From b8d048b739007a0fd370b52033cb7357f960e4a0 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Tue, 5 Feb 2019 19:28:40 +0900 Subject: [PATCH] staging: android: ashmem: Don't call fallocate() with ashmem_mutex held. commit fb4415a12632f0b9078a0aa80c16745d48fcfc74 upstream. 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 Reported-by: syzbot Reported-by: syzbot Signed-off-by: Tetsuo Handa Cc: stable@vger.kernel.org Acked-by: Joel Fernandes (Google) Signed-off-by: Greg Kroah-Hartman --- 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 a880b5c..1cc451b 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 @@ out: 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; -- 2.7.4