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SubjectFwd: Potential data race in psmouse_interrupt
From
Hi!

We are working on a dynamic data race detector for Linux kernel called
KernelThreadSanitizer (ktsan) (https://github.com/google/ktsan/wiki).

Here is a report we got while running ktsan (upstream revision
21bdb584af8cca7c6df3c44cba268be050a234eb).

==================================================================
ThreadSanitizer: data-race in psmouse_interrupt

Write of size 1 by thread T1 (K1):
[<ffffffff819d5272>] psmouse_interrupt+0xd2/0x690
drivers/input/mouse/psmouse-base.c:337
[<ffffffff819bcd16>] serio_interrupt+0x66/0xb0 drivers/input/serio/serio.c:1008
[<ffffffff819be5f0>] i8042_interrupt+0x240/0x4d0
drivers/input/serio/i8042.c:541
[<ffffffff810f03b2>] handle_irq_event_percpu+0x62/0x2a0 kernel/irq/handle.c:143
[<ffffffff810f0692>] handle_irq_event+0xa2/0xf0 kernel/irq/handle.c:192
[<ffffffff810f5414>] handle_edge_irq+0x104/0x380 kernel/irq/chip.c:608
[< inlined >] handle_irq+0xf6/0x220 generic_handle_irq_desc
include/linux/irqdesc.h:146
[<ffffffff81009f86>] handle_irq+0xf6/0x220 arch/x86/kernel/irq_64.c:81
[<ffffffff810093ce>] do_IRQ+0x5e/0x110 arch/x86/kernel/irq.c:223
[<ffffffff81e726ab>] ret_from_intr+0x0/0x1f arch/x86/entry/entry_64.S:601
[< inlined >] irq_exit+0x98/0xa0 invoke_softirq kernel/softirq.c:350
[<ffffffff8108edd8>] irq_exit+0x98/0xa0 kernel/softirq.c:391
[< inlined >] smp_apic_timer_interrupt+0x63/0x80 exiting_irq
./arch/x86/include/asm/apic.h:655
[<ffffffff8105c503>] smp_apic_timer_interrupt+0x63/0x80
arch/x86/kernel/apic/apic.c:915
[<ffffffff81e7299b>] apic_timer_interrupt+0x6b/0x70
arch/x86/entry/entry_64.S:782
[<ffffffff8153223d>] kvasprintf+0x5d/0x90 lib/kasprintf.c:24
[<ffffffff815322be>] kasprintf+0x4e/0x70 lib/kasprintf.c:40
[< inlined >] module_add_driver+0x8f/0x180 make_driver_name
drivers/base/module.c:18
[<ffffffff8183059f>] module_add_driver+0x8f/0x180 drivers/base/module.c:63
[<ffffffff81812c94>] bus_add_driver+0x204/0x340 drivers/base/bus.c:713
[<ffffffff81814e2b>] driver_register+0xdb/0x190 drivers/base/driver.c:168
[<ffffffff81a5ed16>] __hid_register_driver+0xb6/0x100
drivers/hid/hid-core.c:2677
[<ffffffff825ab67d>] apple_driver_init+0x24/0x31 drivers/hid/hid-apple.c:574
[<ffffffff81000339>] do_one_initcall+0xb9/0x220 init/main.c:798
[< inlined >] kernel_init_freeable+0x2ca/0x397
do_initcall_level init/main.c:863
[< inlined >] kernel_init_freeable+0x2ca/0x397 do_initcalls
init/main.c:871
[< inlined >] kernel_init_freeable+0x2ca/0x397 do_basic_setup
init/main.c:890
[<ffffffff8253d919>] kernel_init_freeable+0x2ca/0x397 init/main.c:1013
[<ffffffff81e5ad66>] kernel_init+0x16/0x140 init/main.c:941
[<ffffffff81e71f5f>] ret_from_fork+0x3f/0x70 arch/x86/entry/entry_64.S:526
DBG: cpu = ffff88053fd9fe68
DBG: cpu id = 3

Previous read of size 1 by thread T509 (K506):
[< inlined >] cypress_send_ext_cmd+0x193/0x500
cypress_ps2_read_cmd_status drivers/input/mouse/cypress_ps2.c:123
[<ffffffff819e6b23>] cypress_send_ext_cmd+0x193/0x500
drivers/input/mouse/cypress_ps2.c:192
[<ffffffff819e6f5a>] cypress_detect+0x2a/0xb0
drivers/input/mouse/cypress_ps2.c:208
[<ffffffff819d5e66>] psmouse_extensions+0x1f6/0x4e0
drivers/input/mouse/psmouse-base.c:849 (discriminator 1)
[<ffffffff819d63fd>] psmouse_switch_protocol+0x2ad/0x330
drivers/input/mouse/psmouse-base.c:1467
[<ffffffff819d7426>] psmouse_connect+0x2e6/0x450
drivers/input/mouse/psmouse-base.c:1554 (discriminator 4)
[< inlined >] serio_driver_probe+0x57/0x80
serio_connect_driver drivers/input/serio/serio.c:65
[<ffffffff819bcf77>] serio_driver_probe+0x57/0x80
drivers/input/serio/serio.c:796
[< inlined >] driver_probe_device+0x1da/0x460 really_probe
drivers/base/dd.c:308
[<ffffffff81813b1a>] driver_probe_device+0x1da/0x460 drivers/base/dd.c:414
[<ffffffff81813e64>] __driver_attach+0xc4/0xd0 drivers/base/dd.c:612
[<ffffffff81810933>] bus_for_each_dev+0x93/0xe0 drivers/base/bus.c:314
[<ffffffff81813353>] driver_attach+0x33/0x50 drivers/base/dd.c:631
[< inlined >] serio_handle_event+0x2d3/0x3b0
serio_attach_driver drivers/input/serio/serio.c:826
[<ffffffff819bd8e3>] serio_handle_event+0x2d3/0x3b0
drivers/input/serio/serio.c:245
[<ffffffff810adcf9>] process_one_work+0x2a9/0x6d0 kernel/workqueue.c:2036
[<ffffffff810aeddf>] worker_thread+0xbf/0x710 kernel/workqueue.c:2170
[<ffffffff810b700c>] kthread+0x15c/0x180 kernel/kthread.c:207
[<ffffffff81e71f5f>] ret_from_fork+0x3f/0x70 arch/x86/entry/entry_64.S:526
DBG: cpu = 0

DBG: addr: ffff88019d703909
DBG: first offset: 1, second offset: 1
DBG: T1 clock: {T1: 17075020, T509: 142163}
DBG: T509 clock: {T509: 142167}
==================================================================

It seems that accessing 'psmouse->pktcnt' in
'psmouse->packet[psmouse->pktcnt++] = data' in 'psmouse_interrupt()'
is racing with 'wait_event_timeout(ps2dev->wait, (psmouse->pktcnt >=
pktsize), msecs_to_jiffies(CYTP_CMD_TIMEOUT))' in
'cypress_ps2_read_cmd_status()'.
If that's the case, it's possible that 'psmouse->pktcnt' is
incremented, but no data is written yet, so '(psmouse->pktcnt >=
pktsize)' will evaluate to true and the following 'memcpy' will access
invalid data.

Could you confirm if this is a real data race?

Thanks in advance!


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