The patch titled
Subject: kernel/fork.c: avoid division by zero
has been added to the -mm tree. Its filename is
kernel-forkc-avoid-division-by-zero.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/kernel-forkc-avoid-division-by-zero.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/kernel-forkc-avoid-division-by-zero.patch
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------------------------------------------------------
From: Heinrich Schuchardt <xypron.glpk@xxxxxx>
Subject: 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.
Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/fork.c | 35 ++++++++++++++++++++++++++---------
1 file changed, 26 insertions(+), 9 deletions(-)
diff -puN kernel/fork.c~kernel-forkc-avoid-division-by-zero kernel/fork.c
--- a/kernel/fork.c~kernel-forkc-avoid-division-by-zero
+++ a/kernel/fork.c
@@ -88,6 +88,16 @@
#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)
*/
unsigned long total_forks; /* Handle normal Linux uptimes. */
@@ -258,18 +268,25 @@ void __init __weak arch_task_cache_init(
*/
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);
+
+ if (threads > MAX_THREADS)
+ threads = MAX_THREADS;
+
+ if (threads < MIN_THREADS)
+ threads = MIN_THREADS;
+
+ max_threads = (int) threads;
}
void __init fork_init(void)
_
Patches currently in -mm which might be from xypron.glpk@xxxxxx are
kernel-forkc-new-function-for-max_threads.patch
kernel-forkc-avoid-division-by-zero.patch
kernel-forkc-avoid-division-by-zero-fix.patch
kernel-sysctlc-threads-max-observe-limits.patch
doc-sysctl-kerneltxt-document-threads-max.patch
doc-sysctl-kerneltxt-document-threads-max-fix.patch
linux-next.patch
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