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 <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>hifive-unleashed-5.1
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ff691f6e03
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ac1b398de1
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@ -87,6 +87,16 @@
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#define CREATE_TRACE_POINTS
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#define CREATE_TRACE_POINTS
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#include <trace/events/task.h>
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#include <trace/events/task.h>
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/*
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* Minimum number of threads to boot the kernel
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*/
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#define MIN_THREADS 20
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/*
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* Maximum number of threads
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*/
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#define MAX_THREADS FUTEX_TID_MASK
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/*
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/*
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* Protected counters by write_lock_irq(&tasklist_lock)
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* Protected counters by write_lock_irq(&tasklist_lock)
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*/
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*/
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@ -258,18 +268,19 @@ void __init __weak arch_task_cache_init(void) { }
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*/
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*/
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static void set_max_threads(void)
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static void set_max_threads(void)
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{
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{
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/*
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u64 threads;
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* The default maximum number of threads is set to a safe
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* value: the thread structures can take up at most one
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* eighth of the memory.
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*/
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max_threads = totalram_pages / (8 * THREAD_SIZE / PAGE_SIZE);
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/*
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/*
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* we need to allow at least 20 threads to boot a system
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* The number of threads shall be limited such that the thread
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* structures may only consume a small part of the available memory.
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*/
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*/
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if (max_threads < 20)
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if (fls64(totalram_pages) + fls64(PAGE_SIZE) > 64)
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max_threads = 20;
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threads = MAX_THREADS;
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else
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threads = div64_u64((u64) totalram_pages * (u64) PAGE_SIZE,
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(u64) THREAD_SIZE * 8UL);
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max_threads = clamp_t(u64, threads, MIN_THREADS, MAX_THREADS);
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}
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}
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void __init fork_init(void)
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void __init fork_init(void)
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