Re: [PATCH v4 05/10] signal: Introduce TRAP_PERF si_code and si_perf to siginfo

[Marek Szyprowski]

Hi Marco,

On 08.04.2021 12:36, Marco Elver wrote:
> Introduces the TRAP_PERF si_code, and associated siginfo_t field
> si_perf. These will be used by the perf event subsystem to send signals
> (if requested) to the task where an event occurred.
>
> Acked-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> # m68k
> Acked-by: Arnd Bergmann <arnd@xxxxxxxx> # asm-generic
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>

This patch landed in linux-next as commit fb6cc127e0b6 ("signal: 
Introduce TRAP_PERF si_code and si_perf to siginfo"). It causes 
regression on my test systems (arm 32bit and 64bit). Most systems fails 
to boot in the given time frame. I've observed that there is a timeout 
waiting for udev to populate /dev and then also during the network 
interfaces configuration. Reverting this commit, together with 
97ba62b27867 ("perf: Add support for SIGTRAP on perf events") to let it 
compile, on top of next-20210420 fixes the issue.

> ---
>   arch/m68k/kernel/signal.c          |  3 +++
>   arch/x86/kernel/signal_compat.c    |  5 ++++-
>   fs/signalfd.c                      |  4 ++++
>   include/linux/compat.h             |  2 ++
>   include/linux/signal.h             |  1 +
>   include/uapi/asm-generic/siginfo.h |  6 +++++-
>   include/uapi/linux/signalfd.h      |  4 +++-
>   kernel/signal.c                    | 11 +++++++++++
>   8 files changed, 33 insertions(+), 3 deletions(-)
>
> diff --git a/arch/m68k/kernel/signal.c b/arch/m68k/kernel/signal.c
> index 349570f16a78..a4b7ee1df211 100644
> --- a/arch/m68k/kernel/signal.c
> +++ b/arch/m68k/kernel/signal.c
> @@ -622,6 +622,9 @@ static inline void siginfo_build_tests(void)
>   	/* _sigfault._addr_pkey */
>   	BUILD_BUG_ON(offsetof(siginfo_t, si_pkey) != 0x12);
>   
> +	/* _sigfault._perf */
> +	BUILD_BUG_ON(offsetof(siginfo_t, si_perf) != 0x10);
> +
>   	/* _sigpoll */
>   	BUILD_BUG_ON(offsetof(siginfo_t, si_band)   != 0x0c);
>   	BUILD_BUG_ON(offsetof(siginfo_t, si_fd)     != 0x10);
> diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
> index a5330ff498f0..0e5d0a7e203b 100644
> --- a/arch/x86/kernel/signal_compat.c
> +++ b/arch/x86/kernel/signal_compat.c
> @@ -29,7 +29,7 @@ static inline void signal_compat_build_tests(void)
>   	BUILD_BUG_ON(NSIGFPE  != 15);
>   	BUILD_BUG_ON(NSIGSEGV != 9);
>   	BUILD_BUG_ON(NSIGBUS  != 5);
> -	BUILD_BUG_ON(NSIGTRAP != 5);
> +	BUILD_BUG_ON(NSIGTRAP != 6);
>   	BUILD_BUG_ON(NSIGCHLD != 6);
>   	BUILD_BUG_ON(NSIGSYS  != 2);
>   
> @@ -138,6 +138,9 @@ static inline void signal_compat_build_tests(void)
>   	BUILD_BUG_ON(offsetof(siginfo_t, si_pkey) != 0x20);
>   	BUILD_BUG_ON(offsetof(compat_siginfo_t, si_pkey) != 0x14);
>   
> +	BUILD_BUG_ON(offsetof(siginfo_t, si_perf) != 0x18);
> +	BUILD_BUG_ON(offsetof(compat_siginfo_t, si_perf) != 0x10);
> +
>   	CHECK_CSI_OFFSET(_sigpoll);
>   	CHECK_CSI_SIZE  (_sigpoll, 2*sizeof(int));
>   	CHECK_SI_SIZE   (_sigpoll, 4*sizeof(int));
> diff --git a/fs/signalfd.c b/fs/signalfd.c
> index 456046e15873..040a1142915f 100644
> --- a/fs/signalfd.c
> +++ b/fs/signalfd.c
> @@ -134,6 +134,10 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
>   #endif
>   		new.ssi_addr_lsb = (short) kinfo->si_addr_lsb;
>   		break;
> +	case SIL_PERF_EVENT:
> +		new.ssi_addr = (long) kinfo->si_addr;
> +		new.ssi_perf = kinfo->si_perf;
> +		break;
>   	case SIL_CHLD:
>   		new.ssi_pid    = kinfo->si_pid;
>   		new.ssi_uid    = kinfo->si_uid;
> diff --git a/include/linux/compat.h b/include/linux/compat.h
> index 6e65be753603..c8821d966812 100644
> --- a/include/linux/compat.h
> +++ b/include/linux/compat.h
> @@ -236,6 +236,8 @@ typedef struct compat_siginfo {
>   					char _dummy_pkey[__COMPAT_ADDR_BND_PKEY_PAD];
>   					u32 _pkey;
>   				} _addr_pkey;
> +				/* used when si_code=TRAP_PERF */
> +				compat_u64 _perf;
>   			};
>   		} _sigfault;
>   
> diff --git a/include/linux/signal.h b/include/linux/signal.h
> index 205526c4003a..1e98548d7cf6 100644
> --- a/include/linux/signal.h
> +++ b/include/linux/signal.h
> @@ -43,6 +43,7 @@ enum siginfo_layout {
>   	SIL_FAULT_MCEERR,
>   	SIL_FAULT_BNDERR,
>   	SIL_FAULT_PKUERR,
> +	SIL_PERF_EVENT,
>   	SIL_CHLD,
>   	SIL_RT,
>   	SIL_SYS,
> diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
> index d2597000407a..d0bb9125c853 100644
> --- a/include/uapi/asm-generic/siginfo.h
> +++ b/include/uapi/asm-generic/siginfo.h
> @@ -91,6 +91,8 @@ union __sifields {
>   				char _dummy_pkey[__ADDR_BND_PKEY_PAD];
>   				__u32 _pkey;
>   			} _addr_pkey;
> +			/* used when si_code=TRAP_PERF */
> +			__u64 _perf;
>   		};
>   	} _sigfault;
>   
> @@ -155,6 +157,7 @@ typedef struct siginfo {
>   #define si_lower	_sifields._sigfault._addr_bnd._lower
>   #define si_upper	_sifields._sigfault._addr_bnd._upper
>   #define si_pkey		_sifields._sigfault._addr_pkey._pkey
> +#define si_perf		_sifields._sigfault._perf
>   #define si_band		_sifields._sigpoll._band
>   #define si_fd		_sifields._sigpoll._fd
>   #define si_call_addr	_sifields._sigsys._call_addr
> @@ -253,7 +256,8 @@ typedef struct siginfo {
>   #define TRAP_BRANCH     3	/* process taken branch trap */
>   #define TRAP_HWBKPT     4	/* hardware breakpoint/watchpoint */
>   #define TRAP_UNK	5	/* undiagnosed trap */
> -#define NSIGTRAP	5
> +#define TRAP_PERF	6	/* perf event with sigtrap=1 */
> +#define NSIGTRAP	6
>   
>   /*
>    * There is an additional set of SIGTRAP si_codes used by ptrace
> diff --git a/include/uapi/linux/signalfd.h b/include/uapi/linux/signalfd.h
> index 83429a05b698..7e333042c7e3 100644
> --- a/include/uapi/linux/signalfd.h
> +++ b/include/uapi/linux/signalfd.h
> @@ -39,6 +39,8 @@ struct signalfd_siginfo {
>   	__s32 ssi_syscall;
>   	__u64 ssi_call_addr;
>   	__u32 ssi_arch;
> +	__u32 __pad3;
> +	__u64 ssi_perf;
>   
>   	/*
>   	 * Pad strcture to 128 bytes. Remember to update the
> @@ -49,7 +51,7 @@ struct signalfd_siginfo {
>   	 * comes out of a read(2) and we really don't want to have
>   	 * a compat on read(2).
>   	 */
> -	__u8 __pad[28];
> +	__u8 __pad[16];
>   };
>   
>   
> diff --git a/kernel/signal.c b/kernel/signal.c
> index f2718350bf4b..7061e4957650 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1199,6 +1199,7 @@ static inline bool has_si_pid_and_uid(struct kernel_siginfo *info)
>   	case SIL_FAULT_MCEERR:
>   	case SIL_FAULT_BNDERR:
>   	case SIL_FAULT_PKUERR:
> +	case SIL_PERF_EVENT:
>   	case SIL_SYS:
>   		ret = false;
>   		break;
> @@ -2531,6 +2532,7 @@ static void hide_si_addr_tag_bits(struct ksignal *ksig)
>   	case SIL_FAULT_MCEERR:
>   	case SIL_FAULT_BNDERR:
>   	case SIL_FAULT_PKUERR:
> +	case SIL_PERF_EVENT:
>   		ksig->info.si_addr = arch_untagged_si_addr(
>   			ksig->info.si_addr, ksig->sig, ksig->info.si_code);
>   		break;
> @@ -3341,6 +3343,10 @@ void copy_siginfo_to_external32(struct compat_siginfo *to,
>   #endif
>   		to->si_pkey = from->si_pkey;
>   		break;
> +	case SIL_PERF_EVENT:
> +		to->si_addr = ptr_to_compat(from->si_addr);
> +		to->si_perf = from->si_perf;
> +		break;
>   	case SIL_CHLD:
>   		to->si_pid = from->si_pid;
>   		to->si_uid = from->si_uid;
> @@ -3421,6 +3427,10 @@ static int post_copy_siginfo_from_user32(kernel_siginfo_t *to,
>   #endif
>   		to->si_pkey = from->si_pkey;
>   		break;
> +	case SIL_PERF_EVENT:
> +		to->si_addr = compat_ptr(from->si_addr);
> +		to->si_perf = from->si_perf;
> +		break;
>   	case SIL_CHLD:
>   		to->si_pid    = from->si_pid;
>   		to->si_uid    = from->si_uid;
> @@ -4601,6 +4611,7 @@ static inline void siginfo_buildtime_checks(void)
>   	CHECK_OFFSET(si_lower);
>   	CHECK_OFFSET(si_upper);
>   	CHECK_OFFSET(si_pkey);
> +	CHECK_OFFSET(si_perf);
>   
>   	/* sigpoll */
>   	CHECK_OFFSET(si_band);

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland