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SubjectRe: [PATCH] char/random: fix data races at timer_rand_state
On Tue, Feb 25, 2020 at 11:27:04AM -0500, Qian Cai wrote:
> Fields in "struct timer_rand_state" could be accessed concurrently.
> Lockless plain reads and writes result in data races. Fix them by adding
> pairs of READ|WRITE_ONCE(). The data races were reported by KCSAN,
>
> BUG: KCSAN: data-race in add_timer_randomness / add_timer_randomness
>
> write to 0xffff9f320a0a01d0 of 8 bytes by interrupt on cpu 22:
> add_timer_randomness+0x100/0x190
> add_timer_randomness at drivers/char/random.c:1152
> add_disk_randomness+0x85/0x280
> scsi_end_request+0x43a/0x4a0
> scsi_io_completion+0xb7/0x7e0
> scsi_finish_command+0x1ed/0x2a0
> scsi_softirq_done+0x1c9/0x1d0
> blk_done_softirq+0x181/0x1d0
> __do_softirq+0xd9/0x57c
> irq_exit+0xa2/0xc0
> do_IRQ+0x8b/0x190
> ret_from_intr+0x0/0x42
> cpuidle_enter_state+0x15e/0x980
> cpuidle_enter+0x69/0xc0
> call_cpuidle+0x23/0x40
> do_idle+0x248/0x280
> cpu_startup_entry+0x1d/0x1f
> start_secondary+0x1b2/0x230
> secondary_startup_64+0xb6/0xc0
>
> no locks held by swapper/22/0.
> irq event stamp: 32871382
> _raw_spin_unlock_irqrestore+0x53/0x60
> _raw_spin_lock_irqsave+0x21/0x60
> _local_bh_enable+0x21/0x30
> irq_exit+0xa2/0xc0
>
> read to 0xffff9f320a0a01d0 of 8 bytes by interrupt on cpu 2:
> add_timer_randomness+0xe8/0x190
> add_disk_randomness+0x85/0x280
> scsi_end_request+0x43a/0x4a0
> scsi_io_completion+0xb7/0x7e0
> scsi_finish_command+0x1ed/0x2a0
> scsi_softirq_done+0x1c9/0x1d0
> blk_done_softirq+0x181/0x1d0
> __do_softirq+0xd9/0x57c
> irq_exit+0xa2/0xc0
> do_IRQ+0x8b/0x190
> ret_from_intr+0x0/0x42
> cpuidle_enter_state+0x15e/0x980
> cpuidle_enter+0x69/0xc0
> call_cpuidle+0x23/0x40
> do_idle+0x248/0x280
> cpu_startup_entry+0x1d/0x1f
> start_secondary+0x1b2/0x230
> secondary_startup_64+0xb6/0xc0
>
> no locks held by swapper/2/0.
> irq event stamp: 37846304
> _raw_spin_unlock_irqrestore+0x53/0x60
> _raw_spin_lock_irqsave+0x21/0x60
> _local_bh_enable+0x21/0x30
> irq_exit+0xa2/0xc0
>
> Reported by Kernel Concurrency Sanitizer on:
> Hardware name: HP ProLiant BL660c Gen9, BIOS I38 10/17/2018
>
> Signed-off-by: Qian Cai <cai@lca.pw>

Thanks, applied.

- Ted

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