On Tue, Jan 22, 2019 at 11:02 AM Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote: > > On 2018/09/22 8:21, Andrew Morton wrote: > > On Thu, 20 Sep 2018 19:33:15 -0400 Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote: > > > >> On Thu, Sep 20, 2018 at 5:12 PM Todd Kjos <tkjos@xxxxxxxxxx> wrote: > >>> > >>> +Joel Fernandes > >>> > >>> On Thu, Sep 20, 2018 at 2:11 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > >>>> > >>>> > >>>> Thanks. Let's cc the ashmem folks. > >>>> > >> > >> This should be fixed by https://patchwork.kernel.org/patch/10572477/ > >> > >> It has Neil Brown's Reviewed-by but looks like didn't yet appear in > >> anyone's tree, could Greg take this patch? > > > > All is well. That went into mainline yesterday, with a cc:stable. > > > > This problem was not fixed at all. There are at least 2 other open deadlocks involving ashmem: https://syzkaller.appspot.com/bug?extid=148c2885d71194f18d28 https://syzkaller.appspot.com/bug?extid=4b8b031b89e6b96c4b2e Does this fix any of these too? > Why do we need to call fallocate() synchronously with ashmem_mutex held? > Why can't we call fallocate() asynchronously from WQ_MEM_RECLAIM workqueue > context so that we can call fallocate() with ashmem_mutex not held? > > I don't know how ashmem works, but as far as I can guess, offloading is > possible as long as other operations which depend on the completion of > fallocate() operation (e.g. read()/mmap(), querying/changing pinned status) > wait for completion of asynchronous fallocate() operation (like a draft > patch shown below is doing). > > --- > drivers/staging/android/ashmem.c | 50 ++++++++++++++++++++++++++++---- > 1 file changed, 45 insertions(+), 5 deletions(-) > > diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c > index 90a8a9f1ac7d..1a890c43a10a 100644 > --- a/drivers/staging/android/ashmem.c > +++ b/drivers/staging/android/ashmem.c > @@ -75,6 +75,17 @@ struct ashmem_range { > /* LRU list of unpinned pages, protected by ashmem_mutex */ > static LIST_HEAD(ashmem_lru_list); > > +static struct workqueue_struct *ashmem_wq; > +static atomic_t ashmem_shrink_inflight = ATOMIC_INIT(0); > +static DECLARE_WAIT_QUEUE_HEAD(ashmem_shrink_wait); > + > +struct ashmem_shrink_work { > + struct work_struct work; > + struct file *file; > + loff_t start; > + loff_t end; > +}; > + > /* > * long lru_count - The count of pages on our LRU list. > * > @@ -292,6 +303,7 @@ static ssize_t ashmem_read_iter(struct kiocb *iocb, struct iov_iter *iter) > int ret = 0; > > mutex_lock(&ashmem_mutex); > + wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight)); > > /* If size is not set, or set to 0, always return EOF. */ > if (asma->size == 0) > @@ -359,6 +371,7 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma) > int ret = 0; > > mutex_lock(&ashmem_mutex); > + wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight)); > > /* user needs to SET_SIZE before mapping */ > if (!asma->size) { > @@ -421,6 +434,19 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma) > return ret; > } > > +static void ashmem_shrink_worker(struct work_struct *work) > +{ > + struct ashmem_shrink_work *w = container_of(work, typeof(*w), work); > + > + w->file->f_op->fallocate(w->file, > + FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, > + w->start, w->end - w->start); > + fput(w->file); > + kfree(w); > + if (atomic_dec_and_test(&ashmem_shrink_inflight)) > + wake_up_all(&ashmem_shrink_wait); > +} > + > /* > * ashmem_shrink - our cache shrinker, called from mm/vmscan.c > * > @@ -449,12 +475,18 @@ ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) > return -1; > > list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) { > - loff_t start = range->pgstart * PAGE_SIZE; > - loff_t end = (range->pgend + 1) * PAGE_SIZE; > + struct ashmem_shrink_work *w = kzalloc(sizeof(*w), GFP_ATOMIC); > + > + if (!w) > + break; > + INIT_WORK(&w->work, ashmem_shrink_worker); > + w->file = range->asma->file; > + get_file(w->file); > + w->start = range->pgstart * PAGE_SIZE; > + w->end = (range->pgend + 1) * PAGE_SIZE; > + atomic_inc(&ashmem_shrink_inflight); > + queue_work(ashmem_wq, &w->work); > > - range->asma->file->f_op->fallocate(range->asma->file, > - FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, > - start, end - start); > range->purged = ASHMEM_WAS_PURGED; > lru_del(range); > > @@ -713,6 +745,7 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd, > return -EFAULT; > > mutex_lock(&ashmem_mutex); > + wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight)); > > if (!asma->file) > goto out_unlock; > @@ -883,8 +916,15 @@ static int __init ashmem_init(void) > goto out_free2; > } > > + ashmem_wq = alloc_workqueue("ashmem_wq", WQ_MEM_RECLAIM, 0); > + if (!ashmem_wq) { > + pr_err("failed to create workqueue\n"); > + goto out_demisc; > + } > + > ret = register_shrinker(&ashmem_shrinker); > if (ret) { > + destroy_workqueue(ashmem_wq); > pr_err("failed to register shrinker!\n"); > goto out_demisc; > } > -- > 2.17.1
