From ac1b398de1ef94aeee8ba87b0120763526572a6e Mon Sep 17 00:00:00 2001 From: Heinrich Schuchardt Date: Thu, 16 Apr 2015 12:47:47 -0700 Subject: [PATCH] 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: Heinrich Schuchardt Cc: Oleg Nesterov Cc: Ingo Molnar Cc: Guenter Roeck Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/fork.c | 29 ++++++++++++++++++++--------- 1 file changed, 20 insertions(+), 9 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 01038e6f51a8..c7f2e1a4187a 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -87,6 +87,16 @@ #define CREATE_TRACE_POINTS #include +/* + * 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) -- GitLab