Messages in this thread | | | Subject | Re: cpu softplug kernel hang | From | Suresh Siddha <> | Date | Thu, 08 Jul 2010 15:17:46 -0700 |
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On Thu, 2010-07-08 at 11:52 -0700, Prarit Bhargava wrote: > The panic below is from an 2.6.32-based kernel, however, AFAICT the same > issue exists with the latest 2.6.35-rc3+ kernel. > > I have diagnosed the issue as being identical to the issue that I fixed > with the Intel rngd > driver sometime ago: > > http://marc.info/?l=linux-kernel&m=117275119001289&w=2 > > When doing the following, > > while true; do > for i in `seq 12 23`; do echo 0 > > /sys/devices/system/cpu/cpu$i/online; done > sleep 5 > for i in `seq 12 23`; do echo 1 > > /sys/devices/system/cpu/cpu$i/online; done > sleep 5 > done > > I see (with the nmi_watchdog enabled) > > BUG: NMI Watchdog detected LOCKUP on CPU11, ip ffffffff81029e72, registers: > CPU 11 > Modules linked in: nfs lockd fscache nfs_acl auth_rpcgss autofs4 sunrpc > cpufreq_ondemand acpi_cpufreq freq_table ipv6 dm_mirror dm_region_hash dm_log > uinput sg serio_raw i2c_i801 iTCO_wdt iTCO_vendor_support ioatdma i7core_edac > edac_core shpchp igb dca ext4 mbcache jbd2 sr_mod cdrom sd_mod crc_t10dif ahci > pata_acpi ata_generic pata_jmicron radeon ttm drm_kms_helper drm i2c_algo_bit > i2c_core dm_mod [last unloaded: microcode] > > Modules linked in: nfs lockd fscache nfs_acl auth_rpcgss autofs4 sunrpc > cpufreq_ondemand acpi_cpufreq freq_table ipv6 dm_mirror dm_region_hash dm_log > uinput sg serio_raw i2c_i801 iTCO_wdt iTCO_vendor_support ioatdma i7core_edac > edac_core shpchp igb dca ext4 mbcache jbd2 sr_mod cdrom sd_mod crc_t10dif ahci > pata_acpi ata_generic pata_jmicron radeon ttm drm_kms_helper drm i2c_algo_bit > i2c_core dm_mod [last unloaded: microcode] > Pid: 704, comm: kexec Not tainted 2.6.32 #1 X8DTN > RIP: 0010:[<ffffffff81029e72>] [<ffffffff81029e72>] ipi_handler+0x32/0xa0 > RSP: 0000:ffff8801474a3f58 EFLAGS: 00000046 > RAX: 0000000000000000 RBX: ffff880337393ea8 RCX: ffff88013ae41580 > RDX: 00000000ffffffff RSI: 0000000000000000 RDI: ffff880337393ea8 > RBP: ffff8801474a3f68 R08: 0000000061c941a6 R09: 00000000578070b9 > R10: 0000000080507210 R11: 0000000025410601 R12: 0000000000000086 > R13: 00000000ffffffff R14: ffffffff817491d0 R15: 0000000090793245 > FS: 00007fefd5f3d700(0000) GS:ffff8801474a0000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b > CR2: 000000000040d000 CR3: 0000000316a8e000 CR4: 00000000000006e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > Process kexec (pid: 704, threadinfo ffff880314caa000, task ffff880335a0b500) > Stack: > ffff880147571f40 000000000000000b ffff8801474a3f98 ffffffff810a6d28 > <0> 00000000aa149910 00000000f21570f0 000000000008b495 00000000521ebd53 > <0> ffff8801474a3fa8 ffffffff8102ea57 ffff880314cabf80 ffffffff81013e53 > Call Trace: > <IRQ> > [<ffffffff810a6d28>] generic_smp_call_function_interrupt+0x78/0x130 > [<ffffffff8102ea57>] smp_call_function_interrupt+0x27/0x40 > [<ffffffff81013e53>] call_function_interrupt+0x13/0x20 > <EOI> > Code: 0f 1f 44 00 00 48 89 fb 9c 58 0f 1f 44 00 00 49 89 c4 fa 66 0f 1f 44 00 > 00 f0 ff 0f 8b 47 04 85 c0 75 0f 66 0f 1f 44 00 00 f3 90 <8b> 43 04 85 c0 74 f7 > 8b 7b 18 83 ff ff 74 47 48 8b 05 08 25 a1 > > Since this is a panic, I get traces from all other cpus. > > CPU 14 is in _write_lock_irq > CPU 2 is in _read_lock
which is this lock?
> CPU 6 has called smp_call_function() with the ipi_handler to sync mtrr's on > the new cpu
Either we need to take that lock at all the places with interrupts disabled or we need to implement the rendezvous logic using stop machine.
thanks, suresh > > The problem is that ipi_handler does this: > > static void ipi_handler(void *info) > { > #ifdef CONFIG_SMP > struct set_mtrr_data *data = info; > unsigned long flags; > > local_irq_save(flags); > > atomic_dec(&data->count); << global value that each processor entering > ipi_handler decrements > while (!atomic_read(&data->gate)) << 1 when data->count != 0 > cpu_relax(); > > So what happens is that CPU 2 is in _read_lock and has acquired a lock. CPU 14 > is waiting for the release of that lock with IRQs *off*. > > CPU 6 launches smp_call_function, and CPU 2 answers and runs the ipi_handler() > and waits (as do all other processors). > > CPU 14, however, does not see the IPI because it is waiting with interrupts off > for the lock that CPU 2 is holding. > > Boom. Deadlock. > > I'm planning on fixing this by rewriting this code and using stop_machine_run() > to synchronize the cpus instead of doing it in the ipi_handler. > > Unless, of course, someone has a better suggestion. > > P. > > > >
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