linux-kernel - Re: [PATCH] char/random: fix data races at timer_rand

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Date:   Thu, 27 Feb 2020 23:11:14 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Qian Cai <cai@....pw>
Cc:     elver@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [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@....pw>

Thanks, applied.

					- Ted