On 11/19/2015 12:20 PM, Dave Anderson wrote:
>
>
> ----- Original Message -----
>> On 11/19/2015 08:37 AM, David Mair wrote:
>>> On 11/19/2015 07:45 AM, Dave Anderson wrote:
>>>
>>> Hi Dave,
>>>
>>>> ----- Original Message -----
>>> <snip>
>>>>
>>>>> (2) Execute "crash -d8" on physical machine will cause crash utility core
>>>>> dump.
>>>>
>>>> I can reproduce this, so I'll look into it. It's related to the /dev/mem "test"
>>>> to determine whether the kernel was configured with CONFIG_STRICT_DEVMEM, where
>>>> it tries to read from pfn 257 (just above the CONFIG_STRICT_DEVMEM limit), but
>>>> gets into an infinite loop when used in conjunction with -d.
>>>>
>>>> Anyway, just continue to use /proc/kcore and you should be fine.
>>>
>>> This is the cause in readmem():
>>>
>>> switch(READMEM(...))
>>> {
>>> .
>>> .
>>> .
>>> case READ_ERROR:
>>> if (PRINT_ERROR_MESSAGE) ********** THIS ***********
>>> {
>>> causes a nested readmem() call before the goto gives it
>>> to the caller to deal with
>>> }
>>> goto readmem_error
>>> }
>>> .
>>> .
>>> .
>>> switch(error_handle)
>>> {
>>> case (RETURN_ON_ERROR):
>>> }
>>>
>>> The PRINT_ERROR_MESSAGE I assume is an escalation from -d 8 in this case.
>>>
>>
>> The whole switch_to_proc_kcore() probably shouldn't be conditional on
>> the presence of PRINT_ERROR_MESSAGE, only the actual error message
>> should be.
>>
>> Patch shortly.
>>
>> --
>> David.
>
> Yeah, I agree. It was done that way to catch the very first non-QUIET readmem()
> call from kernel_init(), and make the bait-and-switch right there. Without the
> CRASHDEBUG(x) override, it works as-is because the readmem() calls in
> devmem_is_restricted() are purposely set to QUIET.
>
> So we're thinking something like this, right?:
>
> diff --git a/memory.c b/memory.c
> index 824b3ae..2282ba9 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -2207,13 +2207,12 @@ readmem(ulonglong addr, int memtype, void *buffer, long size,
> goto readmem_error;
>
> case READ_ERROR:
> - if (PRINT_ERROR_MESSAGE) {
> - if ((pc->flags & DEVMEM) && (kt->flags & PRE_KERNEL_INIT) &&
> - devmem_is_restricted() && switch_to_proc_kcore())
> - return(readmem(addr, memtype, bufptr, size,
> - type, error_handle));
> + if ((pc->flags & DEVMEM) && (kt->flags & PRE_KERNEL_INIT) &&
> + !(error_handle & QUIET) && devmem_is_restricted() && switch_to_proc_kcore())
> + return(readmem(addr, memtype, bufptr, size,
> + type, error_handle));
> + if (PRINT_ERROR_MESSAGE)
> error(INFO, READ_ERRMSG, memtype_string(memtype, 0), addr, type);
> - }
> goto readmem_error;
>
> case PAGE_EXCLUDED:
>
> Works for me, and is better than hiding a recursive-call check in devmem_is_restricted().
That protects from nesting devmem_is_restricted() as long as
devmem_is_restricted() continues to do QUIET readmem()s but fails to
switch_to_proc_kcore() for QUIET readmem() at other random failing
addresses that could be fixed via /proc/kcore. QUIET isn't a global flag
only for being in devmem_is_restricted().
Here's mine, it's the kind of clumsy hardcore you were trying to avoid,
it's not thread or signal safe. I do feel the same concern you expressed
but I believe it does work for all failing QUIET readmem() cases.
diff --git a/memory.c b/memory.c
index 72218e7..71f1e47 100644
--- a/memory.c
+++ b/memory.c
@@ -319,6 +319,7 @@ static void dump_hstates(void);
#define ASCII_UNLIMITED ((ulong)(-1) >> 1)
static ulong DISPLAY_DEFAULT;
+static int IN_DEVMEM_IS_RESTRICTED;
/*
* Verify that the sizeof the primitive types are reasonable.
@@ -338,6 +339,7 @@ mem_init(void)
error(FATAL, "pointer size: %d is not sizeof(long):
%d\n", sizeof(void *), sizeof(long));
DISPLAY_DEFAULT = (sizeof(long) == 8) ? DISPLAY_64 : DISPLAY_32;
+ IN_DEVMEM_IS_RESTRICTED = FALSE;
}
@@ -2204,13 +2206,13 @@ readmem(ulonglong addr, int memtype, void
*buffer, long size,
goto readmem_error;
case READ_ERROR:
- if (PRINT_ERROR_MESSAGE) {
- if ((pc->flags & DEVMEM) && (kt->flags & PRE_KERNEL_INIT) &&
- devmem_is_restricted() && switch_to_proc_kcore())
- return(readmem(addr, memtype, bufptr, size,
- type, error_handle));
+ if (PRINT_ERROR_MESSAGE)
error(INFO, READ_ERRMSG, memtype_string(memtype, 0), addr, type);
- }
+
+ if ((pc->flags & DEVMEM) && (kt->flags & PRE_KERNEL_INIT) &&
+ devmem_is_restricted() && switch_to_proc_kcore())
+ return(readmem(addr, memtype, bufptr, size,
+ type, error_handle));
goto readmem_error;
case PAGE_EXCLUDED:
@@ -2393,6 +2395,11 @@ devmem_is_restricted(void)
long tmp;
int restricted;
+ if (IN_DEVMEM_IS_RESTRICTED)
+ return FALSE;
+ IN_DEVMEM_IS_RESTRICTED = TRUE;
+
+ restricted = FALSE;
/*
* Check for pre-CONFIG_STRICT_DEVMEM kernels.
@@ -2401,11 +2408,9 @@ devmem_is_restricted(void)
if (machine_type("ARM") || machine_type("ARM64") ||
machine_type("X86") || machine_type("X86_64") ||
machine_type("PPC") || machine_type("PPC64"))
- return FALSE;
+ goto end_devmem_is_restricted;
}
- restricted = FALSE;
-
if (STREQ(pc->live_memsrc, "/dev/mem")) {
if (machine_type("X86") || machine_type("X86_64")) {
if (readmem(255*PAGESIZE(), PHYSADDR, &tmp,
@@ -2429,6 +2434,9 @@ devmem_is_restricted(void)
"source.\n");
}
+end_devmem_is_restricted:
+ IN_DEVMEM_IS_RESTRICTED = FALSE;
+
return restricted;
}
--
Crash-utility mailing list
Crash-utility@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/crash-utility
