From: Willy Tarreau <w@1wt.eu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: about prandom vs __this_cpu_read()
Date: Tue, 13 Oct 2020 04:55:29 +0200 [thread overview]
Message-ID: <20201013025529.GA12006@1wt.eu> (raw)
Linus,
the latest prandom series I sent you changes __this_cpu_read() to
this_cpu_read() since LKP returned the following trace on i386:
[ 9.061912] dump_stack+0x54/0x6e
[ 9.061912] check_preemption_disabled+0xb1/0xc0
[ 9.061912] __this_cpu_preempt_check+0xf/0x11
[ 9.065516] __igt_reserve+0x91/0x580
[ 9.065516] igt_reserve+0x5b/0xc0
[ 9.065516] test_drm_mm_init+0x78/0xa9
I got another report that it breaks on ARC (trivial fix consists in
adding irqflags.h in prandom.h) but that made me wonder, we're using
this to access and update the net_rand_noise variable only, wouldn't
it be better to use the faster raw_cpu_read()/raw_cpu_write() there,
considering we don't care about concurrent accesses since they simply
add even more impredictability to the noise ?
If so, I'll update this branch and will send you another PR.
Thanks,
Willy
reply other threads:[~2020-10-13 2:55 UTC|newest]
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