syzbot


KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put

Status: moderation: reported on 2025/06/04 06:15
Subsystems: exfat
[Documentation on labels]
Reported-by: syzbot+a75b41b3a6c914982c27@syzkaller.appspotmail.com
First crash: 280d, last: 1d12h
✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision Error
f15b7960-8139-4191-8fb9-d46f955c999b repro KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put 2026/03/10 14:06
4306723c-b4be-45c1-b667-6fabffefde18 assessment-kcsan Benign: ❌  Confident: ✅  KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put 2026/01/15 04:12 2026/01/15 04:12 2026/01/15 04:34 a9d6a79219801d2130df3b1a792c57f0e5428e9f

Sample crash report:
==================================================================
BUG: KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put

write to 0xffff88810bacbb36 of 2 bytes by task 3690 on cpu 0:
 fat16_ent_put+0x28/0x60 fs/fat/fatent.c:183
 fat_free_clusters+0x2cc/0x8a0 fs/fat/fatent.c:597
 fat_free fs/fat/file.c:377 [inline]
 fat_truncate_blocks+0x510/0x5a0 fs/fat/file.c:395
 fat_write_failed fs/fat/inode.c:219 [inline]
 fat_write_end+0xba/0x160 fs/fat/inode.c:247
 generic_perform_write+0x311/0x490 mm/filemap.c:4340
 __generic_file_write_iter+0x9e/0x120 mm/filemap.c:4436
 generic_file_write_iter+0x8d/0x310 mm/filemap.c:4462
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x5a6/0x9f0 fs/read_write.c:688
 ksys_write+0xdc/0x1a0 fs/read_write.c:740
 __do_sys_write fs/read_write.c:751 [inline]
 __se_sys_write fs/read_write.c:748 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:748
 x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810bacba00 of 512 bytes by task 55 on cpu 1:
 memcpy_from_iter lib/iov_iter.c:85 [inline]
 iterate_bvec include/linux/iov_iter.h:123 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:306 [inline]
 iterate_and_advance include/linux/iov_iter.h:330 [inline]
 __copy_from_iter lib/iov_iter.c:261 [inline]
 copy_folio_from_iter_atomic+0x75f/0x1170 lib/iov_iter.c:491
 generic_perform_write+0x2c1/0x490 mm/filemap.c:4337
 shmem_file_write_iter+0xc5/0xf0 mm/shmem.c:3502
 lo_rw_aio+0x67d/0x730 drivers/block/loop.c:-1
 do_req_filebacked drivers/block/loop.c:-1 [inline]
 loop_handle_cmd drivers/block/loop.c:1925 [inline]
 loop_process_work+0x56c/0xac0 drivers/block/loop.c:1960
 loop_workfn+0x31/0x40 drivers/block/loop.c:1984
 process_one_work kernel/workqueue.c:3275 [inline]
 process_scheduled_works+0x4de/0x9e0 kernel/workqueue.c:3358
 worker_thread+0x581/0x770 kernel/workqueue.c:3439
 kthread+0x22a/0x280 kernel/kthread.c:436
 ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 55 Comm: kworker/u8:4 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: loop4 loop_workfn
==================================================================

Crashes (103):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/10 01:46 upstream 1f318b96cc84 6972f302 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/03/09 19:39 upstream 1f318b96cc84 176bead5 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/03/08 05:02 upstream c23719abc330 5cb44a80 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/03/06 21:56 upstream 651690480a96 41d8037d .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/03/06 13:38 upstream 5ee8dbf54602 41d8037d .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/03/06 03:04 upstream 5ee8dbf54602 31e9c887 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/02/28 18:07 upstream 2f9339c052bd 43249bac .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/02/27 06:37 upstream 3f4a08e64442 a2f13f71 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/02/23 03:07 upstream 6de23f81a5e0 6e7b5511 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/02/14 21:41 upstream 3e48a11675c5 1e62d198 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/02/07 03:04 upstream 2687c848e578 f20fc9f9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/02/06 12:05 upstream b7ff7151e653 97745f52 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/02/05 18:54 upstream 8fdb05de0e2d 4936e85c .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/02/04 12:44 upstream 5fd0a1df5d05 42b01fab .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/02/02 10:35 upstream 18f7fcd5e69a 018ebef2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/01/31 02:41 upstream 283073725700 c75a2f6e .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2026/01/27 23:21 upstream 1f97d9dcf536 3029c699 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/12/31 21:39 upstream 349bd28a86f2 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/12/31 07:28 upstream c8ebd433459b d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/12/24 20:08 upstream ccd1cdca5cd4 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/12/24 20:07 upstream ccd1cdca5cd4 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/11/15 09:27 upstream 7a0892d2836e f7988ea4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/11/10 19:09 upstream 4ea7c1717f3f 4e1406b4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/11/10 02:55 upstream e9a6fb0bcdd7 4e1406b4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/11/09 00:10 upstream 7bb4d6512545 4e1406b4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/11/05 21:07 upstream 1c353dc8d962 a6c9c731 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/11/01 06:36 upstream ba36dd5ee6fd 2c50b6a9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/10/24 11:27 upstream 6fab32bb6508 c0460fcd .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/10/17 09:55 upstream 98ac9cc4b445 7adf5298 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/10/15 17:51 upstream 1f4a222b0e33 19568248 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/10/10 20:06 upstream 917167ed1211 ff1712fe .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/10/07 22:51 upstream 971199ad2a0f 7e2882b3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/10/02 02:28 upstream 080ffb4bec4d 267f56c6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/09/22 10:39 upstream 07e27ad16399 0ac7291c .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/09/21 21:04 upstream 2d5bd41a4505 67c37560 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/09/21 07:44 upstream f975f08c2e89 67c37560 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/09/16 23:43 upstream 5aca7966d2a7 e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/09/15 11:31 upstream f83ec76bf285 e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/09/14 22:02 upstream 79e8447ec662 e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/09/13 19:03 upstream 5cd64d4f9268 e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/09/03 20:34 upstream ec299e4dc21e 96a211bc .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/08/26 16:16 upstream fab1beda7597 e12e5ba4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/08/25 16:58 upstream b6add54ba618 bf27483f .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/08/22 04:16 upstream 3957a5720157 bf27483f .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
2025/06/04 06:14 upstream 5abc7438f1e9 a30356b7 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_folio_from_iter_atomic / fat16_ent_put
* Struck through repros no longer work on HEAD.