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

[Dmitry Osipenko <digetx@gmail.com>]

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