The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From fb4415a12632f0b9078a0aa80c16745d48fcfc74 Mon Sep 17 00:00:00 2001

From: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Date: Tue, 5 Feb 2019 19:28:40 +0900 Subject: [PATCH] staging: android: ashmem: Don't call fallocate() with ashmem_mutex held.

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=87c399f6fa6955006080b24142e2ce7680295ad... [2] https://syzkaller.appspot.com/bug?id=7ebea492de7521048355fc84210220e1038a790... [3] https://syzkaller.appspot.com/bug?id=e02419c12131c24e2a957ea050c2ab6dcbbc327...

Reported-by: syzbot syzbot+a76129f18c89f3e2ddd4@syzkaller.appspotmail.com Reported-by: syzbot syzbot+148c2885d71194f18d28@syzkaller.appspotmail.com Reported-by: syzbot syzbot+4b8b031b89e6b96c4b2e@syzkaller.appspotmail.com Signed-off-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Cc: stable@vger.kernel.org Acked-by: Joel Fernandes (Google) joel@joelfernandes.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c index 92f42cea5ae4..5d5b091b957a 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. * @@ -439,7 +442,6 @@ 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 */ @@ -449,21 +451,33 @@ 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; }

@@ -714,6 +728,7 @@ 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;