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Date: Thu, 17 Mar 2022 11:01:29 -0700 From: "Paul E. McKenney" <paulmck@...nel.org> To: Oliver Sang <oliver.sang@...el.com> Cc: lkp@...ts.01.org, lkp@...el.com, LKML <linux-kernel@...r.kernel.org> Subject: Re: [fixup! EXP srcu] 7bf8d644f8: WARNING:at_kernel/rcu/srcutree.c:#process_srcu On Thu, Mar 17, 2022 at 03:16:08PM +0800, Oliver Sang wrote: > hi, Paul, > > On Wed, Mar 16, 2022 at 09:53:42AM -0700, Paul E. McKenney wrote: > > On Mon, Mar 14, 2022 at 01:38:14PM -0700, Paul E. McKenney wrote: > > > On Sat, Mar 12, 2022 at 11:59:19PM +0800, kernel test robot wrote: > > > > > > > > > > > > Greeting, > > > > > > > > FYI, we noticed the following commit (built with gcc-9): > > > > > > > > commit: 7bf8d644f869260f63eaaedebabdd2054f59ecc4 ("fixup! EXP srcu: Check for too many zero-delay srcu_reschedule() calls") > > > > https://github.com/ammarfaizi2/linux-block paulmck/linux-rcu/dev.2022.03.01a > > > > > > > > in testcase: boot > > > > > > > > on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G > > > > > > > > caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace): > > > > > > > > > > > > > > > > If you fix the issue, kindly add following tag > > > > Reported-by: kernel test robot <oliver.sang@...el.com> > > > > > > > > > > > > [ 27.088275][ T42] WARNING: CPU: 1 PID: 42 at kernel/rcu/srcutree.c:1555 process_srcu (kernel/rcu/srcutree.c:1555 (discriminator 3)) > > > > [ 27.089252][ T42] Modules linked in: libata(+) serio_raw i2c_piix4 parport_pc(+) parport ip_tables > > > > [ 27.090253][ T42] CPU: 1 PID: 42 Comm: kworker/1:1 Not tainted 5.17.0-rc1-00191-g7bf8d644f869 #1 > > > > [ 27.091212][ T42] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 > > > > [ 27.092176][ T42] Workqueue: rcu_gp process_srcu > > > > [ 27.092718][ T42] RIP: 0010:process_srcu (kernel/rcu/srcutree.c:1555 (discriminator 3)) > > > > [ 27.093653][ T42] Code: 6b f8 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 0f 85 91 02 00 00 48 8b 43 f8 31 f6 48 83 f8 32 0f 86 02 fe ff ff <0f> 0b e9 fb fd ff ff 4c 8d b3 58 ff ff ff 48 b8 00 00 00 00 00 fc > > > > > > I had a feeling that the simple fix wasn't going to cut it, so thank you > > > for finding a scenario that proves that to be the case. Fix in progress, > > > to be folded into the original with attribution. > > > > OK, the attribution isn't quite there yet, but the squished-together > > commit is here: > > > > ea0098f19115 ("srcu: Prevent expedited GPs and blocking readers from consuming CPU") > > > > Does this version behave better for you? > > we tested this commit, found the issue gone. > please be noted the issue on 7bf8d644f8 is random and ~25% rate. > so I queued to run 100 times for this new commit, which is finally clean > according to tests. > > ========================================================================================= > compiler/kconfig/rootfs/sleep/tbox_group/testcase: > gcc-9/x86_64-rhel-8.3-func/debian-10.4-x86_64-20200603.cgz/1/vm-snb/boot > > commit: > feebd043ec6b ("Revert "srcu: Avoid expedited GPs and blocking readers from consuming CPU"") > 7bf8d644f869 ("fixup! EXP srcu: Check for too many zero-delay srcu_reschedule() calls") > ea0098f19115 ("srcu: Prevent expedited GPs and blocking readers from consuming CPU") > > feebd043ec6b9eab 7bf8d644f869260f63eaaedebab ea0098f191152c7fe3db5181a2e > ---------------- --------------------------- --------------------------- > fail:runs %reproduction fail:runs %reproduction fail:runs > | | | | | > :16 25% 4:16 0% :100 dmesg.RIP:process_srcu > :16 25% 4:16 0% :100 dmesg.WARNING:at_kernel/rcu/srcutree.c:#process_srcu Thank you for testing this! Tested-by? Thanx, Paul
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