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Tsirkin" , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Maxime Coquelin X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: D2CF32000E X-Stat-Signature: f39k7qu8kgf6xo7krfaxzopgr61g8565 X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1722224554-144497 X-HE-Meta: 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 qswNmf4o yH5M95dbn1RpebZ0uNyNEFGBK/AV72JkdXXO+GYFRgrwXsqFv/kGydP5sULOhtHlvKwNrEa3D4adH35f/tjDfftVsKfoKgSt+3ptsaptPAYxgBfVAounLbIyeATzPlpZWehH7n7UOB667iftehC4ZWJM48coauRytfsBpsIiSNx6gPk0qTNs4XEvgFyUg1ot+Q9YpR04u9tLUNUcSvZmDAvlPo+uWYuuEWUUF1+ZKMSvtVouL3O4zje0vipTONpJWDRYENcZkwtyxNKZW9fPJBOwz9FT6ipGh1xbHAXj7sz+rm1jp4Wb3Ep645W6h271XdVnxPxMVJL7slickMF27OB3uejPJk7e3WnxHwE9XAsKB2QfdOr8TGhehqRYSFuvomRQHNw1iiT6X8aMOH+sdLDgO75z07R4cv3RHPWTkURK2ojd0vmflk7c6tsUDWt4ji11PzmFfl8fpkx8= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jul 25, 2024 at 3:00=E2=80=AFPM Barry Song <21cnbao@gmail.com> wrot= e: > > On Thu, Jul 25, 2024 at 6:08=E2=80=AFPM Michal Hocko wr= ote: > > > > On Thu 25-07-24 10:50:45, Barry Song wrote: > > > On Thu, Jul 25, 2024 at 12:27=E2=80=AFAM Michal Hocko wrote: > > > > > > > > On Wed 24-07-24 20:55:40, Barry Song wrote: > > [...] > > > > > diff --git a/drivers/vdpa/vdpa_user/iova_domain.c b/drivers/vdpa/= vdpa_user/iova_domain.c > > > > > index 791d38d6284c..eff700e5f7a2 100644 > > > > > --- a/drivers/vdpa/vdpa_user/iova_domain.c > > > > > +++ b/drivers/vdpa/vdpa_user/iova_domain.c > > > > > @@ -287,28 +287,44 @@ void vduse_domain_remove_user_bounce_pages(= struct vduse_iova_domain *domain) > > > > > { > > > > > struct vduse_bounce_map *map; > > > > > unsigned long i, count; > > > > > + struct page **pages =3D NULL; > > > > > > > > > > write_lock(&domain->bounce_lock); > > > > > if (!domain->user_bounce_pages) > > > > > goto out; > > > > > - > > > > > count =3D domain->bounce_size >> PAGE_SHIFT; > > > > > + write_unlock(&domain->bounce_lock); > > > > > + > > > > > + pages =3D kmalloc_array(count, sizeof(*pages), GFP_KERNEL |= __GFP_NOFAIL); > > > > > + for (i =3D 0; i < count; i++) > > > > > + pages[i] =3D alloc_page(GFP_KERNEL | __GFP_NOFAIL); > > > > > > > > AFAICS vduse_domain_release calls this function with > > > > spin_lock(&domain->iotlb_lock) so dropping &domain->bounce_lock is = not > > > > sufficient. > > > > > > yes. this is true: > > > > > > static int vduse_domain_release(struct inode *inode, struct file *fil= e) > > > { > > > struct vduse_iova_domain *domain =3D file->private_data; > > > > > > spin_lock(&domain->iotlb_lock); > > > vduse_iotlb_del_range(domain, 0, ULLONG_MAX); > > > vduse_domain_remove_user_bounce_pages(domain); > > > vduse_domain_free_kernel_bounce_pages(domain); > > > spin_unlock(&domain->iotlb_lock); > > > put_iova_domain(&domain->stream_iovad); > > > put_iova_domain(&domain->consistent_iovad); > > > vhost_iotlb_free(domain->iotlb); > > > vfree(domain->bounce_maps); > > > kfree(domain); > > > > > > return 0; > > > } > > > > > > This is quite a pain. I admit I don't have knowledge of this driver, = and I don't > > > think it's safe to release two locks and then reacquire them. The sit= uation is > > > rather complex. Therefore, I would prefer if the VDPA maintainers cou= ld > > > take the lead in implementing a proper fix. > > > > Would it be possible to move all that work to a deferred context? > > My understanding is that we need to be aware of both the iotlb_lock and > bounce_lock to implement the correct changes. As long as we still need > to acquire these two locks in a deferred context, there doesn't seem to > be any difference. > > I can do the memory pre-allocation before spin_lock(&domain->iotlb_lock), > but I have no knowledge whether the "count" will change after I make > the preallocation. > > diff --git a/drivers/vdpa/vdpa_user/iova_domain.c > b/drivers/vdpa/vdpa_user/iova_domain.c > index 791d38d6284c..7ec87ef33d42 100644 > --- a/drivers/vdpa/vdpa_user/iova_domain.c > +++ b/drivers/vdpa/vdpa_user/iova_domain.c > @@ -544,9 +544,12 @@ static int vduse_domain_release(struct inode > *inode, struct file *file) > { > struct vduse_iova_domain *domain =3D file->private_data; > > + struct page **pages; > + spin_lock(&domain->iotlb_lock); maybe also + bounce_lock? > + count =3D domain->bounce_size >> PAGE_SHIFT; > + spin_unlock(&domain->iotlb_lock); We probably don't need any lock here as bounce_size won't be changed . > + > + preallocate_count_pages(pages, count); > + > .... > spin_lock(&domain->iotlb_lock); > vduse_iotlb_del_range(domain, 0, ULLONG_MAX); > - vduse_domain_remove_user_bounce_pages(domain); > + vduse_domain_remove_user_bounce_pages(domain, pages); > vduse_domain_free_kernel_bounce_pages(domain); > spin_unlock(&domain->iotlb_lock); > put_iova_domain(&domain->stream_iovad); This seems to work. Thanks > > > > -- > > Michal Hocko > > SUSE Labs >