Hi,
When you pass an initrd to UML and the size of the initrd is too big for
the current kernel memory, a panic() call is done with the message("Out
of memory").
But this message never hits the stdout as the following stack trace
dumps because there is no current_thread_info() in the UML stack, which
is still active at this time:
(gdb) bt
#0 dump_stack_print_info (log_lvl=0x6053f583 "\001d") at
kernel/printk/printk.c:2979
#1 0x000000006047126b in __dump_stack () at lib/dump_stack.c:14
#2 dump_stack () at lib/dump_stack.c:50
#3 0x000000006046bf87 in panic (fmt=<optimized out>) at kernel/panic.c:110
#4 0x0000000060010bc7 in ___alloc_bootmem (limit=<optimized out>,
goal=<optimized out>, align=<optimized out>, size=<optimized out>) a
t mm/bootmem.c:674
#5 __alloc_bootmem (size=55792228, align=<optimized out>, goal=<optimized
out>) at mm/bootmem.c:696
#6 0x0000000060004eca in read_initrd () at arch/um/kernel/initrd.c:39
#7 0x0000000060004b71 in uml_postsetup () at arch/um/kernel/um_arch.c:228
#8 linux_main (argc=<optimized out>, argv=0x7fffffffdf98) at
arch/um/kernel/um_arch.c:377
#9 0x00000000600059db in main (argc=<optimized out>, argv=0x7fffffffdf98,
envp=<optimized out>) at arch/um/os-Linux/main.c:156
So current_thread_info() will return the stack of the UML program
itself, which is an invalid struct thread_info:
thread info= 0x7fffffffc000
so the access to current->pid, will segfault as "current" is a macro for
current_thread_info()->task->pid and task is NULL.
2978│ void dump_stack_print_info(const char *log_lvl)
2979│ {
2980│ struct thread_info * ti = current_thread_info();
2981│ printf("thread info =%p\n", ti);
2982│
2983│ printk("%sCPU: %d PID: %d Comm: %.20s %s %s %.*s\n",
2984│ log_lvl, raw_smp_processor_id(), current->pid,
current->comm,
2985│ print_tainted(), init_utsname()->release,
2986├> (int)strcspn(init_utsname()->version, " "),
2987│ init_utsname()->version);
any ideas how to fix this?
I tried to add this, but this failed horribly:
diff --git a/arch/um/include/asm/thread_info.h
b/arch/um/include/asm/thread_info.h
--- a/arch/um/include/asm/thread_info.h
+++ b/arch/um/include/asm/thread_info.h
@@ -12,6 +12,11 @@
#include <asm/page.h>
#include <asm/uaccess.h>
+#define DEBUG_CHECK_CURRENT_TI
+#ifdef DEBUG_CHECK_CURRENT_TI
+#include <kern_util.h>
+#endif
+
struct thread_info {
struct task_struct *task; /* main task structure */
struct exec_domain *exec_domain; /* execution domain */
@@ -53,6 +59,12 @@ static inline struct thread_info *current_thread_info(void)
asm volatile ("" : "=r" (p) : "0" (&ti));
ti = (struct thread_info *) (((unsigned long)p) & ~mask);
+#ifdef DEBUG_CHECK_CURRENT_TI
+ if(!is_kernel_addr((void*)ti)) {
+ printk(KERN_CRIT "Access to current_thread_info() from
non-kernel stack!\n");
+// return &init_thread_info;
+ }
+#endif
return ti;
}
diff --git a/arch/um/include/shared/kern_util.h
b/arch/um/include/shared/kern_util.h
index 83a91f9..545503e 100644
--- a/arch/um/include/shared/kern_util.h
+++ b/arch/um/include/shared/kern_util.h
@@ -19,6 +19,7 @@ extern int kmalloc_ok;
#define UML_ROUND_UP(addr) \
((((unsigned long) addr) + PAGE_SIZE - 1) & PAGE_MASK)
+extern int is_kernel_addr(void* addr);
extern unsigned long alloc_stack(int order, int atomic);
extern void free_stack(unsigned long stack, int order);
diff --git a/arch/um/os-Linux/main.c b/arch/um/os-Linux/main.c
index df9191a..a1caebb 100644
--- a/arch/um/os-Linux/main.c
+++ b/arch/um/os-Linux/main.c
@@ -254,7 +255,7 @@ void __wrap_free(void *ptr)
* there is a possibility for memory leaks.
*/
- if ((addr >= uml_physmem) && (addr < high_physmem)) {
+ if (is_kernel_addr(addr)) {
if (kmalloc_ok)
kfree(ptr);
}
@@ -264,3 +265,10 @@ void __wrap_free(void *ptr)
}
else __real_free(ptr);
}
+
+int is_kernel_addr(void* addr)
+{
+ if((addr >= uml_physmem) && (addr < high_physmem))
+ return 1;
+ return 0;
+}
\ No newline at end of file
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