| From 6772faa1ba22eba18d087c2459030a683b65be57 Mon Sep 17 00:00:00 2001 |
| From: Michael Ellerman <michael@ellerman.id.au> |
| Date: Wed, 5 Jun 2013 17:58:20 +0000 |
| Subject: powerpc/perf: Fix deadlock caused by calling printk() in PMU exception |
| |
| From: Michael Ellerman <michael@ellerman.id.au> |
| |
| commit 6772faa1ba22eba18d087c2459030a683b65be57 upstream. |
| |
| In commit bc09c21 "Fix finding overflowed PMC in interrupt" we added |
| a printk() to the PMU exception handler. Unfortunately that is not safe. |
| |
| The problem is that the PMU exception may run even when interrupts are |
| soft disabled, aka NMI context. We do this so that we can profile parts |
| of the kernel that have interrupts soft-disabled. |
| |
| But by calling printk() from the exception handler, we can potentially |
| deadlock in the printk code on logbuf_lock, eg: |
| |
| [c00000038ba575c0] c000000000081928 .vprintk_emit+0xa8/0x540 |
| [c00000038ba576a0] c0000000007bcde8 .printk+0x48/0x58 |
| [c00000038ba57710] c000000000076504 .perf_event_interrupt+0x2d4/0x490 |
| [c00000038ba57810] c00000000001f6f8 .performance_monitor_exception+0x48/0x60 |
| [c00000038ba57880] c0000000000032cc performance_monitor_common+0x14c/0x180 |
| --- Exception: f01 (Performance Monitor) at c0000000007b25d4 ._raw_spin_lock_irq |
| +0x64/0xc0 |
| [c00000038ba57bf0] c00000000007ed90 .devkmsg_read+0xd0/0x5a0 |
| [c00000038ba57d00] c0000000001c2934 .vfs_read+0xc4/0x1e0 |
| [c00000038ba57d90] c0000000001c2cd8 .SyS_read+0x58/0xd0 |
| [c00000038ba57e30] c000000000009d54 syscall_exit+0x0/0x98 |
| --- Exception: c01 (System Call) at 00001fffffbf6f7c |
| SP (3ffff6d4de10) is in userspace |
| |
| Fix it by making sure we only call printk() when we are not in NMI |
| context. |
| |
| Signed-off-by: Michael Ellerman <michael@ellerman.id.au> |
| Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| arch/powerpc/perf/core-book3s.c | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- a/arch/powerpc/perf/core-book3s.c |
| +++ b/arch/powerpc/perf/core-book3s.c |
| @@ -1528,7 +1528,7 @@ static void perf_event_interrupt(struct |
| } |
| } |
| } |
| - if ((!found) && printk_ratelimit()) |
| + if (!found && !nmi && printk_ratelimit()) |
| printk(KERN_WARNING "Can't find PMC that caused IRQ\n"); |
| |
| /* |
