From: Al Viro Date: Sat, 19 Apr 2014 18:44:49 +0000 (-0400) Subject: acct: encode_comp_t(0) is 0, fortunately... X-Git-Tag: v3.17-rc1~44^2~39 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=ecfdb33d1fbc7e6e095ba24dac2930208494e734;p=platform%2Fkernel%2Flinux-exynos.git acct: encode_comp_t(0) is 0, fortunately... There was an amusing bogosity in ac_rw calculation - it tried to do encode_comp_t(encode_comp_t(0) / 1024). Seeing that comp_t is a 3-bit exponent + 13-bit mantissa... it's a good thing that 0 is represented by all-bits-clear. The history of that one is interesting - it was introduced in 2.1.68pre1, when acct.c had been reworked and moved to separate file. Two months later (2.1.86) somebody has noticed that the sucker won't compile - there was no task_struct::io_usage. At which point the ac_io calculation had changed from encode_comp_t(current->io_usage) to encode_comp_t(0) and the bug in the next line (absolutely real back then, had it ever managed to compile) become a harmless bogosity. Looks like nobody has ever noticed until now. Anyway, let's bury that idiocy now that it got noticed. 17 years is long enough... Signed-off-by: Al Viro --- diff --git a/kernel/acct.c b/kernel/acct.c index a1844f1..807ebc5 100644 --- a/kernel/acct.c +++ b/kernel/acct.c @@ -531,9 +531,6 @@ static void do_acct_process(struct bsd_acct_struct *acct, ac.ac_majflt = encode_comp_t(pacct->ac_majflt); ac.ac_exitcode = pacct->ac_exitcode; spin_unlock_irq(¤t->sighand->siglock); - ac.ac_io = encode_comp_t(0 /* current->io_usage */); /* %% */ - ac.ac_rw = encode_comp_t(ac.ac_io / 1024); - ac.ac_swaps = encode_comp_t(0); /* * Get freeze protection. If the fs is frozen, just skip the write