Hi Jean,
On Fri, Jun 27, 2014 at 03:57:46PM +0100, Jean Pihet wrote:
As done on other architectures (ARM64, x86, Sparc etc.).
This prevents a deadlock on down_read in do_page_fault when unwinding using fp and triggering on kernel tracepoints:
So is this an issue because you could try setting tracepoints on the pagefault path? If so, the patch is a little brutal as it would break user backtracing as soon as we take any old page fault, no?
Or am I missing something obvious?
Will
INFO: task stress:2116 blocked for more than 120 seconds. Not tainted 3.15.0-rc4-00364-g3401dfb-dirty #43 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. stress D c04b41e8 0 2116 2115 0x00000000 [<c04b41e8>] (__schedule) from [<c04b46dc>] (schedule+0x40/0x90) [<c04b46dc>] (schedule) from [<c04b6ec8>] (__down_read+0xc4/0xfc) [<c04b6ec8>] (__down_read) from [<c04b69c0>] (down_read+0x18/0x1c) [<c04b69c0>] (down_read) from [<c001d41c>] (do_page_fault+0xac/0x420) [<c001d41c>] (do_page_fault) from [<c0008444>] (do_DataAbort+0x44/0xa8) [<c0008444>] (do_DataAbort) from [<c00136b8>] (__dabt_svc+0x38/0x60) Exception stack(0xecbc3af8 to 0xecbc3b40) 3ae0: ecbc3b74 b6d72ff4 3b00: ffffffec 00000000 b6d72ff4 ec0fc000 00000000 ec0fc000 0000007e 00000000 3b20: ecbc2000 ecbc3bac 00000014 ecbc3b44 c0019e78 c021ef44 00000013 ffffffff [<c00136b8>] (__dabt_svc) from [<c021ef44>] (__copy_from_user+0xa4/0x3a0)
Signed-off-by: Jean Pihet jean.pihet@linaro.org Cc: Will Deacon will.deacon@arm.com
arch/arm/kernel/perf_event.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c index 6493c4c..f5aeca2 100644 --- a/arch/arm/kernel/perf_event.c +++ b/arch/arm/kernel/perf_event.c @@ -560,11 +560,16 @@ user_backtrace(struct frame_tail __user *tail, struct perf_callchain_entry *entry) { struct frame_tail buftail;
- unsigned long err;
- /* Also check accessibility of one struct frame_tail beyond */ if (!access_ok(VERIFY_READ, tail, sizeof(buftail))) return NULL;
- if (__copy_from_user_inatomic(&buftail, tail, sizeof(buftail)))
- pagefault_disable();
- err = __copy_from_user_inatomic(&buftail, tail, sizeof(buftail));
- pagefault_enable();
- if (err) return NULL;
perf_callchain_store(entry, buftail.lr); -- 1.8.1.2