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Message-ID: <f5e99dbb-7008-dcf8-3e85-2f161056b37a@gmail.com>
Date: Sat, 23 Jul 2022 18:01:09 +0300
From: Dmitry Osipenko <digetx@...il.com>
To: Liam Howlett <liam.howlett@...cle.com>,
"maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Hugh Dickins <hughd@...gle.com>
Cc: Yu Zhao <yuzhao@...gle.com>
Subject: Re: [PATCH v12 22/69] mm/mmap: change do_brk_flags() to expand
existing VMA and add do_brk_munmap()
20.07.2022 05:17, Liam Howlett пишет:
> From: "Liam R. Howlett" <Liam.Howlett@...cle.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@...cle.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: David Howells <dhowells@...hat.com>
> Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> Cc: SeongJae Park <sj@...nel.org>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Will Deacon <will@...nel.org>
> Cc: Davidlohr Bueso <dave@...olabs.net>
> Signed-off-by: Andrew Morton <akpm@...ux-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
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