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kernel/fork.c: avoid division by zero

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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: Heinrich 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Heinrich Schuchardt 2015-04-16 12:47:47 -07:00 committed by Linus Torvalds
parent ff691f6e03
commit ac1b398de1
1 changed files with 20 additions and 9 deletions
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29
kernel/fork.c
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@ -87,6 +87,16 @@
#define CREATE_TRACE_POINTS
#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)
*/
@ -258,18 +268,19 @@ void __init __weak arch_task_cache_init(void) { }
*/
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);
u64 threads;
/*
* 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)
max_threads = 20;
if (fls64(totalram_pages) + fls64(PAGE_SIZE) > 64)
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)