RFR: 8294003: Don't handle si_addr == 0 && si_code == SI_KERNEL SIGSEGVs

[Aleksey Shipilev]

On Wed, 21 Sep 2022 13:55:48 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> I think x86_32 can/should do the same, because faulting on bona fide incorrect address currently produces a misleading error, see below.

So I think we can just drop the entirety of `#ifndef` block:


diff --git a/src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp b/src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp
index 31afbe696a2..9cd0b9a8b58 100644
--- a/src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp
+++ b/src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp
@@ -220,17 +220,9 @@ bool PosixSignals::pd_hotspot_signal_handler(int sig, siginfo_t* info,
     pc = (address) os::Posix::ucontext_get_pc(uc);
 
     if (sig == SIGSEGV && info->si_addr == 0 && info->si_code == SI_KERNEL) {
-#ifndef AMD64
-    // Halt if SI_KERNEL before more crashes get misdiagnosed as Java bugs
-    // This can happen in any running code (currently more frequently in
-    // interpreter code but has been seen in compiled code)
-      fatal("An irrecoverable SI_KERNEL SIGSEGV has occurred due "
-            "to unstable signal handling in this distribution.");
-#else
       // An irrecoverable SI_KERNEL SIGSEGV has occurred.
       // It's likely caused by dereferencing an address larger than TASK_SIZE.
       return false;
-#endif
     }
 
     // Handle ALL stack overflow variations here


On the test above, x86_32 failure before:


#
# A fatal error has been detected by the Java Runtime Environment:
#
#  Internal Error (os_linux_x86.cpp:227), pid=1007, tid=1008
#  fatal error: An irrecoverable SI_KERNEL SIGSEGV has occurred due to unstable signal handling in this distribution.
#
# JRE version: OpenJDK Runtime Environment (20.0) (build 20-testing-builds.shipilev.net-openjdk-jdk-b210-20220919)
# Java VM: OpenJDK Server VM (20-testing-builds.shipilev.net-openjdk-jdk-b210-20220919, mixed mode, sharing, tiered, serial gc, linux-x86)
# Problematic frame:
# V  [libjvm.so+0xa095be]  PosixSignals::pd_hotspot_signal_handler(int, siginfo_t*, ucontext_t*, JavaThread*)+0x40e
...
---------------  T H R E A D  ---------------

Current thread (0xb6a162d0):  JavaThread "main" [_thread_in_vm, id=1008, stack(0xb6bda000,0xb6c2b000)]

Stack: [0xb6bda000,0xb6c2b000],  sp=0xb6c29810,  free space=318k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V  [libjvm.so+0xa095be]  PosixSignals::pd_hotspot_signal_handler(int, siginfo_t*, ucontext_t*, JavaThread*)+0x40e  (os_linux_x86.cpp:227)
V  [libjvm.so+0xb477fa]  JVM_handle_linux_signal+0x15a  (signals_posix.cpp:655)
V  [libjvm.so+0xb47a23]  javaSignalHandler(int, siginfo_t*, void*)+0x23  (signals_posix.cpp:683)
C  [linux-gate.so.1+0x570]  __kernel_rt_sigreturn+0x0
J 860  jdk.internal.misc.Unsafe.getInt(Ljava/lang/Object;J)I java.base at 20-testing (0 bytes) @ 0xaf3706e3 [0xaf370620+0x000000c3]
j  jdk.internal.misc.Unsafe.getInt(J)I+3 java.base at 20-testing
j  sun.misc.Unsafe.getInt(J)I+4 jdk.unsupported at 20-testing
j  Crash.main([Ljava/lang/String;)V+26


x86_32 failure after:


# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0xb78f5f53, pid=710, tid=711
#
# JRE version: OpenJDK Runtime Environment (20.0) (build 20-internal-adhoc.buildbot.openjdk-jdk)
# Java VM: OpenJDK Server VM (20-internal-adhoc.buildbot.openjdk-jdk, mixed mode, sharing, tiered, serial gc, linux-x86)
# Problematic frame:
# V  [libjvm.so+0xc35f53]  Unsafe_GetInt+0xa3

Current thread (0xb6a162c0):  JavaThread "main" [_thread_in_vm, id=711, stack(0xb6b6b000,0xb6bbc000)]

Stack: [0xb6b6b000,0xb6bbc000],  sp=0xb6bbacf0,  free space=319k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V  [libjvm.so+0xc35f53]  Unsafe_GetInt+0xa3  (unsafe.cpp:223)
J 884  jdk.internal.misc.Unsafe.getInt(Ljava/lang/Object;J)I java.base at 20-internal (0 bytes) @ 0xaf372063 [0xaf371fa0+0x000000c3]
j  jdk.internal.misc.Unsafe.getInt(J)I+3 java.base at 20-internal
j  sun.misc.Unsafe.getInt(J)I+4 jdk.unsupported at 20-internal
j  Crash.main([Ljava/lang/String;)V+26


Current hs_err does not have siginfo printout, while the hs_err with the patch does the proper:


siginfo: si_signo: 11 (SIGSEGV), si_code: 128 (SI_KERNEL), si_addr: 0x00000000

-------------

PR: https://git.openjdk.org/jdk/pull/10340