The patch titled
lib/div64.c: document that div64_u64() is not precise on 32bit platforms
has been added to the -mm tree. Its filename is
lib-div64c-document-that-div64_u64-is-not-precise-on-32bit-platforms.patch
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Subject: lib/div64.c: document that div64_u64() is not precise on 32bit platforms
From: Oleg Nesterov <oleg@xxxxxxxxxx>
We have a bug report which blames div64_u64() on 32bit platforms.
However, the code obviously doesn't even try to pretend it can do the
64bit division precisely. If there is something in the high word of
divisor, div64_u64() just shifts both arguments and throws out the low
bits.
Add a small comment to avoid the confusion.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Ben Woodard <bwoodard@xxxxxxxx>
Cc: Brian Behlendorf <behlendorf1@xxxxxxxx>
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Cc: Mark Grondona <mgrondona@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/div64.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff -puN lib/div64.c~lib-div64c-document-that-div64_u64-is-not-precise-on-32bit-platforms lib/div64.c
--- a/lib/div64.c~lib-div64c-document-that-div64_u64-is-not-precise-on-32bit-platforms
+++ a/lib/div64.c
@@ -77,7 +77,10 @@ s64 div_s64_rem(s64 dividend, s32 diviso
EXPORT_SYMBOL(div_s64_rem);
#endif
-/* 64bit divisor, dividend and result. dynamic precision */
+/*
+ * 64bit divisor, dividend and result. Dynamic precision, unless
+ * divisor fits in u32 result is not exactly correct.
+ */
#ifndef div64_u64
u64 div64_u64(u64 dividend, u64 divisor)
{
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
linux-next.patch
oom-check-pf_kthread-instead-of-mm-to-skip-kthreads.patch
oom-pf_exiting-check-should-take-mm-into-account.patch
oom-introduce-find_lock_task_mm-to-fix-mm-false-positives.patch
oom-dump_tasks-use-find_lock_task_mm-too.patch
oom-improve-commentary-in-dump_tasks.patch
oom-dump_tasks-use-find_lock_task_mm-too-dump_tasks-use-find_lock_task_mm-too-fix.patch
oom-sacrifice-child-with-highest-badness-score-for-parent-protect-dereferencing-of-tasks-comm.patch
oom-sacrifice-child-with-highest-badness-score-for-parent-fix.patch
oom-select-task-from-tasklist-for-mempolicy-ooms-add-has_intersects_mems_allowed-uma-variant.patch
oom-select-task-from-tasklist-for-mempolicy-ooms-introduce-find_lock_task_mm-to-fix-mm-false-positives-fix.patch
oom-dont-try-to-kill-oom_unkillable-child.patch
oom-oom_kill_process-doesnt-select-kthread-child.patch
oom-make-oom_unkillable_task-helper-function.patch
oom-oom_kill_process-needs-to-check-that-p-is-unkillable.patch
oom-proc-pid-oom_score-treat-kernel-thread-honestly.patch
oom-kill-duplicate-oom_disable-check.patch
oom-move-oom_disable-check-from-oom_kill_task-to-out_of_memory.patch
oom-cleanup-has_intersects_mems_allowed.patch
oom-remove-child-mm-check-from-oom_kill_process.patch
oom-give-the-dying-task-a-higher-priority.patch
oom-multi-threaded-process-coredump-dont-make-deadlock.patch
oom-move-badness-declaration-into-oomh.patch
oom-move-badness-declaration-into-oomh-fix.patch
oom-badness-heuristic-rewrite.patch
oom-deprecate-oom_adj-tunable.patch
sys_personality-remove-the-bogus-checks-in-sys_personality-__set_personality-path.patch
x86-ia64-smp-use-workqueues-unconditionally-during-do_boot_cpu.patch
lib-div64c-document-that-div64_u64-is-not-precise-on-32bit-platforms.patch
memcg-use-find_lock_task_mm-in-memory-cgroups-oom.patch
ptrace-optimize-exit_ptrace-for-the-likely-case.patch
pids-alloc_pidmap-remove-the-unnecessary-boundary-checks.patch
aio-do-not-return-erestartsys-and-friends-from-aio.patch
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