From mboxrd@z Thu Jan 1 00:00:00 1970 From: jean.pihet@linaro.org (Jean Pihet) Date: Fri, 27 Jun 2014 16:57:46 +0200 Subject: [PATCH 2/3] ARM: perf: disable the pagefault handler when reading from user space In-Reply-To: <1403881067-22690-1-git-send-email-jean.pihet@linaro.org> References: <1403881067-22690-1-git-send-email-jean.pihet@linaro.org> Message-ID: <1403881067-22690-3-git-send-email-jean.pihet@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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: 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 [] (__schedule) from [] (schedule+0x40/0x90) [] (schedule) from [] (__down_read+0xc4/0xfc) [] (__down_read) from [] (down_read+0x18/0x1c) [] (down_read) from [] (do_page_fault+0xac/0x420) [] (do_page_fault) from [] (do_DataAbort+0x44/0xa8) [] (do_DataAbort) from [] (__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 [] (__dabt_svc) from [] (__copy_from_user+0xa4/0x3a0) Signed-off-by: Jean Pihet Cc: Will Deacon --- 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