Thu, 26 Dec 2019 13:25:09 -0800 > syzbot found the following crash on: > > HEAD commit: 46cf053e Linux 5.5-rc3 > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=162124aee00000 > kernel config: https://syzkaller.appspot.com/x/.config?x=ed9d672709340e35 > dashboard link: https://syzkaller.appspot.com/bug?extid=7a0d9d0b26efefe61780 > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > Unfortunately, I don't have any reproducer for this crash yet. > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+7a0d9d0b26efefe61780@xxxxxxxxxxxxxxxxxxxxxxxxx > > ====================================================== > WARNING: possible circular locking dependency detected > 5.5.0-rc3-syzkaller #0 Not tainted > ------------------------------------------------------ > kswapd0/1852 is trying to acquire lock: > ffff888098919cd8 (&sb->s_type->i_mutex_key#13){+.+.}, at: inode_lock > include/linux/fs.h:791 [inline] > ffff888098919cd8 (&sb->s_type->i_mutex_key#13){+.+.}, at: > shmem_fallocate+0x15a/0xd40 mm/shmem.c:2735 > > but task is already holding lock: > ffffffff89a41e00 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x30 > mm/page_alloc.c:4922 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #1 (fs_reclaim){+.+.}: > __fs_reclaim_acquire mm/page_alloc.c:4084 [inline] > fs_reclaim_acquire.part.0+0x24/0x30 mm/page_alloc.c:4095 > fs_reclaim_acquire mm/page_alloc.c:4695 [inline] > prepare_alloc_pages mm/page_alloc.c:4692 [inline] > __alloc_pages_nodemask+0x52d/0x910 mm/page_alloc.c:4744 > alloc_pages_vma+0xdd/0x620 mm/mempolicy.c:2170 > shmem_alloc_page+0xc0/0x180 mm/shmem.c:1499 > shmem_alloc_and_acct_page+0x165/0x990 mm/shmem.c:1524 > shmem_getpage_gfp+0x56d/0x29a0 mm/shmem.c:1838 > shmem_getpage mm/shmem.c:154 [inline] > shmem_write_begin+0x105/0x1e0 mm/shmem.c:2487 > generic_perform_write+0x23b/0x540 mm/filemap.c:3309 > __generic_file_write_iter+0x25e/0x630 mm/filemap.c:3438 > generic_file_write_iter+0x420/0x68e mm/filemap.c:3470 > call_write_iter include/linux/fs.h:1902 [inline] > new_sync_write+0x4d3/0x770 fs/read_write.c:483 > __vfs_write+0xe1/0x110 fs/read_write.c:496 > vfs_write+0x268/0x5d0 fs/read_write.c:558 > ksys_write+0x14f/0x290 fs/read_write.c:611 > __do_sys_write fs/read_write.c:623 [inline] > __se_sys_write fs/read_write.c:620 [inline] > __x64_sys_write+0x73/0xb0 fs/read_write.c:620 > do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > -> #0 (&sb->s_type->i_mutex_key#13){+.+.}: > check_prev_add kernel/locking/lockdep.c:2476 [inline] > check_prevs_add kernel/locking/lockdep.c:2581 [inline] > validate_chain kernel/locking/lockdep.c:2971 [inline] > __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3955 > lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4485 > down_write+0x93/0x150 kernel/locking/rwsem.c:1534 > inode_lock include/linux/fs.h:791 [inline] > shmem_fallocate+0x15a/0xd40 mm/shmem.c:2735 > ashmem_shrink_scan drivers/staging/android/ashmem.c:462 [inline] > ashmem_shrink_scan+0x370/0x510 drivers/staging/android/ashmem.c:437 > do_shrink_slab+0x40f/0xad0 mm/vmscan.c:526 > shrink_slab mm/vmscan.c:687 [inline] > shrink_slab+0x19a/0x680 mm/vmscan.c:660 > shrink_node_memcgs mm/vmscan.c:2687 [inline] > shrink_node+0x46a/0x1ad0 mm/vmscan.c:2791 > kswapd_shrink_node mm/vmscan.c:3539 [inline] > balance_pgdat+0x7c8/0x11f0 mm/vmscan.c:3697 > kswapd+0x5c3/0xf30 mm/vmscan.c:3948 > kthread+0x361/0x430 kernel/kthread.c:255 > ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352 > > other info that might help us debug this: > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(fs_reclaim); > lock(&sb->s_type->i_mutex_key#13); > lock(fs_reclaim); > lock(&sb->s_type->i_mutex_key#13); > > *** DEADLOCK *** > > 2 locks held by kswapd0/1852: > #0: ffffffff89a41e00 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x30 mm/page_alloc.c:4922 > #1: ffffffff89a1f948 (shrinker_rwsem){++++}, at: shrink_slab mm/vmscan.c:677 [inline] > #1: ffffffff89a1f948 (shrinker_rwsem){++++}, at: shrink_slab+0xe6/0x680 mm/vmscan.c:660 > > stack backtrace: > CPU: 0 PID: 1852 Comm: kswapd0 Not tainted 5.5.0-rc3-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x197/0x210 lib/dump_stack.c:118 > print_circular_bug.isra.0.cold+0x163/0x172 kernel/locking/lockdep.c:1685 > check_noncircular+0x32e/0x3e0 kernel/locking/lockdep.c:1809 > check_prev_add kernel/locking/lockdep.c:2476 [inline] > check_prevs_add kernel/locking/lockdep.c:2581 [inline] > validate_chain kernel/locking/lockdep.c:2971 [inline] > __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3955 > lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4485 > down_write+0x93/0x150 kernel/locking/rwsem.c:1534 > inode_lock include/linux/fs.h:791 [inline] > shmem_fallocate+0x15a/0xd40 mm/shmem.c:2735 > ashmem_shrink_scan drivers/staging/android/ashmem.c:462 [inline] > ashmem_shrink_scan+0x370/0x510 drivers/staging/android/ashmem.c:437 > do_shrink_slab+0x40f/0xad0 mm/vmscan.c:526 > shrink_slab mm/vmscan.c:687 [inline] > shrink_slab+0x19a/0x680 mm/vmscan.c:660 > shrink_node_memcgs mm/vmscan.c:2687 [inline] > shrink_node+0x46a/0x1ad0 mm/vmscan.c:2791 > kswapd_shrink_node mm/vmscan.c:3539 [inline] > balance_pgdat+0x7c8/0x11f0 mm/vmscan.c:3697 > kswapd+0x5c3/0xf30 mm/vmscan.c:3948 > kthread+0x361/0x430 kernel/kthread.c:255 > ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352 Simply move punch-hole out of page reclaiming context to avoid deadlock. --- a/drivers/staging/android/ashmem.c +++ b/drivers/staging/android/ashmem.c @@ -24,6 +24,7 @@ #include <linux/bitops.h> #include <linux/mutex.h> #include <linux/shmem_fs.h> +#include <linux/workqueue.h> #include "ashmem.h" #define ASHMEM_NAME_PREFIX "dev/ashmem/" @@ -70,6 +71,7 @@ struct ashmem_range { size_t pgstart; size_t pgend; unsigned int purged; + struct work_struct work; }; /* LRU list of unpinned pages, protected by ashmem_mutex */ @@ -201,6 +203,7 @@ static void range_del(struct ashmem_rang list_del(&range->unpinned); if (range_on_lru(range)) lru_del(range); + flush_work(&range->work); kmem_cache_free(ashmem_range_cachep, range); } @@ -419,6 +422,21 @@ out: return ret; } +static void ashmem_shrink_workfn(struct work_struct *__work) +{ + struct ashmem_range *range = container_of(__work, + struct ashmem_range, work); + loff_t start = range->pgstart * PAGE_SIZE; + loff_t end = (range->pgend + 1) * PAGE_SIZE; + struct file *f = range->asma->file; + + 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); +} + /* * ashmem_shrink - our cache shrinker, called from mm/vmscan.c * @@ -448,8 +466,6 @@ ashmem_shrink_scan(struct shrinker *shri 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; get_file(f); @@ -459,12 +475,9 @@ ashmem_shrink_scan(struct shrinker *shri 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); + + queue_work(system_unbound_wq, &range->work); + if (!mutex_trylock(&ashmem_mutex)) goto out; if (--sc->nr_to_scan <= 0) @@ -729,6 +742,7 @@ static int ashmem_pin_unpin(struct ashme range = kmem_cache_zalloc(ashmem_range_cachep, GFP_KERNEL); if (!range) return -ENOMEM; + INIT_WORK(&range->work, ashmem_shrink_workfn); } mutex_lock(&ashmem_mutex);
