On 2018年04月12日 21:35, David Sterba wrote: > On Thu, Apr 12, 2018 at 06:00:02PM +0800, Qu Wenruo wrote: >> When looping btrfs/074 with many cpus (>= 8), it's possible to trigger >> kernel warning due to first key verification: >> >> [ 4239.523446] WARNING: CPU: 5 PID: 2381 at fs/btrfs/disk-io.c:460 >> btree_read_extent_buffer_pages+0x1ad/0x210 >> [ 4239.523830] Modules linked in: >> [ 4239.524630] RIP: 0010:btree_read_extent_buffer_pages+0x1ad/0x210 >> [ 4239.527101] Call Trace: >> [ 4239.527251] read_tree_block+0x42/0x70 >> [ 4239.527434] read_node_slot+0xd2/0x110 >> [ 4239.527632] push_leaf_right+0xad/0x1b0 >> [ 4239.527809] split_leaf+0x4ea/0x700 >> [ 4239.527988] ? leaf_space_used+0xbc/0xe0 >> [ 4239.528192] ? btrfs_set_lock_blocking_rw+0x99/0xb0 >> [ 4239.528416] btrfs_search_slot+0x8cc/0xa40 >> [ 4239.528605] btrfs_insert_empty_items+0x71/0xc0 >> [ 4239.528798] __btrfs_run_delayed_refs+0xa98/0x1680 >> [ 4239.529013] btrfs_run_delayed_refs+0x10b/0x1b0 >> [ 4239.529205] btrfs_commit_transaction+0x33/0xaf0 >> [ 4239.529445] ? start_transaction+0xa8/0x4f0 >> [ 4239.529630] btrfs_alloc_data_chunk_ondemand+0x1b0/0x4e0 >> [ 4239.529833] btrfs_check_data_free_space+0x54/0xa0 >> [ 4239.530045] btrfs_delalloc_reserve_space+0x25/0x70 >> [ 4239.531907] btrfs_direct_IO+0x233/0x3d0 >> [ 4239.532098] generic_file_direct_write+0xcb/0x170 >> [ 4239.532296] btrfs_file_write_iter+0x2bb/0x5f4 >> [ 4239.532491] aio_write+0xe2/0x180 >> [ 4239.532669] ? lock_acquire+0xac/0x1e0 >> [ 4239.532839] ? __might_fault+0x3e/0x90 >> [ 4239.533032] do_io_submit+0x594/0x860 >> [ 4239.533223] ? do_io_submit+0x594/0x860 >> [ 4239.533398] SyS_io_submit+0x10/0x20 >> [ 4239.533560] ? SyS_io_submit+0x10/0x20 >> [ 4239.533729] do_syscall_64+0x75/0x1d0 >> [ 4239.533979] entry_SYSCALL_64_after_hwframe+0x42/0xb7 >> [ 4239.534182] RIP: 0033:0x7f8519741697 >> >> The possibility is low, around 4~7/128 runs with 8 cores. >> The problem here is, at btree_read_extent_buffer_pages() we don't have >> acquired read/write lock on that extent buffer, only basic info like >> level/bytenr is reliable. >> >> To get correct first key, we must require at least read lock for that >> extent buffer, which can't be done in btree_read_extent_buffer_pages(), >> but deep into core btree operation code. >> >> This patch will remove the unreliable first key check to avoid false >> alerts, and allow later patch to re-implement first key check correctly. > > We'll have to disable the first key check in a less intrusive way, eg. > taking a shortcut in verify_level_key.
OK, I'll take the alternative solution (method 3) in v4.17 release cycle to bring a small but with less coverage. Originally I have 3 ways to fix the false alerts 1) Proper lock handler The one I used in 2nd patch, as you can see it needs proper lock context and a lot of new error handlers. But with best coverage, not only covers new tree blocks read from disk, but also any live tree blocks. (But helps me to understand the whole tree locking mechanism) 2) Move check to btree_readpage_end_io_hook() So no race, and only covers tree block read from disk. (and only done once) The problem is, we need pass key and level all the way to submit_bio_hook(), I don't think it would be an easy work. 3) Skip check for tree blocks of current trans Similar coverage of 2), but may still do extra (duplicated) check each time we call read_tree_block(). The idea is to only check first_key if the transid <= fs_info->last_committed_transid. So we shouldn't meet any race. For 1) or 2) I'll double consider their possibility and benefit in next release cycle. > The patch has was added in > recent pull, I'm not going to do full a revert now. Well, this patch is not completely reverting, but still pretty much reverts half of original patch. I'll use method 3 to bring the modification to minimal. Thanks, Qu > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html