From: "Gautham R. Shenoy" ego@linux.vnet.ibm.com

xive_find_target_in_mask() has the following for(;;) loop which has a bug when @first == cpumask_first(@mask) and condition 1 fails to hold for every CPU in @mask. In this case we loop forever in the for-loop.

first = cpu; for (;;) { if (cpu_online(cpu) && xive_try_pick_target(cpu)) // condition 1 return cpu; cpu = cpumask_next(cpu, mask); if (cpu == first) // condition 2 break;

if (cpu >= nr_cpu_ids) // condition 3 cpu = cpumask_first(mask); }

This is because, when @first == cpumask_first(@mask), we never hit the condition 2 (cpu == first) since prior to this check, we would have executed "cpu = cpumask_next(cpu, mask)" which will set the value of @cpu to a value greater than @first or to nr_cpus_ids. When this is coupled with the fact that condition 1 is not met, we will never exit this loop.

This was discovered by the hard-lockup detector while running LTP test concurrently with SMT switch tests.

watchdog: CPU 12 detected hard LOCKUP on other CPUs 68 watchdog: CPU 12 TB:85587019220796, last SMP heartbeat TB:85578827223399 (15999ms ago) watchdog: CPU 68 Hard LOCKUP watchdog: CPU 68 TB:85587019361273, last heartbeat TB:85576815065016 (19930ms ago) CPU: 68 PID: 45050 Comm: hxediag Kdump: loaded Not tainted 4.18.0-100.el8.ppc64le #1 NIP: c0000000006f5578 LR: c000000000cba9ec CTR: 0000000000000000 REGS: c000201fff3c7d80 TRAP: 0100 Not tainted (4.18.0-100.el8.ppc64le) MSR: 9000000002883033 <SF,HV,VEC,VSX,FP,ME,IR,DR,RI,LE> CR: 24028424 XER: 00000000 CFAR: c0000000006f558c IRQMASK: 1 GPR00: c0000000000afc58 c000201c01c43400 c0000000015ce500 c000201cae26ec18 GPR04: 0000000000000800 0000000000000540 0000000000000800 00000000000000f8 GPR08: 0000000000000020 00000000000000a8 0000000080000000 c00800001a1beed8 GPR12: c0000000000b1410 c000201fff7f4c00 0000000000000000 0000000000000000 GPR16: 0000000000000000 0000000000000000 0000000000000540 0000000000000001 GPR20: 0000000000000048 0000000010110000 c00800001a1e3780 c000201cae26ed18 GPR24: 0000000000000000 c000201cae26ed8c 0000000000000001 c000000001116bc0 GPR28: c000000001601ee8 c000000001602494 c000201cae26ec18 000000000000001f NIP [c0000000006f5578] find_next_bit+0x38/0x90 LR [c000000000cba9ec] cpumask_next+0x2c/0x50 Call Trace: [c000201c01c43400] [c000201cae26ec18] 0xc000201cae26ec18 (unreliable) [c000201c01c43420] [c0000000000afc58] xive_find_target_in_mask+0x1b8/0x240 [c000201c01c43470] [c0000000000b0228] xive_pick_irq_target.isra.3+0x168/0x1f0 [c000201c01c435c0] [c0000000000b1470] xive_irq_startup+0x60/0x260 [c000201c01c43640] [c0000000001d8328] __irq_startup+0x58/0xf0 [c000201c01c43670] [c0000000001d844c] irq_startup+0x8c/0x1a0 [c000201c01c436b0] [c0000000001d57b0] __setup_irq+0x9f0/0xa90 [c000201c01c43760] [c0000000001d5aa0] request_threaded_irq+0x140/0x220 [c000201c01c437d0] [c00800001a17b3d4] bnx2x_nic_load+0x188c/0x3040 [bnx2x] [c000201c01c43950] [c00800001a187c44] bnx2x_self_test+0x1fc/0x1f70 [bnx2x] [c000201c01c43a90] [c000000000adc748] dev_ethtool+0x11d8/0x2cb0 [c000201c01c43b60] [c000000000b0b61c] dev_ioctl+0x5ac/0xa50 [c000201c01c43bf0] [c000000000a8d4ec] sock_do_ioctl+0xbc/0x1b0 [c000201c01c43c60] [c000000000a8dfb8] sock_ioctl+0x258/0x4f0 [c000201c01c43d20] [c0000000004c9704] do_vfs_ioctl+0xd4/0xa70 [c000201c01c43de0] [c0000000004ca274] sys_ioctl+0xc4/0x160 [c000201c01c43e30] [c00000000000b388] system_call+0x5c/0x70 Instruction dump: 78aad182 54a806be 3920ffff 78a50664 794a1f24 7d294036 7d43502a 7d295039 4182001c 48000034 78a9d182 79291f24 <7d23482a> 2fa90000 409e0020 38a50040

To fix this, move the check for condition 2 after the check for condition 3, so that we are able to break out of the loop soon after iterating through all the CPUs in the @mask in the problem case. Use do..while() to achieve this.

Fixes: 243e25112d06 ("powerpc/xive: Native exploitation of the XIVE interrupt controller") Cc: stable@vger.kernel.org # 4.12+ Reported-by: Indira P. Joga indira.priya@in.ibm.com Signed-off-by: Gautham R. Shenoy ego@linux.vnet.ibm.com --- arch/powerpc/sysdev/xive/common.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/sysdev/xive/common.c b/arch/powerpc/sysdev/xive/common.c index 082c7e1..1cdb395 100644 --- a/arch/powerpc/sysdev/xive/common.c +++ b/arch/powerpc/sysdev/xive/common.c @@ -479,7 +479,7 @@ static int xive_find_target_in_mask(const struct cpumask *mask, * Now go through the entire mask until we find a valid * target. */ - for (;;) { + do { /* * We re-check online as the fallback case passes us * an untested affinity mask @@ -487,12 +487,11 @@ static int xive_find_target_in_mask(const struct cpumask *mask, if (cpu_online(cpu) && xive_try_pick_target(cpu)) return cpu; cpu = cpumask_next(cpu, mask); - if (cpu == first) - break; /* Wrap around */ if (cpu >= nr_cpu_ids) cpu = cpumask_first(mask); - } + } while (cpu != first); + return -1; }