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Commit ff691f6e authored by Heinrich Schuchardt's avatar Heinrich Schuchardt Committed by Linus Torvalds
Browse files

kernel/fork.c: new function for max_threads 



PAGE_SIZE is not guaranteed to be equal to or less than 8 times the
THREAD_SIZE.

E.g.  architecture hexagon may have page size 1M and thread size 4096.
This would lead to a division by zero in the calculation of max_threads.

With this patch the buggy code is moved to a separate function
set_max_threads.  The error is not fixed.

After fixing the problem in a separate patch the new function can be
reused to adjust max_threads after adding or removing memory.

Argument mempages of function fork_init() is removed as totalram_pages is
an exported symbol.

The creation of separate patches for refactoring to a new function and for
fixing the logic was suggested by Ingo Molnar.

Signed-off-by: default avatarHeinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3ea7f5e2

init/main.c

+2 −2
Original line number Diff line number Diff line
@@ -91,7 +91,7 @@ 
static int kernel_init(void *);



extern void init_IRQ(void);

extern void fork_init(unsigned long);

extern void fork_init(void);

extern void radix_tree_init(void);

#ifndef CONFIG_DEBUG_RODATA

static inline void mark_rodata_ro(void) { }
@@ -645,7 +645,7 @@ asmlinkage __visible void __init start_kernel(void) 
#endif

	thread_info_cache_init();

	cred_init();

	fork_init(totalram_pages);

	fork_init();

	proc_caches_init();

	buffer_init();

	key_init();

kernel/fork.c

+21 −13
Original line number Diff line number Diff line
@@ -253,7 +253,26 @@ EXPORT_SYMBOL_GPL(__put_task_struct); 


void __init __weak arch_task_cache_init(void) { }



void __init fork_init(unsigned long mempages)

/*

 * set_max_threads

 */

static void set_max_threads(void)

{

	/*

	 * The default maximum number of threads is set to a safe

	 * value: the thread structures can take up at most one

	 * eighth of the memory.

	 */

	max_threads = totalram_pages / (8 * THREAD_SIZE / PAGE_SIZE);



	/*

	 * we need to allow at least 20 threads to boot a system

	 */

	if (max_threads < 20)

		max_threads = 20;

}



void __init fork_init(void)

{

#ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR

#ifndef ARCH_MIN_TASKALIGN
@@ -268,18 +287,7 @@ void __init fork_init(unsigned long mempages) 
	/* do the arch specific task caches init */

	arch_task_cache_init();



	/*

	 * The default maximum number of threads is set to a safe

	 * value: the thread structures can take up at most one

	 * eighth of the memory.

	 */

	max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);



	/*

	 * we need to allow at least 20 threads to boot a system

	 */

	if (max_threads < 20)

		max_threads = 20;

	set_max_threads();



	init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;

	init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;