Commit ac1b398d authored by Heinrich Schuchardt's avatar Heinrich Schuchardt Committed by Linus Torvalds
Browse files

kernel/fork.c: avoid division by zero 



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 32-bit calculation there is no solution which delivers valid results
for all possible combinations of the parameters.  The code is only called
once.  Hence a 64-bit calculation can be used as solution.

[akpm@linux-foundation.org: use clamp_t(), per Oleg]
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 ff691f6e

kernel/fork.c

+20 −9
Original line number Original line Diff line number Diff line
@@ -87,6 +87,16 @@ 
#define CREATE_TRACE_POINTS

#define CREATE_TRACE_POINTS

#include <trace/events/task.h>

#include <trace/events/task.h>





/*

 * Minimum number of threads to boot the kernel

 */

#define MIN_THREADS 20



/*

 * Maximum number of threads

 */

#define MAX_THREADS FUTEX_TID_MASK



/*

/*

 * Protected counters by write_lock_irq(&tasklist_lock)

 * Protected counters by write_lock_irq(&tasklist_lock)

 */

 */
@@ -258,18 +268,19 @@ void __init __weak arch_task_cache_init(void) { } 
 */

 */

static void set_max_threads(void)

static void set_max_threads(void)

{

{

	/*

	u64 threads;

	 * 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

	 * The number of threads shall be limited such that the thread

	 * structures may only consume a small part of the available memory.

	 */

	 */

	if (max_threads < 20)

	if (fls64(totalram_pages) + fls64(PAGE_SIZE) > 64)

		max_threads = 20;

		threads = MAX_THREADS;

	else

		threads = div64_u64((u64) totalram_pages * (u64) PAGE_SIZE,

				    (u64) THREAD_SIZE * 8UL);



	max_threads = clamp_t(u64, threads, MIN_THREADS, MAX_THREADS);

}

}





void __init fork_init(void)

void __init fork_init(void)

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