmap_lock should be write-locked */
> -static int replace_vma_anon_name(struct vm_area_struct *vma,
> +static int replace_anon_vma_name(struct vm_area_struct *vma,
> struct anon_vma_name *anon_name)
> {
> - struct anon_vma_name *orig_name = vma_anon_name(vma);
> + struct anon_vma_name *orig_name = anon_vma_name(vma);
>
> if (!anon_name) {
> vma->anon_name = NULL;
> @@ -129,7 +126,7 @@ static int replace_vma_anon_name(struct vm_area_struct *vma,
> return 0;
> }
> #else /* CONFIG_ANON_VMA_NAME */
> -static int replace_vma_anon_name(struct vm_area_struct *vma,
> +static int replace_anon_vma_name(struct vm_area_struct *vma,
> struct anon_vma_name *anon_name)
> {
> if (anon_name)
> @@ -151,7 +148,7 @@ static int madvise_update_vma(struct vm_area_struct *vma,
> int error;
> pgoff_t pgoff;
>
> - if (new_flags == vma->vm_flags && anon_vma_name_eq(vma_anon_name(vma), anon_name)) {
> + if (new_flags == vma->vm_flags && anon_vma_name_eq(anon_vma_name(vma), anon_name)) {
> *prev = vma;
> return 0;
> }
> @@ -189,7 +186,7 @@ static int madvise_update_vma(struct vm_area_struct *vma,
> */
> vma->vm_flags = new_flags;
> if (!vma->vm_file) {
> - error = replace_vma_anon_name(vma, anon_name);
> + error = replace_anon_vma_name(vma, anon_name);
> if (error)
> return error;
> }
> @@ -956,7 +953,6 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
> {
> int error;
> unsigned long new_flags = vma->vm_flags;
> - struct anon_vma_name *anon_name;
>
> switch (behavior) {
> case MADV_REMOVE:
> @@ -1021,9 +1017,8 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
> break;
> }
>
> - anon_name = vma_anon_name(vma);
> error = madvise_update_vma(vma, prev, start, end, new_flags,
> - anon_name);
> + anon_vma_name(vma));
>
> out:
> /*
> @@ -1248,8 +1243,8 @@ int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
> if (end == start)
> return 0;
>
> - return madvise_walk_vmas(mm, start, end, (unsigned long)anon_name,
> - madvise_vma_anon_name);
> + return madvise_walk_vmas(mm, start, end, (unsigned long)anon_name,
> + madvise_vma_anon_name);
> }
> #endif /* CONFIG_ANON_VMA_NAME */
> /*
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 028e8dd82b44..69284d3b5e53 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -814,7 +814,7 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
> prev = vma_merge(mm, prev, vmstart, vmend, vma->vm_flags,
> vma->anon_vma, vma->vm_file, pgoff,
> new_pol, vma->vm_userfaultfd_ctx,
> - vma_anon_name(vma));
> + anon_vma_name(vma));
> if (prev) {
> vma = prev;
> next = vma->vm_next;
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 8f584eddd305..25934e7db3e1 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -512,7 +512,7 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
> pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
> *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
> vma->vm_file, pgoff, vma_policy(vma),
> - vma->vm_userfaultfd_ctx, vma_anon_name(vma));
> + vma->vm_userfaultfd_ctx, anon_vma_name(vma));
> if (*prev) {
> vma = *prev;
> goto success;
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 80d2ae204a98..ad6a1fffee91 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1049,7 +1049,7 @@ static inline int is_mergeable_vma(struct vm_area_struct *vma,
> return 0;
> if (!is_mergeable_vm_userfaultfd_ctx(vma, vm_userfaultfd_ctx))
> return 0;
> - if (!anon_vma_name_eq(vma_anon_name(vma), anon_name))
> + if (!anon_vma_name_eq(anon_vma_name(vma), anon_name))
> return 0;
> return 1;
> }
> @@ -3255,7 +3255,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
> return NULL; /* should never get here */
> new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
> vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
> - vma->vm_userfaultfd_ctx, vma_anon_name(vma));
> + vma->vm_userfaultfd_ctx, anon_vma_name(vma));
> if (new_vma) {
> /*
> * Source vma may have been merged into new_vma
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index 0138dfcdb1d8..9fce6860cdab 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -464,7 +464,7 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
> pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
> *pprev = vma_merge(mm, *pprev, start, end, newflags,
> vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
> - vma->vm_userfaultfd_ctx, vma_anon_name(vma));
> + vma->vm_userfaultfd_ctx, anon_vma_name(vma));
> if (*pprev) {
> vma = *pprev;
> VM_WARN_ON((vma->vm_flags ^ newflags) & ~VM_SOFTDIRTY);
> --
> Michal Hocko
> SUSE Labs
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