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

Dmitry Osipenko
2022-07-25T19:14:18Z

25.07.2022 21:49, Liam Howlett пишет:
> * Liam R. Howlett <Liam.Howlett@Oracle.com> [220725 10:00]:
>> * 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/
>>
>
> Dmitry,
>
> I am having a hard time reproducing this issue. What linux-next tag are
> you using?

The next-20220722, like my trace log says. It has been broken for about
2+ weeks in -next. For me the bug is triggered by loading KDE plasma on
NVIDIA Tegra tablet. I may try to reproduce it in Qemu if time will allow.