syzbot

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BUG: KCSAN: data-race in atime_needs_update / touch_atime

read to 0xffff88811be1d3f8 of 4 bytes by task 91 on cpu 0:
 atime_needs_update+0x25f/0x3e0 fs/inode.c:-1
 touch_atime+0x4a/0x300 fs/inode.c:2315
 file_accessed include/linux/fs.h:2277 [inline]
 shmem_file_read_iter+0x3ed/0x4b0 mm/shmem.c:3394
 lo_rw_aio+0x6a9/0x760 drivers/block/loop.c:-1
 do_req_filebacked drivers/block/loop.c:-1 [inline]
 loop_handle_cmd drivers/block/loop.c:1921 [inline]
 loop_process_work+0x567/0xac0 drivers/block/loop.c:1956
 loop_rootcg_workfn+0x22/0x30 drivers/block/loop.c:1987
 process_one_work kernel/workqueue.c:3322 [inline]
 process_scheduled_works+0x4d4/0x9a0 kernel/workqueue.c:3405
 worker_thread+0x569/0x750 kernel/workqueue.c:3486
 kthread+0x221/0x270 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

write to 0xffff88811be1d3f8 of 4 bytes by task 362 on cpu 1:
 inode_set_atime_to_ts include/linux/fs.h:1626 [inline]
 inode_update_atime fs/inode.c:2160 [inline]
 inode_update_time fs/inode.c:2224 [inline]
 generic_update_time fs/inode.c:2257 [inline]
 touch_atime+0x1cb/0x300 fs/inode.c:2335
 file_accessed include/linux/fs.h:2277 [inline]
 shmem_file_read_iter+0x3ed/0x4b0 mm/shmem.c:3394
 lo_rw_aio+0x6a9/0x760 drivers/block/loop.c:-1
 do_req_filebacked drivers/block/loop.c:-1 [inline]
 loop_handle_cmd drivers/block/loop.c:1921 [inline]
 loop_process_work+0x567/0xac0 drivers/block/loop.c:1956
 loop_workfn+0x31/0x40 drivers/block/loop.c:1980
 process_one_work kernel/workqueue.c:3322 [inline]
 process_scheduled_works+0x4d4/0x9a0 kernel/workqueue.c:3405
 worker_thread+0x569/0x750 kernel/workqueue.c:3486
 kthread+0x221/0x270 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x12e15564 -> 0x134d623e

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 362 Comm: kworker/u8:6 Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: loop5 loop_workfn
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