REGRESSION: [PATCHv2 2/2] mm: Drop unneeded ->vm_ops checks

From: Marcel Ziswiler
Date: Mon Jul 16 2018 - 09:30:49 EST

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On Thu, 2018-07-12 at 17:56 +0300, Kirill A. Shutemov wrote:
> We now have all VMAs with ->vm_ops set and don't need to check it for
> NULL everywhere.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
> fs/binfmt_elf.c | 2 +-
> fs/kernfs/file.c | 20 +-------------------
> fs/proc/task_mmu.c | 2 +-
> kernel/events/core.c | 2 +-
> kernel/fork.c | 2 +-
> mm/gup.c | 2 +-
> mm/hugetlb.c | 2 +-
> mm/memory.c | 12 ++++++------
> mm/mempolicy.c | 10 +++++-----
> mm/mmap.c | 14 +++++++-------
> mm/mremap.c | 2 +-
> mm/nommu.c | 4 ++--
> 12 files changed, 28 insertions(+), 46 deletions(-)
>
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 0ac456b52bdd..4f171cf21bc2 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -1302,7 +1302,7 @@ static bool always_dump_vma(struct
> vm_area_struct *vma)
> * Assume that all vmas with a .name op should always be
> dumped.
> * If this changes, a new vm_ops field can easily be added.
> */
> - if (vma->vm_ops && vma->vm_ops->name && vma->vm_ops-
> >name(vma))
> + if (vma->vm_ops->name && vma->vm_ops->name(vma))
> return true;
>
> /*
> diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
> index 2015d8c45e4a..945c3d306d8f 100644
> --- a/fs/kernfs/file.c
> +++ b/fs/kernfs/file.c
> @@ -336,9 +336,6 @@ static void kernfs_vma_open(struct vm_area_struct
> *vma)
> struct file *file = vma->vm_file;
> struct kernfs_open_file *of = kernfs_of(file);
>
> - if (!of->vm_ops)
> - return;
> -
> if (!kernfs_get_active(of->kn))
> return;
>
> @@ -354,9 +351,6 @@ static vm_fault_t kernfs_vma_fault(struct
> vm_fault *vmf)
> struct kernfs_open_file *of = kernfs_of(file);
> vm_fault_t ret;
>
> - if (!of->vm_ops)
> - return VM_FAULT_SIGBUS;
> -
> if (!kernfs_get_active(of->kn))
> return VM_FAULT_SIGBUS;
>
> @@ -374,9 +368,6 @@ static vm_fault_t kernfs_vma_page_mkwrite(struct
> vm_fault *vmf)
> struct kernfs_open_file *of = kernfs_of(file);
> vm_fault_t ret;
>
> - if (!of->vm_ops)
> - return VM_FAULT_SIGBUS;
> -
> if (!kernfs_get_active(of->kn))
> return VM_FAULT_SIGBUS;
>
> @@ -397,9 +388,6 @@ static int kernfs_vma_access(struct
> vm_area_struct *vma, unsigned long addr,
> struct kernfs_open_file *of = kernfs_of(file);
> int ret;
>
> - if (!of->vm_ops)
> - return -EINVAL;
> -
> if (!kernfs_get_active(of->kn))
> return -EINVAL;
>
> @@ -419,9 +407,6 @@ static int kernfs_vma_set_policy(struct
> vm_area_struct *vma,
> struct kernfs_open_file *of = kernfs_of(file);
> int ret;
>
> - if (!of->vm_ops)
> - return 0;
> -
> if (!kernfs_get_active(of->kn))
> return -EINVAL;
>
> @@ -440,9 +425,6 @@ static struct mempolicy
> *kernfs_vma_get_policy(struct vm_area_struct *vma,
> struct kernfs_open_file *of = kernfs_of(file);
> struct mempolicy *pol;
>
> - if (!of->vm_ops)
> - return vma->vm_policy;
> -
> if (!kernfs_get_active(of->kn))
> return vma->vm_policy;
>
> @@ -511,7 +493,7 @@ static int kernfs_fop_mmap(struct file *file,
> struct vm_area_struct *vma)
> * So error if someone is trying to use close.
> */
> rc = -EINVAL;
> - if (vma->vm_ops && vma->vm_ops->close)
> + if (vma->vm_ops->close)
> goto out_put;
>
> rc = 0;
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index e9679016271f..e959623123e4 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -326,7 +326,7 @@ show_map_vma(struct seq_file *m, struct
> vm_area_struct *vma, int is_pid)
> goto done;
> }
>
> - if (vma->vm_ops && vma->vm_ops->name) {
> + if (vma->vm_ops->name) {
> name = vma->vm_ops->name(vma);
> if (name)
> goto done;
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 8f0434a9951a..2e35401a5c68 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7269,7 +7269,7 @@ static void perf_event_mmap_event(struct
> perf_mmap_event *mmap_event)
>
> goto got_name;
> } else {
> - if (vma->vm_ops && vma->vm_ops->name) {
> + if (vma->vm_ops->name) {
> name = (char *) vma->vm_ops->name(vma);
> if (name)
> goto cpy_name;
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 9440d61b925c..e5e7a220a124 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -519,7 +519,7 @@ static __latent_entropy int dup_mmap(struct
> mm_struct *mm,
> if (!(tmp->vm_flags & VM_WIPEONFORK))
> retval = copy_page_range(mm, oldmm, mpnt);
>
> - if (tmp->vm_ops && tmp->vm_ops->open)
> + if (tmp->vm_ops->open)
> tmp->vm_ops->open(tmp);
>
> if (retval)
> diff --git a/mm/gup.c b/mm/gup.c
> index b70d7ba7cc13..b732768ed3ac 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -31,7 +31,7 @@ static struct page *no_page_table(struct
> vm_area_struct *vma,
> * But we can only make this optimization where a hole would
> surely
> * be zero-filled if handle_mm_fault() actually did handle
> it.
> */
> - if ((flags & FOLL_DUMP) && (!vma->vm_ops || !vma->vm_ops-
> >fault))
> + if ((flags & FOLL_DUMP) && !vma->vm_ops->fault)
> return ERR_PTR(-EFAULT);
> return NULL;
> }
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 039ddbc574e9..2065acc5a6aa 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -637,7 +637,7 @@ EXPORT_SYMBOL_GPL(linear_hugepage_index);
> */
> unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
> {
> - if (vma->vm_ops && vma->vm_ops->pagesize)
> + if (vma->vm_ops->pagesize)
> return vma->vm_ops->pagesize(vma);
> return PAGE_SIZE;
> }
> diff --git a/mm/memory.c b/mm/memory.c
> index 7206a634270b..02fbef2bd024 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -768,7 +768,7 @@ static void print_bad_pte(struct vm_area_struct
> *vma, unsigned long addr,
> (void *)addr, vma->vm_flags, vma->anon_vma,
> mapping, index);
> pr_alert("file:%pD fault:%pf mmap:%pf readpage:%pf\n",
> vma->vm_file,
> - vma->vm_ops ? vma->vm_ops->fault : NULL,
> + vma->vm_ops->fault,
> vma->vm_file ? vma->vm_file->f_op->mmap : NULL,
> mapping ? mapping->a_ops->readpage : NULL);
> dump_stack();
> @@ -825,7 +825,7 @@ struct page *_vm_normal_page(struct
> vm_area_struct *vma, unsigned long addr,
> if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) {
> if (likely(!pte_special(pte)))
> goto check_pfn;
> - if (vma->vm_ops && vma->vm_ops->find_special_page)
> + if (vma->vm_ops->find_special_page)
> return vma->vm_ops->find_special_page(vma,
> addr);
> if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
> return NULL;
> @@ -2404,7 +2404,7 @@ static void fault_dirty_shared_page(struct
> vm_area_struct *vma,
> {
> struct address_space *mapping;
> bool dirtied;
> - bool page_mkwrite = vma->vm_ops && vma->vm_ops-
> >page_mkwrite;
> + bool page_mkwrite = vma->vm_ops->page_mkwrite;
>
> dirtied = set_page_dirty(page);
> VM_BUG_ON_PAGE(PageAnon(page), page);
> @@ -2648,7 +2648,7 @@ static int wp_pfn_shared(struct vm_fault *vmf)
> {
> struct vm_area_struct *vma = vmf->vma;
>
> - if (vma->vm_ops && vma->vm_ops->pfn_mkwrite) {
> + if (vma->vm_ops->pfn_mkwrite) {
> int ret;
>
> pte_unmap_unlock(vmf->pte, vmf->ptl);
> @@ -2669,7 +2669,7 @@ static int wp_page_shared(struct vm_fault *vmf)
>
> get_page(vmf->page);
>
> - if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
> + if (vma->vm_ops->page_mkwrite) {
> int tmp;
>
> pte_unmap_unlock(vmf->pte, vmf->ptl);
> @@ -4439,7 +4439,7 @@ int __access_remote_vm(struct task_struct *tsk,
> struct mm_struct *mm,
> vma = find_vma(mm, addr);
> if (!vma || vma->vm_start > addr)
> break;
> - if (vma->vm_ops && vma->vm_ops->access)
> + if (vma->vm_ops->access)
> ret = vma->vm_ops->access(vma, addr,
> buf,
> len,
> write);
> if (ret <= 0)
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 9ac49ef17b4e..f0fcf70bcec7 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -651,13 +651,13 @@ static int vma_replace_policy(struct
> vm_area_struct *vma,
> pr_debug("vma %lx-%lx/%lx vm_ops %p vm_file %p set_policy
> %p\n",
> vma->vm_start, vma->vm_end, vma->vm_pgoff,
> vma->vm_ops, vma->vm_file,
> - vma->vm_ops ? vma->vm_ops->set_policy : NULL);
> + vma->vm_ops->set_policy);
>
> new = mpol_dup(pol);
> if (IS_ERR(new))
> return PTR_ERR(new);
>
> - if (vma->vm_ops && vma->vm_ops->set_policy) {
> + if (vma->vm_ops->set_policy) {
> err = vma->vm_ops->set_policy(vma, new);
> if (err)
> goto err_out;
> @@ -845,7 +845,7 @@ static long do_get_mempolicy(int *policy,
> nodemask_t *nmask,
> up_read(&mm->mmap_sem);
> return -EFAULT;
> }
> - if (vma->vm_ops && vma->vm_ops->get_policy)
> + if (vma->vm_ops->get_policy)
> pol = vma->vm_ops->get_policy(vma, addr);
> else
> pol = vma->vm_policy;
> @@ -1617,7 +1617,7 @@ struct mempolicy *__get_vma_policy(struct
> vm_area_struct *vma,
> struct mempolicy *pol = NULL;
>
> if (vma) {
> - if (vma->vm_ops && vma->vm_ops->get_policy) {
> + if (vma->vm_ops->get_policy) {
> pol = vma->vm_ops->get_policy(vma, addr);
> } else if (vma->vm_policy) {
> pol = vma->vm_policy;
> @@ -1663,7 +1663,7 @@ bool vma_policy_mof(struct vm_area_struct *vma)
> {
> struct mempolicy *pol;
>
> - if (vma->vm_ops && vma->vm_ops->get_policy) {
> + if (vma->vm_ops->get_policy) {
> bool ret = false;
>
> pol = vma->vm_ops->get_policy(vma, vma->vm_start);
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 527c17f31635..5adaf9f9b941 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -177,7 +177,7 @@ static struct vm_area_struct *remove_vma(struct
> vm_area_struct *vma)
> struct vm_area_struct *next = vma->vm_next;
>
> might_sleep();
> - if (vma->vm_ops && vma->vm_ops->close)
> + if (vma->vm_ops->close)
> vma->vm_ops->close(vma);
> if (vma->vm_file)
> fput(vma->vm_file);
> @@ -998,7 +998,7 @@ static inline int is_mergeable_vma(struct
> vm_area_struct *vma,
> return 0;
> if (vma->vm_file != file)
> return 0;
> - if (vma->vm_ops && vma->vm_ops->close)
> + if (vma->vm_ops->close)
> return 0;
> if (!is_mergeable_vm_userfaultfd_ctx(vma,
> vm_userfaultfd_ctx))
> return 0;
> @@ -1638,7 +1638,7 @@ int vma_wants_writenotify(struct vm_area_struct
> *vma, pgprot_t vm_page_prot)
> return 0;
>
> /* The backer wishes to know when pages are first written
> to? */
> - if (vm_ops && (vm_ops->page_mkwrite || vm_ops->pfn_mkwrite))
> + if (vm_ops->page_mkwrite || vm_ops->pfn_mkwrite)
> return 1;
>
> /* The open routine did something to the protections that
> pgprot_modify
> @@ -2624,7 +2624,7 @@ int __split_vma(struct mm_struct *mm, struct
> vm_area_struct *vma,
> struct vm_area_struct *new;
> int err;
>
> - if (vma->vm_ops && vma->vm_ops->split) {
> + if (vma->vm_ops->split) {
> err = vma->vm_ops->split(vma, addr);
> if (err)
> return err;
> @@ -2657,7 +2657,7 @@ int __split_vma(struct mm_struct *mm, struct
> vm_area_struct *vma,
> if (new->vm_file)
> get_file(new->vm_file);
>
> - if (new->vm_ops && new->vm_ops->open)
> + if (new->vm_ops->open)
> new->vm_ops->open(new);
>
> if (new_below)
> @@ -2671,7 +2671,7 @@ int __split_vma(struct mm_struct *mm, struct
> vm_area_struct *vma,
> return 0;
>
> /* Clean everything up if vma_adjust failed. */
> - if (new->vm_ops && new->vm_ops->close)
> + if (new->vm_ops->close)
> new->vm_ops->close(new);
> if (new->vm_file)
> fput(new->vm_file);
> @@ -3232,7 +3232,7 @@ struct vm_area_struct *copy_vma(struct
> vm_area_struct **vmap,
> goto out_free_mempol;
> if (new_vma->vm_file)
> get_file(new_vma->vm_file);
> - if (new_vma->vm_ops && new_vma->vm_ops->open)
> + if (new_vma->vm_ops->open)
> new_vma->vm_ops->open(new_vma);
> vma_link(mm, new_vma, prev, rb_link, rb_parent);
> *need_rmap_locks = false;
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 5c2e18505f75..7ab222c283de 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -302,7 +302,7 @@ static unsigned long move_vma(struct
> vm_area_struct *vma,
> need_rmap_locks);
> if (moved_len < old_len) {
> err = -ENOMEM;
> - } else if (vma->vm_ops && vma->vm_ops->mremap) {
> + } else if (vma->vm_ops->mremap) {
> err = vma->vm_ops->mremap(new_vma);
> }
>
> diff --git a/mm/nommu.c b/mm/nommu.c
> index f00f209833ab..73f66e81cfb0 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -764,7 +764,7 @@ static void delete_vma_from_mm(struct
> vm_area_struct *vma)
> */
> static void delete_vma(struct mm_struct *mm, struct vm_area_struct
> *vma)
> {
> - if (vma->vm_ops && vma->vm_ops->close)
> + if (vma->vm_ops->close)
> vma->vm_ops->close(vma);
> if (vma->vm_file)
> fput(vma->vm_file);
> @@ -1496,7 +1496,7 @@ int split_vma(struct mm_struct *mm, struct
> vm_area_struct *vma,
> region->vm_pgoff = new->vm_pgoff += npages;
> }
>
> - if (new->vm_ops && new->vm_ops->open)
> + if (new->vm_ops->open)
> new->vm_ops->open(new);
>
> delete_vma_from_mm(vma);

Today's -next on Apalis T30 [1] gives the following error upon boot:

[ 16.147496] Unable to handle kernel NULL pointer dereference at
virtual address 0000002c
[ 16.156152] pgd = 843045af
[ 16.158986] [0000002c] *pgd=facd9831
[ 16.162578] Internal error: Oops: 17 [#1] PREEMPT SMP ARM
[ 16.167970] Modules linked in:
[ 16.171034] CPU: 2 PID: 442 Comm: polkitd Not tainted 4.18.0-rc5-
next-20180716-dirty #75
[ 16.179111] Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
[ 16.185382] PC is at show_map_vma.constprop.3+0xac/0x158
[ 16.190686] LR is at show_map_vma.constprop.3+0xa8/0x158
[ 16.195989] pc : [<c02c4900>] lr : [<c02c48fc>] psr: 800e0013
[ 16.202243] sp : ec02de60 ip : 000003ce fp : c0f09a3c
[ 16.207457] r10: ec02df78 r9 : 00000000 r8 : 00000000
[ 16.212672] r7 : 00000000 r6 : eda8ec48 r5 : 00000000 r4 :
c0f09a3c
[ 16.219188] r3 : 00000000 r2 : ed1df000 r1 : 00000020 r0 :
eda8ec48
[ 16.225705] Flags: Nzcv IRQs on FIQs on Mode SVC_32 ISA
ARM Segment none
[ 16.232829] Control: 10c5387d Table: ac01804a DAC: 00000051
[ 16.238573] Process polkitd (pid: 442, stack limit = 0xc0e83ce5)
[ 16.244572] Stack: (0xec02de60 to 0xec02e000)
[ 16.248928] de60: 00000000 00000000 00000000 00000000 eda8ec48
eda8ec48 c0f09a3c 000003a6
[ 16.257097] de80: ecf46300 00000096 00000000 c02c4efc eda8ec48
00000000 000003a6 c0289908
[ 16.265287] dea0: 0000000c eda8ec78 ecf46300 000003f4 00081114
eda8ec60 00000000 c0f04c48
[ 16.273482] dec0: c028956c 00000400 ec02df78 00000000 00081108
00000400 00000000 c0263b20
[ 16.281671] dee0: 5b4c9a7c 0ee6b280 000039ea 00000000 c0f04c48
8bb3ec56 c0f04c48 be8c7a00
[ 16.289853] df00: ecf46308 00000000 000007ff c0f04c48 00000001
00000000 00000000 00000000
[ 16.298037] df20: 00000000 8bb3ec56 000039ea 8bb3ec56 ecf46300
00081108 00000400 ec02df78
[ 16.306210] df40: 00000000 00081108 00000400 c0263cdc c0f04c48
b686ac78 000005e8 c0f04c48
[ 16.314381] df60: ecf46303 00002400 00000000 ecf46300 00081108
c02641c0 00002400 00000000
[ 16.322549] df80: 00000000 8bb3ec56 00022698 b686ac78 000005e8
00000003 c0101204 ec02c000
[ 16.330718] dfa0: 00000003 c0101000 00022698 b686ac78 00000009
00081108 00000400 000000c2
[ 16.338886] dfc0: 00022698 b686ac78 000005e8 00000003 0000004b
be8c7af4 00000000 00000000
[ 16.347053] dfe0: 0004d1b2 be8c7a84 b686b94c b686ac98 000e0010
00000009 00000000 00000000
[ 16.355237] [<c02c4900>] (show_map_vma.constprop.3) from
[<c02c4efc>] (show_pid_map+0x10/0x34)
[ 16.363846] [<c02c4efc>] (show_pid_map) from [<c0289908>]
(seq_read+0x39c/0x4f4)
[ 16.371264] [<c0289908>] (seq_read) from [<c0263b20>]
(__vfs_read+0x2c/0x15c)
[ 16.378401] [<c0263b20>] (__vfs_read) from [<c0263cdc>]
(vfs_read+0x8c/0x110)
[ 16.385546] [<c0263cdc>] (vfs_read) from [<c02641c0>]
(ksys_read+0x4c/0xac)
[ 16.392519] [<c02641c0>] (ksys_read) from [<c0101000>]
(ret_fast_syscall+0x0/0x54)
[ 16.400083] Exception stack(0xec02dfa8 to 0xec02dff0)
[ 16.405135] dfa0: 00022698 b686ac78 00000009
00081108 00000400 000000c2
[ 16.413311] dfc0: 00022698 b686ac78 000005e8 00000003 0000004b
be8c7af4 00000000 00000000
[ 16.421485] dfe0: 0004d1b2 be8c7a84 b686b94c b686ac98
[ 16.426542] Code: e1cd80f0 e5947020 ebfffb4f e5943048 (e593302c)
[ 16.432734] ---[ end trace 5dbf91c64da6bd91 ]---

Reverting this makes it behave as expected again. Anybody knows what is
going on?

[1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
/tree/arch/arm/boot/dts/tegra30-apalis-eval.dts?h=next-20180716
--
Best regards - Mit freundlichen GrÃssen - Meilleures salutations

Marcel Ziswiler
Platform Manager Embedded Linux

Toradex AG
Altsagenstrasse 5 | 6048 Horw/Luzern | Switzerland | T: +41 41 500 48 00
(main line) | Direct: +41 41 500 48 10

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