[2.6 patch] fix arm26 THREAD_SIZE

[2.6 patch] fix arm26 THREAD_SIZE

[Adrian Bunk]

arm26 currently has a 256 kB THREAD_SIZE (sic).

Looking at the comment in the code, this seems to be based on a 
misunderstanding.

The comment says:
this needs attention (see kernel/fork.c which gets a nice div by zero if 
this is lower than 8*32768

kernel/fork.c does:
  max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE)

Therefore, a division by 0 is impossible for all reasonable cases with
THREAD_SIZE >= PAGE_SIZE.

Since the minimum PAGE_SIZE Linux uses on the arm26 architecture is 16k, 
PAGE_SIZE should be sufficient for THREAD_SIZE.


Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Ian Molton <spyro@f2s.com>

---

This patch was already sent on:
- Fri, 6 Jan 2006

--- linux-2.6.15-mm1-full/include/asm-arm26/thread_info.h.old	2006-01-06 16:45:40.000000000 +0100
+++ linux-2.6.15-mm1-full/include/asm-arm26/thread_info.h	2006-01-06 16:46:07.000000000 +0100
@@ -80,8 +80,7 @@
 	return (struct thread_info *)(sp & ~0x1fff);
 }
 
-/* FIXME - PAGE_SIZE < 32K */
-#define THREAD_SIZE		(8*32768) // FIXME - this needs attention (see kernel/fork.c which gets a nice div by zero if this is lower than 8*32768
+#define THREAD_SIZE	PAGE_SIZE
 #define task_pt_regs(task) ((struct pt_regs *)(task_stack_page(task) + THREAD_SIZE - 8) - 1)
 
 extern struct thread_info *alloc_thread_info(struct task_struct *task);

[2.6 patch] fix arm26 THREAD_SIZE

[Adrian Bunk]

arm26 currently has a 256 kB THREAD_SIZE (sic).

Looking at the comment in the code, this seems to be based on a 
misunderstanding.

The comment says:
this needs attention (see kernel/fork.c which gets a nice div by zero if 
this is lower than 8*32768

kernel/fork.c does:
  max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE)

Therefore, a division by 0 is impossible for all reasonable cases with
THREAD_SIZE >= PAGE_SIZE.

Since the minimum PAGE_SIZE Linux uses on the arm26 architecture is 16k, 
PAGE_SIZE should be sufficient for THREAD_SIZE.


Signed-off-by: Adrian Bunk <bunk@stusta.de>

--- linux-2.6.15-mm1-full/include/asm-arm26/thread_info.h.old	2006-01-06 16:45:40.000000000 +0100
+++ linux-2.6.15-mm1-full/include/asm-arm26/thread_info.h	2006-01-06 16:46:07.000000000 +0100
@@ -80,8 +80,7 @@
 	return (struct thread_info *)(sp & ~0x1fff);
 }
 
-/* FIXME - PAGE_SIZE < 32K */
-#define THREAD_SIZE		(8*32768) // FIXME - this needs attention (see kernel/fork.c which gets a nice div by zero if this is lower than 8*32768
+#define THREAD_SIZE	PAGE_SIZE
 #define task_pt_regs(task) ((struct pt_regs *)(task_stack_page(task) + THREAD_SIZE - 8) - 1)
 
 extern struct thread_info *alloc_thread_info(struct task_struct *task);

Re: [2.6 patch] fix arm26 THREAD_SIZE

[Ian Molton]

Adrian Bunk wrote:

Looks good to me. cant recall why that got that way, but the div by zero 
definately went away at the time. certainly its wrong as-is, the 
implication is that an 8 MB machine would get a max_threads of about 4 :)

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Ian Molton <spyro@f2s.com>

--- linux-2.6.15-mm1-full/include/asm-arm26/thread_info.h.old	2006-01-06 
16:45:40.000000000 +0100
+++ linux-2.6.15-mm1-full/include/asm-arm26/thread_info.h	2006-01-06 
16:46:07.000000000 +0100
@@ -80,8 +80,7 @@
  	return (struct thread_info *)(sp & ~0x1fff);
  }

-/* FIXME - PAGE_SIZE < 32K */
-#define THREAD_SIZE		(8*32768) // FIXME - this needs attention (see 
kernel/fork.c which gets a nice div by zero if this is lower than 8*32768
+#define THREAD_SIZE	PAGE_SIZE
  #define task_pt_regs(task) ((struct pt_regs *)(task_stack_page(task) + 
THREAD_SIZE - 8) - 1)

  extern struct thread_info *alloc_thread_info(struct task_struct *task);