KCSAN: data-race in loop_assign_backing_file / shmem_write

ID	Workflow	Result	Correct	Bug	Created	Started	Finished	Revision	Error
52e3ef19-a567-4376-8774-da802ec65696	assessment-kcsan	Benign: ✅ Confident: ✅	❓	KCSAN: data-race in loop_assign_backing_file / shmem_write_begin (2)	2026/02/25 02:13	2026/02/25 02:13	2026/02/25 02:23	305c0ec5cd886e2d13738e28e1b2df9b0ec20fc9
b9c2bced-41c4-4f56-bd08-68c693598888	assessment-kcsan		💥	KCSAN: data-race in loop_assign_backing_file / shmem_write_begin (2)	2026/01/23 07:50	2026/01/23 07:50	2026/01/23 07:52	499a21815ec0ab13dbfc80e05fc32aadbc482145	failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "16" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/usr/local/google/home/dvyukov/syzkaller/workdir/cache/build/ad58fd55d5f9d933ea7c043fd238d534c6a70c00" "bzImage" "compile_commands.json"]: exit status 2

Kernel	Title	Rank 🛈	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
upstream	KCSAN: data-race in loop_assign_backing_file / shmem_write_begin block	6				1	141d	141d	0/29	auto-obsoleted due to no activity on 2025/12/18 18:20

Kernel

Title

Rank 🛈

upstream

KCSAN: data-race in loop_assign_backing_file / shmem_write_begin block

141d

0/29

auto-obsoleted due to no activity on 2025/12/18 18:20

================================================================== BUG: KCSAN: data-race in loop_assign_backing_file / shmem_write_begin write to 0xffff88811b036510 of 4 bytes by task 4620 on cpu 0: mapping_set_gfp_mask include/linux/pagemap.h:377 [inline] loop_assign_backing_file+0x80/0x210 drivers/block/loop.c:513 loop_configure+0x720/0x9c0 drivers/block/loop.c:1060 lo_ioctl+0x5ac/0x13a0 drivers/block/loop.c:1563 blkdev_ioctl+0x387/0x460 block/ioctl.c:792 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583 x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f read to 0xffff88811b036510 of 4 bytes by task 4615 on cpu 1: mapping_gfp_mask include/linux/pagemap.h:361 [inline] shmem_get_folio mm/shmem.c:2663 [inline] shmem_write_begin+0xdc/0x1f0 mm/shmem.c:3315 generic_perform_write+0x183/0x490 mm/filemap.c:4314 shmem_file_write_iter+0xc5/0xf0 mm/shmem.c:3490 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x5a6/0x9f0 fs/read_write.c:686 ksys_write+0xdc/0x1a0 fs/read_write.c:738 __do_sys_write fs/read_write.c:749 [inline] __se_sys_write fs/read_write.c:746 [inline] __x64_sys_write+0x40/0x50 fs/read_write.c:746 x64_sys_call+0x2847/0x3000 arch/x86/include/generated/asm/syscalls_64.h:2 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f value changed: 0x00100cca -> 0x00100c0a Reported by Kernel Concurrency Sanitizer on: CPU: 1 UID: 0 PID: 4615 Comm: syz.3.370 Not tainted syzkaller #0 PREEMPT(voluntary) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 ==================================================================

Crashes (1):
Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Assets (help?)	Manager	Title
2026/01/21 22:02	upstream	cf38b2340c0e	8fc37797	.config	console log	report			info	[disk image] [vmlinux] [kernel image]	ci2-upstream-kcsan-gce	KCSAN: data-race in loop_assign_backing_file / shmem_write_begin

Crashes (1):

Assets (help?)