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Message-Id: <1312059200-11563-1-git-send-email-dsahern@gmail.com>
Date: Sat, 30 Jul 2011 14:53:20 -0600
From: David Ahern <dsahern@...il.com>
To: benh@...nel.crashing.org, anton@...ba.org
Cc: acme@...stprotocols.net, mingo@...e.hu, peterz@...radead.org,
paulus@...ba.org, linuxppc-dev@...ts.ozlabs.org,
linux-kernel@...r.kernel.org, David Ahern <dsahern@...il.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: [PATCH] perf: powerpc: Disable pagefaults during callchain stack read
Panic observed on an older kernel when collecting call chains for
the context-switch software event:
[<b0180e00>]rb_erase+0x1b4/0x3e8
[<b00430f4>]__dequeue_entity+0x50/0xe8
[<b0043304>]set_next_entity+0x178/0x1bc
[<b0043440>]pick_next_task_fair+0xb0/0x118
[<b02ada80>]schedule+0x500/0x614
[<b02afaa8>]rwsem_down_failed_common+0xf0/0x264
[<b02afca0>]rwsem_down_read_failed+0x34/0x54
[<b02aed4c>]down_read+0x3c/0x54
[<b0023b58>]do_page_fault+0x114/0x5e8
[<b001e350>]handle_page_fault+0xc/0x80
[<b0022dec>]perf_callchain+0x224/0x31c
[<b009ba70>]perf_prepare_sample+0x240/0x2fc
[<b009d760>]__perf_event_overflow+0x280/0x398
[<b009d914>]perf_swevent_overflow+0x9c/0x10c
[<b009db54>]perf_swevent_ctx_event+0x1d0/0x230
[<b009dc38>]do_perf_sw_event+0x84/0xe4
[<b009dde8>]perf_sw_event_context_switch+0x150/0x1b4
[<b009de90>]perf_event_task_sched_out+0x44/0x2d4
[<b02ad840>]schedule+0x2c0/0x614
[<b0047dc0>]__cond_resched+0x34/0x90
[<b02adcc8>]_cond_resched+0x4c/0x68
[<b00bccf8>]move_page_tables+0xb0/0x418
[<b00d7ee0>]setup_arg_pages+0x184/0x2a0
[<b0110914>]load_elf_binary+0x394/0x1208
[<b00d6e28>]search_binary_handler+0xe0/0x2c4
[<b00d834c>]do_execve+0x1bc/0x268
[<b0015394>]sys_execve+0x84/0xc8
[<b001df10>]ret_from_syscall+0x0/0x3c
A page fault occurred walking the callchain while creating a perf
sample for the context-switch event. To handle the page fault the
mmap_sem is needed, but it is currently held by setup_arg_pages.
(setup_arg_pages calls shift_arg_pages with the mmap_sem held.
shift_arg_pages then calls move_page_tables which has a cond_resched
at the top of its for loop - hitting that cond_resched is what caused
the context switch.)
This is an extension of Anton's proposed patch:
https://lkml.org/lkml/2011/7/24/151
adding case for 32-bit ppc.
Tested on the system that first generated the panic and then again
with latest kernel using a PPC VM. I am not able to test the 64-bit
path - I do not have H/W for it and 64-bit PPC VMs (qemu on Intel)
is horribly slow.
Signed-off-by: David Ahern <dsahern@...il.com>
CC: Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC: Anton Blanchard <anton@...ba.org>
CC: Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC: Paul Mackerras <paulus@...ba.org>
CC: Ingo Molnar <mingo@...e.hu>
CC: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC: linuxppc-dev@...ts.ozlabs.org
CC: linux-kernel@...r.kernel.org
---
arch/powerpc/kernel/perf_callchain.c | 20 +++++++++++++++++---
1 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/kernel/perf_callchain.c b/arch/powerpc/kernel/perf_callchain.c
index d05ae42..564c1d8 100644
--- a/arch/powerpc/kernel/perf_callchain.c
+++ b/arch/powerpc/kernel/perf_callchain.c
@@ -154,8 +154,12 @@ static int read_user_stack_64(unsigned long __user *ptr, unsigned long *ret)
((unsigned long)ptr & 7))
return -EFAULT;
- if (!__get_user_inatomic(*ret, ptr))
+ pagefault_disable();
+ if (!__get_user_inatomic(*ret, ptr)) {
+ pagefault_enable();
return 0;
+ }
+ pagefault_enable();
return read_user_stack_slow(ptr, ret, 8);
}
@@ -166,8 +170,12 @@ static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
((unsigned long)ptr & 3))
return -EFAULT;
- if (!__get_user_inatomic(*ret, ptr))
+ pagefault_disable();
+ if (!__get_user_inatomic(*ret, ptr)) {
+ pagefault_enable();
return 0;
+ }
+ pagefault_enable();
return read_user_stack_slow(ptr, ret, 4);
}
@@ -294,11 +302,17 @@ static inline int current_is_64bit(void)
*/
static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
{
+ int rc;
+
if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
((unsigned long)ptr & 3))
return -EFAULT;
- return __get_user_inatomic(*ret, ptr);
+ pagefault_disable();
+ rc = __get_user_inatomic(*ret, ptr);
+ pagefault_enable();
+
+ return rc;
}
static inline void perf_callchain_user_64(struct perf_callchain_entry *entry,
--
1.7.6
--
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