syzbot

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BUG: KCSAN: data-race in atime_needs_update / touch_atime

read to 0xffff88810a855548 of 4 bytes by task 4506 on cpu 0:
 atime_needs_update+0x25f/0x3e0 fs/inode.c:-1
 touch_atime+0x4a/0x330 fs/inode.c:2253
 file_accessed include/linux/fs.h:2263 [inline]
 shmem_file_read_iter+0x477/0x540 mm/shmem.c:3482
 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

write to 0xffff88810a855548 of 4 bytes by task 36 on cpu 1:
 inode_set_atime_to_ts include/linux/fs.h:1625 [inline]
 inode_update_atime fs/inode.c:2104 [inline]
 inode_update_time fs/inode.c:2162 [inline]
 generic_update_time fs/inode.c:2195 [inline]
 touch_atime+0x1d7/0x330 fs/inode.c:2273
 file_accessed include/linux/fs.h:2263 [inline]
 shmem_file_read_iter+0x477/0x540 mm/shmem.c:3482
 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_rootcg_workfn+0x22/0x30 drivers/block/loop.c:1991
 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

value changed: 0x01fce672 -> 0x029592aa

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 36 Comm: kworker/u8:2 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: loop2 loop_rootcg_workfn
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