Re: [PATCH v12 22/69] mm/mmap: change do_brk_flags() to expand existing VMA and add do_brk_munmap()

Liam Howlett
2022-07-25T14:01:44Z

* Dmitry Osipenko <digetx@gmail.com> [220723 11:01]:
> 20.07.2022 05:17, Liam Howlett пишет:
> > From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
> >
> > Avoid allocating a new VMA when it a vma modification can occur. When a
> > brk() can expand or contract a VMA, then the single store operation will
> > only modify one index of the maple tree instead of causing a node to split
> > or coalesce. This avoids unnecessary allocations/frees of maple tree
> > nodes and VMAs.
> >
> > Move some limit & flag verifications out of the do_brk_flags() function to
> > use only relevant checks in the code path of bkr() and vm_brk_flags().
> >
> > Set the vma to check if it can expand in vm_brk_flags() if extra criteria
> > are met.
> >
> > Drop userfaultfd from do_brk_flags() path and only use it in
> > vm_brk_flags() path since that is the only place a munmap will happen.
> >
> > Add a wraper for munmap for the brk case called do_brk_munmap().
> >
> > Link: https://lkml.kernel.org/r/20220504011345.662299-7-Liam.Howlett@oracle.com
> > Link: https://lkml.kernel.org/r/20220621204632.3370049-23-Liam.Howlett@oracle.com
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: David Howells <dhowells@redhat.com>
> > Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> > Cc: SeongJae Park <sj@kernel.org>
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Davidlohr Bueso <dave@stgolabs.net>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > ---
> > mm/mmap.c | 239 ++++++++++++++++++++++++++++++++++++++++--------------
> > 1 file changed, 179 insertions(+), 60 deletions(-)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 02d2fd90af80..33b408653201 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -194,17 +194,40 @@ static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
> > return next;
> > }
> >
> > -static int do_brk_flags(unsigned long addr, unsigned long request, unsigned long flags,
> > - struct list_head *uf);
> > +/*
> > + * check_brk_limits() - Use platform specific check of range & verify mlock
> > + * limits.
> > + * @addr: The address to check
> > + * @len: The size of increase.
> > + *
> > + * Return: 0 on success.
> > + */
> > +static int check_brk_limits(unsigned long addr, unsigned long len)
> > +{
> > + unsigned long mapped_addr;
> > +
> > + mapped_addr = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
> > + if (IS_ERR_VALUE(mapped_addr))
> > + return mapped_addr;
> > +
> > + return mlock_future_check(current->mm, current->mm->def_flags, len);
> > +}
> > +static int do_brk_munmap(struct ma_state *mas, struct vm_area_struct *vma,
> > + unsigned long newbrk, unsigned long oldbrk,
> > + struct list_head *uf);
> > +static int do_brk_flags(struct ma_state *mas, struct vm_area_struct *brkvma,
> > + unsigned long addr, unsigned long request,
> > + unsigned long flags);
> > SYSCALL_DEFINE1(brk, unsigned long, brk)
> > {
> > unsigned long newbrk, oldbrk, origbrk;
> > struct mm_struct *mm = current->mm;
> > - struct vm_area_struct *next;
> > + struct vm_area_struct *brkvma, *next = NULL;
> > unsigned long min_brk;
> > bool populate;
> > bool downgraded = false;
> > LIST_HEAD(uf);
> > + MA_STATE(mas, &mm->mm_mt, 0, 0);
> >
> > if (mmap_write_lock_killable(mm))
> > return -EINTR;
> > @@ -246,35 +269,52 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
> >
> > /*
> > * Always allow shrinking brk.
> > - * __do_munmap() may downgrade mmap_lock to read.
> > + * do_brk_munmap() may downgrade mmap_lock to read.
> > */
> > if (brk <= mm->brk) {
> > int ret;
> >
> > + /* Search one past newbrk */
> > + mas_set(&mas, newbrk);
> > + brkvma = mas_find(&mas, oldbrk);
> > + BUG_ON(brkvma == NULL);
> > + if (brkvma->vm_start >= oldbrk)
> > + goto out; /* mapping intersects with an existing non-brk vma. */
> > /*
> > - * mm->brk must to be protected by write mmap_lock so update it
> > - * before downgrading mmap_lock. When __do_munmap() fails,
> > - * mm->brk will be restored from origbrk.
> > + * mm->brk must be protected by write mmap_lock.
> > + * do_brk_munmap() may downgrade the lock, so update it
> > + * before calling do_brk_munmap().
> > */
> > mm->brk = brk;
> > - ret = __do_munmap(mm, newbrk, oldbrk-newbrk, &uf, true);
> > - if (ret < 0) {
> > - mm->brk = origbrk;
> > - goto out;
> > - } else if (ret == 1) {
> > + mas.last = oldbrk - 1;
> > + ret = do_brk_munmap(&mas, brkvma, newbrk, oldbrk, &uf);
> > + if (ret == 1) {
> > downgraded = true;
> > - }
> > - goto success;
> > + goto success;
> > + } else if (!ret)
> > + goto success;
> > +
> > + mm->brk = origbrk;
> > + goto out;
> > }
> >
> > - /* Check against existing mmap mappings. */
> > - next = find_vma(mm, oldbrk);
> > + if (check_brk_limits(oldbrk, newbrk - oldbrk))
> > + goto out;
> > +
> > + /*
> > + * Only check if the next VMA is within the stack_guard_gap of the
> > + * expansion area
> > + */
> > + mas_set(&mas, oldbrk);
> > + next = mas_find(&mas, newbrk - 1 + PAGE_SIZE + stack_guard_gap);
> > if (next && newbrk + PAGE_SIZE > vm_start_gap(next))
> > goto out;
> >
> > + brkvma = mas_prev(&mas, mm->start_brk);
> > /* Ok, looks good - let it rip. */
> > - if (do_brk_flags(oldbrk, newbrk-oldbrk, 0, &uf) < 0)
> > + if (do_brk_flags(&mas, brkvma, oldbrk, newbrk - oldbrk, 0) < 0)
> > goto out;
> > +
> > mm->brk = brk;
> >
> > success:
> > @@ -2805,38 +2845,55 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
> > }
> >
> > /*
> > - * this is really a simplified "do_mmap". it only handles
> > - * anonymous maps. eventually we may be able to do some
> > - * brk-specific accounting here.
> > + * brk_munmap() - Unmap a parital vma.
> > + * @mas: The maple tree state.
> > + * @vma: The vma to be modified
> > + * @newbrk: the start of the address to unmap
> > + * @oldbrk: The end of the address to unmap
> > + * @uf: The userfaultfd list_head
> > + *
> > + * Returns: 1 on success.
> > + * unmaps a partial VMA mapping. Does not handle alignment, downgrades lock if
> > + * possible.
> > */
> > -static int do_brk_flags(unsigned long addr, unsigned long len,
> > - unsigned long flags, struct list_head *uf)
> > +static int do_brk_munmap(struct ma_state *mas, struct vm_area_struct *vma,
> > + unsigned long newbrk, unsigned long oldbrk,
> > + struct list_head *uf)
> > {
> > - struct mm_struct *mm = current->mm;
> > - struct vm_area_struct *vma, *prev;
> > - pgoff_t pgoff = addr >> PAGE_SHIFT;
> > - int error;
> > - unsigned long mapped_addr;
> > - validate_mm_mt(mm);
> > -
> > - /* Until we need other flags, refuse anything except VM_EXEC. */
> > - if ((flags & (~VM_EXEC)) != 0)
> > - return -EINVAL;
> > - flags |= VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
> > -
> > - mapped_addr = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
> > - if (IS_ERR_VALUE(mapped_addr))
> > - return mapped_addr;
> > + struct mm_struct *mm = vma->vm_mm;
> > + int ret;
> >
> > - error = mlock_future_check(mm, mm->def_flags, len);
> > - if (error)
> > - return error;
> > + arch_unmap(mm, newbrk, oldbrk);
> > + ret = __do_munmap(mm, newbrk, oldbrk - newbrk, uf, true);
> > + validate_mm_mt(mm);
> > + return ret;
> > +}
> >
> > - /* Clear old maps, set up prev and uf */
> > - if (munmap_vma_range(mm, addr, len, &prev, uf))
> > - return -ENOMEM;
> > +/*
> > + * do_brk_flags() - Increase the brk vma if the flags match.
> > + * @mas: The maple tree state.
> > + * @addr: The start address
> > + * @len: The length of the increase
> > + * @vma: The vma,
> > + * @flags: The VMA Flags
> > + *
> > + * Extend the brk VMA from addr to addr + len. If the VMA is NULL or the flags
> > + * do not match then create a new anonymous VMA. Eventually we may be able to
> > + * do some brk-specific accounting here.
> > + */
> > +static int do_brk_flags(struct ma_state *mas, struct vm_area_struct *vma,
> > + unsigned long addr, unsigned long len,
> > + unsigned long flags)
> > +{
> > + struct mm_struct *mm = current->mm;
> > + struct vm_area_struct *prev = NULL;
> >
> > - /* Check against address space limits *after* clearing old maps... */
> > + validate_mm_mt(mm);
> > + /*
> > + * Check against address space limits by the changed size
> > + * Note: This happens *after* clearing old mappings in some code paths.
> > + */
> > + flags |= VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
> > if (!may_expand_vm(mm, flags, len >> PAGE_SHIFT))
> > return -ENOMEM;
> >
> > @@ -2846,30 +2903,56 @@ static int do_brk_flags(unsigned long addr, unsigned long len,
> > if (security_vm_enough_memory_mm(mm, len >> PAGE_SHIFT))
> > return -ENOMEM;
> >
> > - /* Can we just expand an old private anonymous mapping? */
> > - vma = vma_merge(mm, prev, addr, addr + len, flags,
> > - NULL, NULL, pgoff, NULL, NULL_VM_UFFD_CTX, NULL);
> > - if (vma)
> > - goto out;
> > -
> > /*
> > - * create a vma struct for an anonymous mapping
> > + * Expand the existing vma if possible; Note that singular lists do not
> > + * occur after forking, so the expand will only happen on new VMAs.
> > */
> > - vma = vm_area_alloc(mm);
> > - if (!vma) {
> > - vm_unacct_memory(len >> PAGE_SHIFT);
> > - return -ENOMEM;
> > + if (vma &&
> > + (!vma->anon_vma || list_is_singular(&vma->anon_vma_chain)) &&
> > + ((vma->vm_flags & ~VM_SOFTDIRTY) == flags)) {
> > + mas->index = vma->vm_start;
> > + mas->last = addr + len - 1;
> > + vma_adjust_trans_huge(vma, addr, addr + len, 0);
> > + if (vma->anon_vma) {
> > + anon_vma_lock_write(vma->anon_vma);
> > + anon_vma_interval_tree_pre_update_vma(vma);
> > + }
> > + vma->vm_end = addr + len;
> > + vma->vm_flags |= VM_SOFTDIRTY;
> > + if (mas_store_gfp(mas, vma, GFP_KERNEL))
> > + goto mas_expand_failed;
> > +
> > + if (vma->anon_vma) {
> > + anon_vma_interval_tree_post_update_vma(vma);
> > + anon_vma_unlock_write(vma->anon_vma);
> > + }
> > + khugepaged_enter_vma(vma, flags);
> > + goto out;
> > }
> > + prev = vma;
> > +
> > + /* create a vma struct for an anonymous mapping */
> > + vma = vm_area_alloc(mm);
> > + if (!vma)
> > + goto vma_alloc_fail;
> >
> > vma_set_anonymous(vma);
> > vma->vm_start = addr;
> > vma->vm_end = addr + len;
> > - vma->vm_pgoff = pgoff;
> > + vma->vm_pgoff = addr >> PAGE_SHIFT;
> > vma->vm_flags = flags;
> > vma->vm_page_prot = vm_get_page_prot(flags);
> > - if (vma_link(mm, vma, prev))
> > - goto no_vma_link;
> > + mas_set_range(mas, vma->vm_start, addr + len - 1);
> > + if (mas_store_gfp(mas, vma, GFP_KERNEL))
> > + goto mas_store_fail;
> >
> > + mm->map_count++;
> > +
> > + if (!prev)
> > + prev = mas_prev(mas, 0);
> > +
> > + __vma_link_list(mm, vma, prev);
> > + mm->map_count++;
> > out:
> > perf_event_mmap(vma);
> > mm->total_vm += len >> PAGE_SHIFT;
> > @@ -2880,18 +2963,29 @@ static int do_brk_flags(unsigned long addr, unsigned long len,
> > validate_mm_mt(mm);
> > return 0;
> >
> > -no_vma_link:
> > +mas_store_fail:
> > vm_area_free(vma);
> > +vma_alloc_fail:
> > + vm_unacct_memory(len >> PAGE_SHIFT);
> > + return -ENOMEM;
> > +
> > +mas_expand_failed:
> > + if (vma->anon_vma) {
> > + anon_vma_interval_tree_post_update_vma(vma);
> > + anon_vma_unlock_write(vma->anon_vma);
> > + }
> > return -ENOMEM;
> > }
> >
> > int vm_brk_flags(unsigned long addr, unsigned long request, unsigned long flags)
> > {
> > struct mm_struct *mm = current->mm;
> > + struct vm_area_struct *vma = NULL;
> > unsigned long len;
> > int ret;
> > bool populate;
> > LIST_HEAD(uf);
> > + MA_STATE(mas, &mm->mm_mt, addr, addr);
> >
> > len = PAGE_ALIGN(request);
> > if (len < request)
> > @@ -2902,13 +2996,38 @@ int vm_brk_flags(unsigned long addr, unsigned long request, unsigned long flags)
> > if (mmap_write_lock_killable(mm))
> > return -EINTR;
> >
> > - ret = do_brk_flags(addr, len, flags, &uf);
> > + /* Until we need other flags, refuse anything except VM_EXEC. */
> > + if ((flags & (~VM_EXEC)) != 0)
> > + return -EINVAL;
> > +
> > + ret = check_brk_limits(addr, len);
> > + if (ret)
> > + goto limits_failed;
> > +
> > + if (find_vma_intersection(mm, addr, addr + len))
> > + ret = do_munmap(mm, addr, len, &uf);
> > +
> > + if (ret)
> > + goto munmap_failed;
> > +
> > + vma = mas_prev(&mas, 0);
> > + if (!vma || vma->vm_end != addr || vma_policy(vma) ||
> > + !can_vma_merge_after(vma, flags, NULL, NULL,
> > + addr >> PAGE_SHIFT, NULL_VM_UFFD_CTX, NULL))
> > + vma = NULL;
> > +
> > + ret = do_brk_flags(&mas, vma, addr, len, flags);
> > populate = ((mm->def_flags & VM_LOCKED) != 0);
> > mmap_write_unlock(mm);
> > userfaultfd_unmap_complete(mm, &uf);
> > if (populate && !ret)
> > mm_populate(addr, len);
> > return ret;
> > +
> > +munmap_failed:
> > +limits_failed:
> > + mmap_write_unlock(mm);
> > + return ret;
> > }
> > EXPORT_SYMBOL(vm_brk_flags);
> >
>
> Hello,
>
> I cannot complete booting into graphics environment on ARM32 because
> do_brk_flags() now crashes with a BUG_ON() on a recent linux-next and
> this patch should be the cause. Please take a look, thanks in advance.
>
> ------------[ cut here ]------------
> kernel BUG at lib/maple_tree.c:911!
> Internal error: Oops - BUG: 0 [#1] SMP ARM
> Modules linked in:
> CPU: 1 PID: 692 Comm: kwin_x11 Not tainted
> 5.19.0-rc7-next-20220722-00130-g1583ab12487b #21
> Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
> PC is at mas_update_gap+0xac/0x1a8
> LR is at 0xcc343e00
> pc : [<c0747314>] lr : [<cc343e00>] psr: 60080013
> sp : f1299ac8 ip : 999b6000 fp : f1299ae4
> r10: c1062588 r9 : 00000023 r8 : 00000001
> r7 : 0000001f r6 : cc0ea6a8 r5 : 00000000 r4 : f1299f54
> r3 : 00000000 r2 : c25a2000 r1 : 999b6000 r0 : 00000000
> Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
> Control: 10c5387d Table: 0d28404a DAC: 00000051
> Register r0 information: NULL pointer
> Register r1 information: non-paged memory
> Register r2 information: slab mm_struct start c25a2000 pointer offset 0
> size 168
> Register r3 information: NULL pointer
> Register r4 information: 2-page vmalloc region starting at 0xf1298000
> allocated at kernel_clone+0x64/0x43c
> Register r5 information: NULL pointer
> Register r6 information: slab maple_node start cc0ea600 pointer offset 168
> Register r7 information: non-paged memory
> Register r8 information: non-paged memory
> Register r9 information: non-paged memory
> Register r10 information: non-slab/vmalloc memory
> Register r11 information: 2-page vmalloc region starting at 0xf1298000
> allocated at kernel_clone+0x64/0x43c
> Register r12 information: non-paged memory
> Process kwin_x11 (pid: 692, stack limit = 0x976e11bf)
> ...
> Backtrace:
> mas_update_gap from mas_wr_modify+0x1b4/0x1898
> r7:0000001f r6:00000000 r5:f1299e90 r4:f1299f54
> mas_wr_modify from mas_wr_store_entry+0x138/0x4d8
> r10:cd26febc r9:00000023 r8:f1299f54 r7:00000cc0 r6:cd21d600 r5:f1299f54
> r4:f1299e90
> mas_wr_store_entry from mas_store_gfp+0x64/0x154
> r9:00000023 r8:f1299f54 r7:00000cc0 r6:cd21d600 r5:cd26fea0 r4:f1299f54
> mas_store_gfp from do_brk_flags+0x21c/0x318
> r10:cd26febc r9:00000023 r8:f1299f54 r7:0097a000 r6:cd26fec4 r5:c25a2000
> r4:cd26fea0
> do_brk_flags from sys_brk+0x27c/0x3c8
> r10:c25a2038 r9:00957000 r8:00000000 r7:cd21d600 r6:0097a000 r5:00957000
> r4:c25a2000
> sys_brk from ret_fast_syscall+0x0/0x1c

Thanks for the report. I'm trying to test this now in qemu. I have a
few extra patches that have been sent to the linux-mm but have not made
it into next as of today (next-20220725) [1] [2] [3]. I don't think
they will make a difference but you can try them while I keep working on
testing arm32 on this end.

1. https://lore.kernel.org/linux-mm/20220722160546.1478722-1-Liam.Howlett@oracle.com/
2. https://lore.kernel.org/linux-mm/20220721005828.379405-1-Liam.Howlett@oracle.com/
3. https://lore.kernel.org/linux-mm/20220721005237.377987-1-Liam.Howlett@oracle.com/

Regards,
Liam