[PATCH] uml: fix TT mode by reverting "use fork instead of clone"
With Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Revert the following patch, because of miscompilation problems in different
environments leading to UML not working *at all* in TT mode; it was merged
lately in 2.6 development cycle, a little after being written, and has
caused problems to lots of people; I know it's a bit too long, but it
shouldn't have been merged in first place, so I still apply for inclusion
in the -stable tree. Anyone using this feature currently is either using
some older kernel (some reports even used 2.6.12-rc4-mm2) or using this
patch, as included in my -bs patchset.
For now there's not yet a fix for this patch, so for now the best thing is
to drop it (which was widely reported to give a working kernel, and as such
was even merged in -stable tree).
"Convert the boot-time host ptrace testing from clone to fork. They were
essentially doing fork anyway. This cleans up the code a bit, and makes
valgrind a bit happier about grinding it."
URL:
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=98fdffccea6cc3fe9dba32c0fcc310bcb5d71529
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index 8b01a55..67acd92 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -131,7 +131,7 @@
return(arg.pid);
}
-static int ptrace_child(void)
+static int ptrace_child(void *arg)
{
int ret;
int pid = os_getpid(), ppid = getppid();
@@ -160,16 +160,20 @@
_exit(ret);
}
-static int start_ptraced_child(void)
+static int start_ptraced_child(void **stack_out)
{
+ void *stack;
+ unsigned long sp;
int pid, n, status;
- pid = fork();
- if(pid == 0)
- ptrace_child();
-
+ stack = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if(stack == MAP_FAILED)
+ panic("check_ptrace : mmap failed, errno = %d", errno);
+ sp = (unsigned long) stack + PAGE_SIZE - sizeof(void *);
+ pid = clone(ptrace_child, (void *) sp, SIGCHLD, NULL);
if(pid < 0)
- panic("check_ptrace : fork failed, errno = %d", errno);
+ panic("check_ptrace : clone failed, errno = %d", errno);
CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
if(n < 0)
panic("check_ptrace : wait failed, errno = %d", errno);
@@ -177,6 +181,7 @@
panic("check_ptrace : expected SIGSTOP, got status = %d",
status);
+ *stack_out = stack;
return(pid);
}
@@ -184,12 +189,12 @@
* just avoid using sysemu, not panic, but only if SYSEMU features are broken.
* So only for SYSEMU features we test mustpanic, while normal host features
* must work anyway!*/
-static int stop_ptraced_child(int pid, int exitcode, int mustexit)
+static int stop_ptraced_child(int pid, void *stack, int exitcode, int mustpanic)
{
int status, n, ret = 0;
if(ptrace(PTRACE_CONT, pid, 0, 0) < 0)
- panic("stop_ptraced_child : ptrace failed, errno = %d", errno);
+ panic("check_ptrace : ptrace failed, errno = %d", errno);
CATCH_EINTR(n = waitpid(pid, &status, 0));
if(!WIFEXITED(status) || (WEXITSTATUS(status) != exitcode)) {
int exit_with = WEXITSTATUS(status);
@@ -200,13 +205,15 @@
printk("check_ptrace : child exited with exitcode %d, while "
"expecting %d; status 0x%x", exit_with,
exitcode, status);
- if (mustexit)
+ if (mustpanic)
panic("\n");
else
printk("\n");
ret = -1;
}
+ if(munmap(stack, PAGE_SIZE) < 0)
+ panic("check_ptrace : munmap failed, errno = %d", errno);
return ret;
}
@@ -242,11 +249,12 @@
static void __init check_sysemu(void)
{
+ void *stack;
int pid, syscall, n, status, count=0;
printk("Checking syscall emulation patch for ptrace...");
sysemu_supported = 0;
- pid = start_ptraced_child();
+ pid = start_ptraced_child(&stack);
if(ptrace(PTRACE_SYSEMU, pid, 0, 0) < 0)
goto fail;
@@ -264,7 +272,7 @@
panic("check_sysemu : failed to modify system "
"call return, errno = %d", errno);
- if (stop_ptraced_child(pid, 0, 0) < 0)
+ if (stop_ptraced_child(pid, stack, 0, 0) < 0)
goto fail_stopped;
sysemu_supported = 1;
@@ -272,7 +280,7 @@
set_using_sysemu(!force_sysemu_disabled);
printk("Checking advanced syscall emulation patch for ptrace...");
- pid = start_ptraced_child();
+ pid = start_ptraced_child(&stack);
while(1){
count++;
if(ptrace(PTRACE_SYSEMU_SINGLESTEP, pid, 0, 0) < 0)
@@ -297,7 +305,7 @@
break;
}
}
- if (stop_ptraced_child(pid, 0, 0) < 0)
+ if (stop_ptraced_child(pid, stack, 0, 0) < 0)
goto fail_stopped;
sysemu_supported = 2;
@@ -308,17 +316,18 @@
return;
fail:
- stop_ptraced_child(pid, 1, 0);
+ stop_ptraced_child(pid, stack, 1, 0);
fail_stopped:
printk("missing\n");
}
void __init check_ptrace(void)
{
+ void *stack;
int pid, syscall, n, status;
printk("Checking that ptrace can change system call numbers...");
- pid = start_ptraced_child();
+ pid = start_ptraced_child(&stack);
if (ptrace(PTRACE_OLDSETOPTIONS, pid, 0, (void *)PTRACE_O_TRACESYSGOOD) < 0)
panic("check_ptrace: PTRACE_SETOPTIONS failed, errno = %d", errno);
@@ -345,7 +354,7 @@
break;
}
}
- stop_ptraced_child(pid, 0, 1);
+ stop_ptraced_child(pid, stack, 0, 1);
printk("OK\n");
check_sysemu();
}
@@ -380,10 +389,11 @@
static inline void check_skas3_ptrace_support(void)
{
struct ptrace_faultinfo fi;
+ void *stack;
int pid, n;
printf("Checking for the skas3 patch in the host...");
- pid = start_ptraced_child();
+ pid = start_ptraced_child(&stack);
n = ptrace(PTRACE_FAULTINFO, pid, 0, &fi);
if (n < 0) {
@@ -402,7 +412,7 @@
}
init_registers(pid);
- stop_ptraced_child(pid, 1, 1);
+ stop_ptraced_child(pid, stack, 1, 1);
}
int can_do_skas(void)
