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

From: Dmitry Osipenko
Date: Thu Jul 28 2022 - 12:57:16 EST

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In reply to: Liam Howlett: "Re: [PATCH v12 22/69] mm/mmap: change do_brk_flags() to expand existing VMA and add do_brk_munmap()"
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28.07.2022 03:57, Liam Howlett пишет:
> * Dmitry Osipenko <digetx@xxxxxxxxx> [220725 15:14]:
>> 25.07.2022 21:49, Liam Howlett пишет:
>>> * Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> [220725 10:00]:
>>>> * Dmitry Osipenko <digetx@xxxxxxxxx> [220723 11:01]:
>>>>> 20.07.2022 05:17, Liam Howlett пишет:
>>>>>> From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
>>>>>>
>>>>>> 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@xxxxxxxxxx
>>>>>> Link: https://lkml.kernel.org/r/20220621204632.3370049-23-Liam.Howlett@xxxxxxxxxx
>>>>>> Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
>>>>>> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
>>>>>> Cc: David Howells <dhowells@xxxxxxxxxx>
>>>>>> Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
>>>>>> Cc: SeongJae Park <sj@xxxxxxxxxx>
>>>>>> Cc: Vlastimil Babka <vbabka@xxxxxxx>
>>>>>> Cc: Will Deacon <will@xxxxxxxxxx>
>>>>>> Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
>>>>>> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>>>>>> ---
>>>>>> 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@xxxxxxxxxx/
>>>> 2. https://lore.kernel.org/linux-mm/20220721005828.379405-1-Liam.Howlett@xxxxxxxxxx/
>>>> 3. https://lore.kernel.org/linux-mm/20220721005237.377987-1-Liam.Howlett@xxxxxxxxxx/
>>>>
>>>
>>> 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.
>
> Thanks. I don't have an NVIDIA Tegra tablet to test, but I did manage
> to find an issue with my 32b allocator. I was also able to get plasma
> running painfully slow in qemu armv7l with 1GB of ram. Unfortunately
> the maple tree has been dropped from linux-next for this merge window.
> I'll CC you on the allocator fix when I send it out to the linux-mm list
> and I will keep trying to replicate this exact crash.

Thank you for update! I'll be happy to try the fixed version, feel free
to CC me. I may also try to check if this problem reproducible in qemu
over this weekend.

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