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Date: Fri, 9 Oct 2020 09:16:49 +0200
From: Christian König <ckoenig.leichtzumerken@...il.com>
To: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
linaro-mm-sig@...ts.linaro.org, dri-devel@...ts.freedesktop.org,
linux-media@...r.kernel.org, chris@...is-wilson.co.uk,
airlied@...hat.com, akpm@...ux-foundation.org,
sumit.semwal@...aro.org
Subject: Re: [PATCH 1/4] mm: introduce vma_set_file function v2
Am 08.10.20 um 16:12 schrieb Daniel Vetter:
> On Thu, Oct 08, 2020 at 01:23:39PM +0200, Christian König wrote:
>> Add the new vma_set_file() function to allow changing
>> vma->vm_file with the necessary refcount dance.
>>
>> v2: add more users of this.
>>
>> Signed-off-by: Christian König <christian.koenig@....com>
>> ---
>> drivers/dma-buf/dma-buf.c | 16 +++++-----------
>> drivers/gpu/drm/etnaviv/etnaviv_gem.c | 4 +---
>> drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 3 +--
>> drivers/gpu/drm/i915/gem/i915_gem_mman.c | 4 ++--
>> drivers/gpu/drm/msm/msm_gem.c | 4 +---
>> drivers/gpu/drm/omapdrm/omap_gem.c | 3 +--
>> drivers/gpu/drm/vgem/vgem_drv.c | 3 +--
>> drivers/staging/android/ashmem.c | 5 ++---
>> include/linux/mm.h | 2 ++
>> mm/mmap.c | 16 ++++++++++++++++
>> 10 files changed, 32 insertions(+), 28 deletions(-)
>>
>> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
>> index a6ba4d598f0e..e4316aa7e0f4 100644
>> --- a/drivers/dma-buf/dma-buf.c
>> +++ b/drivers/dma-buf/dma-buf.c
>> @@ -1163,20 +1163,14 @@ int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
>> return -EINVAL;
>>
>> /* readjust the vma */
>> - get_file(dmabuf->file);
>> - oldfile = vma->vm_file;
>> - vma->vm_file = dmabuf->file;
>> + oldfile = vma_set_file(vma, dmabuf->file);
>> vma->vm_pgoff = pgoff;
>>
>> ret = dmabuf->ops->mmap(dmabuf, vma);
>> - if (ret) {
>> - /* restore old parameters on failure */
>> - vma->vm_file = oldfile;
>> - fput(dmabuf->file);
>> - } else {
>> - if (oldfile)
>> - fput(oldfile);
>> - }
>> + /* restore old parameters on failure */
>> + if (ret)
>> + vma_set_file(vma, oldfile);
> I think these two lines here are cargo-cult: If this fails, the mmap fails
> and therefore the vma structure is kfreed. No point at all in restoring
> anything.
This was explicitly added with this patch to fix a problem:
commit 495c10cc1c0c359871d5bef32dd173252fc17995
Author: John Sheu <sheu@...gle.com>
Date: Mon Feb 11 17:50:24 2013 -0800
CHROMIUM: dma-buf: restore args on failure of dma_buf_mmap
Callers to dma_buf_mmap expect to fput() the vma struct's vm_file
themselves on failure. Not restoring the struct's data on failure
causes a double-decrement of the vm_file's refcount.
> With that: Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
Can I keep that even with the error handling working? :)
Christian.
>
>> +
>> return ret;
>>
>> }
>> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
>> index 312e9d58d5a7..10ce267c0947 100644
>> --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
>> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
>> @@ -145,10 +145,8 @@ static int etnaviv_gem_mmap_obj(struct etnaviv_gem_object *etnaviv_obj,
>> * address_space (so unmap_mapping_range does what we want,
>> * in particular in the case of mmap'd dmabufs)
>> */
>> - fput(vma->vm_file);
>> - get_file(etnaviv_obj->base.filp);
>> vma->vm_pgoff = 0;
>> - vma->vm_file = etnaviv_obj->base.filp;
>> + vma_set_file(vma, etnaviv_obj->base.filp);
>>
>> vma->vm_page_prot = vm_page_prot;
>> }
>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>> index fec0e1e3dc3e..8ce4c9e28b87 100644
>> --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>> @@ -119,8 +119,7 @@ static int i915_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *
>> if (ret)
>> return ret;
>>
>> - fput(vma->vm_file);
>> - vma->vm_file = get_file(obj->base.filp);
>> + vma_set_file(vma, obj->base.filp);
>>
>> return 0;
>> }
>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
>> index 3d69e51f3e4d..c9d5f1a38af3 100644
>> --- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
>> @@ -893,8 +893,8 @@ int i915_gem_mmap(struct file *filp, struct vm_area_struct *vma)
>> * requires avoiding extraneous references to their filp, hence why
>> * we prefer to use an anonymous file for their mmaps.
>> */
>> - fput(vma->vm_file);
>> - vma->vm_file = anon;
>> + vma_set_file(vma, anon);
>> + fput(anon);
>>
>> switch (mmo->mmap_type) {
>> case I915_MMAP_TYPE_WC:
>> diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
>> index de915ff6f4b4..a71f42870d5e 100644
>> --- a/drivers/gpu/drm/msm/msm_gem.c
>> +++ b/drivers/gpu/drm/msm/msm_gem.c
>> @@ -223,10 +223,8 @@ int msm_gem_mmap_obj(struct drm_gem_object *obj,
>> * address_space (so unmap_mapping_range does what we want,
>> * in particular in the case of mmap'd dmabufs)
>> */
>> - fput(vma->vm_file);
>> - get_file(obj->filp);
>> vma->vm_pgoff = 0;
>> - vma->vm_file = obj->filp;
>> + vma_set_file(vma, obj->filp);
>>
>> vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
>> }
>> diff --git a/drivers/gpu/drm/omapdrm/omap_gem.c b/drivers/gpu/drm/omapdrm/omap_gem.c
>> index 979d53a93c2b..0d4542ff1d7d 100644
>> --- a/drivers/gpu/drm/omapdrm/omap_gem.c
>> +++ b/drivers/gpu/drm/omapdrm/omap_gem.c
>> @@ -564,9 +564,8 @@ int omap_gem_mmap_obj(struct drm_gem_object *obj,
>> * address_space (so unmap_mapping_range does what we want,
>> * in particular in the case of mmap'd dmabufs)
>> */
>> - fput(vma->vm_file);
>> vma->vm_pgoff = 0;
>> - vma->vm_file = get_file(obj->filp);
>> + vma_set_file(vma, obj->filp);
>>
>> vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
>> }
>> diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
>> index fa54a6d1403d..ea0eecae5153 100644
>> --- a/drivers/gpu/drm/vgem/vgem_drv.c
>> +++ b/drivers/gpu/drm/vgem/vgem_drv.c
>> @@ -397,8 +397,7 @@ static int vgem_prime_mmap(struct drm_gem_object *obj,
>> if (ret)
>> return ret;
>>
>> - fput(vma->vm_file);
>> - vma->vm_file = get_file(obj->filp);
>> + vma_set_file(vma, obj->filp);
>> vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
>> vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
>>
>> diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
>> index 10b4be1f3e78..a51dc089896e 100644
>> --- a/drivers/staging/android/ashmem.c
>> +++ b/drivers/staging/android/ashmem.c
>> @@ -450,9 +450,8 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
>> vma_set_anonymous(vma);
>> }
>>
>> - if (vma->vm_file)
>> - fput(vma->vm_file);
>> - vma->vm_file = asma->file;
>> + vma_set_file(vma, asma->file);
>> + fput(asma->file);
>>
>> out:
>> mutex_unlock(&ashmem_mutex);
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index ca6e6a81576b..a558602afe1b 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2693,6 +2693,8 @@ static inline void vma_set_page_prot(struct vm_area_struct *vma)
>> }
>> #endif
>>
>> +struct file *vma_set_file(struct vm_area_struct *vma, struct file *file);
>> +
>> #ifdef CONFIG_NUMA_BALANCING
>> unsigned long change_prot_numa(struct vm_area_struct *vma,
>> unsigned long start, unsigned long end);
>> diff --git a/mm/mmap.c b/mm/mmap.c
>> index 40248d84ad5f..d3c3c510f643 100644
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -136,6 +136,22 @@ void vma_set_page_prot(struct vm_area_struct *vma)
>> WRITE_ONCE(vma->vm_page_prot, vm_page_prot);
>> }
>>
>> +/*
>> + * Change backing file, only valid to use during initial VMA setup.
>> + */
>> +struct file *vma_set_file(struct vm_area_struct *vma, struct file *file)
>> +{
>> + if (file)
>> + get_file(file);
>> +
>> + swap(vma->vm_file, file);
>> +
>> + if (file)
>> + fput(file);
>> +
>> + return file;
>> +}
>> +
>> /*
>> * Requires inode->i_mapping->i_mmap_rwsem
>> */
>> --
>> 2.17.1
>>
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