On Tue, Feb 05, 2019 at 07:28:40PM +0900, Tetsuo Handa wrote:
> syzbot is hitting lockdep warnings [1][2][3]. This patch tries to fix
> the warning by eliminating ashmem_shrink_scan() => {shmem|vfs}_fallocate()
> sequence.
>
> [1]
> https://syzkaller.appspot.com/bug?id=87c399f6fa6955006080b24142e2ce7680295ad4
> [2]
> https://syzkaller.appspot.com/bug?id=7ebea492de7521048355fc84210220e1038a7908
> [3]
> https://syzkaller.appspot.com/bug?id=e02419c12131c24e2a957ea050c2ab6dcbbc3270
>
> Reported-by: syzbot <[email protected]>
> Reported-by: syzbot <[email protected]>
> Reported-by: syzbot <[email protected]>
> Signed-off-by: Tetsuo Handa <[email protected]>
> Cc: [email protected]
> ---
Please in the future, include some information about what changed from
previous patches, or atleast add a cover letter. And use patch revision
numbers. It is hard to know what changed from previous review.
This looks good to me,
Acked-by: Joel Fernandes (Google) <[email protected]>
thanks,
- Joel
> drivers/staging/android/ashmem.c | 25 ++++++++++++++++++++-----
> 1 file changed, 20 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/staging/android/ashmem.c
> b/drivers/staging/android/ashmem.c
> index 90a8a9f1ac7d..ade8438a827a 100644
> --- a/drivers/staging/android/ashmem.c
> +++ b/drivers/staging/android/ashmem.c
> @@ -75,6 +75,9 @@ struct ashmem_range {
> /* LRU list of unpinned pages, protected by ashmem_mutex */
> static LIST_HEAD(ashmem_lru_list);
>
> +static atomic_t ashmem_shrink_inflight = ATOMIC_INIT(0);
> +static DECLARE_WAIT_QUEUE_HEAD(ashmem_shrink_wait);
> +
> /*
> * long lru_count - The count of pages on our LRU list.
> *
> @@ -438,7 +441,6 @@ static int ashmem_mmap(struct file *file, struct
> vm_area_struct *vma)
> static unsigned long
> ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
> {
> - struct ashmem_range *range, *next;
> unsigned long freed = 0;
>
> /* We might recurse into filesystem code, so bail out if necessary */
> @@ -448,21 +450,33 @@ ashmem_shrink_scan(struct shrinker *shrink, struct
> shrink_control *sc)
> if (!mutex_trylock(&ashmem_mutex))
> return -1;
>
> - list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) {
> + while (!list_empty(&ashmem_lru_list)) {
> + struct ashmem_range *range =
> + list_first_entry(&ashmem_lru_list, typeof(*range), lru);
> loff_t start = range->pgstart * PAGE_SIZE;
> loff_t end = (range->pgend + 1) * PAGE_SIZE;
> + struct file *f = range->asma->file;
>
> - range->asma->file->f_op->fallocate(range->asma->file,
> - FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> - start, end - start);
> + get_file(f);
> + atomic_inc(&ashmem_shrink_inflight);
> range->purged = ASHMEM_WAS_PURGED;
> lru_del(range);
>
> freed += range_size(range);
> + mutex_unlock(&ashmem_mutex);
> + f->f_op->fallocate(f,
> + FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> + start, end - start);
> + fput(f);
> + if (atomic_dec_and_test(&ashmem_shrink_inflight))
> + wake_up_all(&ashmem_shrink_wait);
> + if (!mutex_trylock(&ashmem_mutex))
> + goto out;
> if (--sc->nr_to_scan <= 0)
> break;
> }
> mutex_unlock(&ashmem_mutex);
> +out:
> return freed;
> }
>
> @@ -713,6 +727,7 @@ 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;
> --
> 2.17.1
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