Messages in this thread | | | Date | Sat, 7 Oct 2023 06:20:43 +0200 | Subject | Re: BUG: KCSAN: data-race in btrfs_sync_log [btrfs] / btrfs_update_inode [btrfs] | From | Mirsad Goran Todorovac <> |
| |
On 10/6/2023 6:26 PM, David Sterba wrote: > On Thu, Sep 21, 2023 at 10:15:49PM +0200, Mirsad Todorovac wrote: >> Hi, >> >> On the vanilla 6.6-rc2 torvalds kernel KCSAN reported this data-race: >> >> [ 2690.990793] ================================================================== >> [ 2690.991470] BUG: KCSAN: data-race in btrfs_sync_log [btrfs] / btrfs_update_inode [btrfs] >> >> [ 2690.992804] write to 0xffff88811b57faf8 of 4 bytes by task 40555 on cpu 20: >> [ 2690.992815] btrfs_sync_log (/home/marvin/linux/kernel/torvalds2/fs/btrfs/tree-log.c:2964) btrfs >> [ 2690.993484] btrfs_sync_file (/home/marvin/linux/kernel/torvalds2/fs/btrfs/file.c:1954) btrfs >> [ 2690.994149] vfs_fsync_range (/home/marvin/linux/kernel/torvalds2/fs/sync.c:188) >> [ 2690.994161] __x64_sys_fsync (/home/marvin/linux/kernel/torvalds2/./include/linux/file.h:45 /home/marvin/linux/kernel/torvalds2/fs/sync.c:213 /home/marvin/linux/kernel/torvalds2/fs/sync.c:220 /home/marvin/linux/kernel/torvalds2/fs/sync.c:218 /home/marvin/linux/kernel/torvalds2/fs/sync.c:218) >> [ 2690.994172] do_syscall_64 (/home/marvin/linux/kernel/torvalds2/arch/x86/entry/common.c:50 /home/marvin/linux/kernel/torvalds2/arch/x86/entry/common.c:80) >> [ 2690.994186] entry_SYSCALL_64_after_hwframe (/home/marvin/linux/kernel/torvalds2/arch/x86/entry/entry_64.S:120) >> >> [ 2690.994203] read to 0xffff88811b57faf8 of 4 bytes by task 5338 on cpu 21: >> [ 2690.994214] btrfs_update_inode (/home/marvin/linux/kernel/torvalds2/fs/btrfs/transaction.h:175 /home/marvin/linux/kernel/torvalds2/fs/btrfs/inode.c:4016) btrfs >> [ 2690.994877] btrfs_finish_one_ordered (/home/marvin/linux/kernel/torvalds2/fs/btrfs/inode.c:4028 /home/marvin/linux/kernel/torvalds2/fs/btrfs/inode.c:3139) btrfs >> [ 2690.995541] btrfs_finish_ordered_io (/home/marvin/linux/kernel/torvalds2/fs/btrfs/inode.c:3230) btrfs >> [ 2690.996205] finish_ordered_fn (/home/marvin/linux/kernel/torvalds2/fs/btrfs/ordered-data.c:304) btrfs >> [ 2690.996871] btrfs_work_helper (/home/marvin/linux/kernel/torvalds2/fs/btrfs/async-thread.c:314) btrfs >> [ 2690.997539] process_one_work (/home/marvin/linux/kernel/torvalds2/kernel/workqueue.c:2630) >> [ 2690.997551] worker_thread (/home/marvin/linux/kernel/torvalds2/kernel/workqueue.c:2697 /home/marvin/linux/kernel/torvalds2/kernel/workqueue.c:2784) >> [ 2690.997562] kthread (/home/marvin/linux/kernel/torvalds2/kernel/kthread.c:388) >> [ 2690.997571] ret_from_fork (/home/marvin/linux/kernel/torvalds2/arch/x86/kernel/process.c:147) >> [ 2690.997583] ret_from_fork_asm (/home/marvin/linux/kernel/torvalds2/arch/x86/entry/entry_64.S:312) >> >> [ 2690.997598] value changed: 0x00000004 -> 0x00000005 >> >> [ 2690.997613] Reported by Kernel Concurrency Sanitizer on: >> [ 2690.997621] CPU: 21 PID: 5338 Comm: kworker/u65:7 Tainted: G L 6.6.0-rc2-kcsan-00143-gb5cbe7c00aa0 #41 >> [ 2690.997633] Hardware name: ASRock X670E PG Lightning/X670E PG Lightning, BIOS 1.21 04/26/2023 >> [ 2690.997640] Workqueue: btrfs-endio-write btrfs_work_helper [btrfs] >> [ 2690.998311] ================================================================== >> >> fs/btrfs/tree-log.c >> ------------------------------------- >> 2948 /* >> 2949 * We _must_ update under the root->log_mutex in order to make sure we >> 2950 * have a consistent view of the log root we are trying to commit at >> 2951 * this moment. >> 2952 * >> 2953 * We _must_ copy this into a local copy, because we are not holding the >> 2954 * log_root_tree->log_mutex yet. This is important because when we >> 2955 * commit the log_root_tree we must have a consistent view of the >> 2956 * log_root_tree when we update the super block to point at the >> 2957 * log_root_tree bytenr. If we update the log_root_tree here we'll race >> 2958 * with the commit and possibly point at the new block which we may not >> 2959 * have written out. >> 2960 */ >> 2961 btrfs_set_root_node(&log->root_item, log->node); >> 2962 memcpy(&new_root_item, &log->root_item, sizeof(new_root_item)); >> 2963 >> 2964 → root->log_transid++; >> 2965 log->log_transid = root->log_transid; >> 2966 root->log_start_pid = 0; >> 2967 /* >> 2968 * IO has been started, blocks of the log tree have WRITTEN flag set >> 2969 * in their headers. new modifications of the log will be written to >> 2970 * new positions. so it's safe to allow log writers to go in. >> 2971 */ >> 2972 mutex_unlock(&root->log_mutex); >> >> fs/btrfs/transaction.h >> ---------------------------------- >> 170 static inline void btrfs_set_inode_last_trans(struct btrfs_trans_handle *trans, >> 171 struct btrfs_inode *inode) >> 172 { >> 173 spin_lock(&inode->lock); >> 174 inode->last_trans = trans->transaction->transid; >> 175 inode->last_sub_trans = inode->root->log_transid; >> 176 inode->last_log_commit = inode->last_sub_trans - 1; >> 177 spin_unlock(&inode->lock); >> 178 } >> >> I am not certain whether the reader and writer side contend for the same lock, but it >> seems that on the safe side would be putting the reader into READ_ONCE() to get a consistent >> value?: > > Filipe send a series adding the READ_ONCE/WRITE_ONCE annotations for the > log_transid (and more): > https://lore.kernel.org/linux-btrfs/cover.1696415673.git.fdmanana@suse.com/ > > This will appear in linux-next soon.
That looks promising and I will test whether it pleases KCSAN in my setup (it looks like it should). I consider filesystem data integrity a paramount.
If you found this bug report helpful, consider adding:
Reported-by: Mirsad Todorovac <mirsad.todorovac@alu.unizg.hr>
Best regards, Mirsad Todorovac
-- Mirsad Todorovac Sistem inženjer Grafički fakultet | Akademija likovnih umjetnosti Sveučilište u Zagrebu
System engineer Faculty of Graphic Arts | Academy of Fine Arts University of Zagreb, Republic of Croatia tel. +385 (0)1 3711 451 mob. +385 91 57 88 355
| |