On Mon, 4 Nov 2019 at 17:11, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > > On Mon, Nov 04, 2019 at 12:31:56PM +0100, Marco Elver wrote: > > +RCU folks, since this is probably a data race in RCU. > > > > On Mon, 4 Nov 2019 at 12:29, syzbot > > <syzbot+08f3e9d26e5541e1ecf2@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > Hello, > > > > > > syzbot found the following crash on: > > > > > > HEAD commit: 05f22368 x86, kcsan: Enable KCSAN for x86 > > > git tree: https://github.com/google/ktsan.git kcsan > > > console output: https://syzkaller.appspot.com/x/log.txt?x=17ade7ef600000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=87d111955f40591f > > > dashboard link: https://syzkaller.appspot.com/bug?extid=08f3e9d26e5541e1ecf2 > > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > > > > Unfortunately, I don't have any reproducer for this crash yet. > > > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > > Reported-by: syzbot+08f3e9d26e5541e1ecf2@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > ================================================================== > > > BUG: KCSAN: data-race in process_srcu / synchronize_srcu > > > > > > write to 0xffffffff8604e8a0 of 8 bytes by task 17 on cpu 1: > > > srcu_gp_end kernel/rcu/srcutree.c:533 [inline] > > > srcu_advance_state kernel/rcu/srcutree.c:1146 [inline] > > > process_srcu+0x207/0x780 kernel/rcu/srcutree.c:1237 > > > process_one_work+0x3d4/0x890 kernel/workqueue.c:2269 > > > worker_thread+0xa0/0x800 kernel/workqueue.c:2415 > > > kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253 > > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352 > > > > > > read to 0xffffffff8604e8a0 of 8 bytes by task 12515 on cpu 0: > > > srcu_might_be_idle kernel/rcu/srcutree.c:784 [inline] > > > synchronize_srcu+0x107/0x214 kernel/rcu/srcutree.c:996 > > > fsnotify_connector_destroy_workfn+0x63/0xb0 fs/notify/mark.c:164 > > > process_one_work+0x3d4/0x890 kernel/workqueue.c:2269 > > > worker_thread+0xa0/0x800 kernel/workqueue.c:2415 > > > kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253 > > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352 > > > > > > Reported by Kernel Concurrency Sanitizer on: > > > CPU: 0 PID: 12515 Comm: kworker/u4:8 Not tainted 5.4.0-rc3+ #0 > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > > > Google 01/01/2011 > > > Workqueue: events_unbound fsnotify_connector_destroy_workfn > > > ================================================================== > > > Kernel panic - not syncing: panic_on_warn set ... > > > CPU: 0 PID: 12515 Comm: kworker/u4:8 Not tainted 5.4.0-rc3+ #0 > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > > > Google 01/01/2011 > > > Workqueue: events_unbound fsnotify_connector_destroy_workfn > > > Call Trace: > > > __dump_stack lib/dump_stack.c:77 [inline] > > > dump_stack+0xf5/0x159 lib/dump_stack.c:113 > > > panic+0x210/0x640 kernel/panic.c:221 > > > kcsan_report.cold+0xc/0x10 kernel/kcsan/report.c:302 > > > __kcsan_setup_watchpoint+0x32e/0x4a0 kernel/kcsan/core.c:411 > > > __tsan_read8 kernel/kcsan/kcsan.c:36 [inline] > > > __tsan_read8+0x2c/0x30 kernel/kcsan/kcsan.c:36 > > > srcu_might_be_idle kernel/rcu/srcutree.c:784 [inline] > > > synchronize_srcu+0x107/0x214 kernel/rcu/srcutree.c:996 > > > fsnotify_connector_destroy_workfn+0x63/0xb0 fs/notify/mark.c:164 > > > process_one_work+0x3d4/0x890 kernel/workqueue.c:2269 > > > worker_thread+0xa0/0x800 kernel/workqueue.c:2415 > > > kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253 > > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352 > > > Kernel Offset: disabled > > > Rebooting in 86400 seconds.. > > > > > > > > > --- > > > This bug is generated by a bot. It may contain errors. > > > See https://goo.gl/tpsmEJ for more information about syzbot. > > > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx. > > > > > > syzbot will keep track of this bug report. See: > > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > Good catch! Does the patch below help? Looks good to me, thanks for the quick fix. Acked-by: Marco Elver <elver@xxxxxxxxxx> Thanks, -- Marco > Thanx, Paul > > ------------------------------------------------------------------------ > > commit d2ab457602a59353b8853352735dfd094d223480 > Author: Paul E. McKenney <paulmck@xxxxxxxxxx> > Date: Mon Nov 4 08:08:30 2019 -0800 > > srcu: Apply *_ONCE() to ->srcu_last_gp_end > > The ->srcu_last_gp_end field is accessed from any CPU at any time > by synchronize_srcu(), so non-initialization references need to use > READ_ONCE() and WRITE_ONCE(). This commit therefore makes that change. > > Reported-by: syzbot+08f3e9d26e5541e1ecf2@xxxxxxxxxxxxxxxxxxxxxxxxx > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > index d0a9d5b..657e6a7 100644 > --- a/kernel/rcu/srcutree.c > +++ b/kernel/rcu/srcutree.c > @@ -530,7 +530,7 @@ static void srcu_gp_end(struct srcu_struct *ssp) > idx = rcu_seq_state(ssp->srcu_gp_seq); > WARN_ON_ONCE(idx != SRCU_STATE_SCAN2); > cbdelay = srcu_get_delay(ssp); > - ssp->srcu_last_gp_end = ktime_get_mono_fast_ns(); > + WRITE_ONCE(ssp->srcu_last_gp_end, ktime_get_mono_fast_ns()); > rcu_seq_end(&ssp->srcu_gp_seq); > gpseq = rcu_seq_current(&ssp->srcu_gp_seq); > if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, gpseq)) > @@ -762,6 +762,7 @@ static bool srcu_might_be_idle(struct srcu_struct *ssp) > unsigned long flags; > struct srcu_data *sdp; > unsigned long t; > + unsigned long tlast; > > /* If the local srcu_data structure has callbacks, not idle. */ > local_irq_save(flags); > @@ -780,9 +781,9 @@ static bool srcu_might_be_idle(struct srcu_struct *ssp) > > /* First, see if enough time has passed since the last GP. */ > t = ktime_get_mono_fast_ns(); > + tlast = READ_ONCE(ssp->srcu_last_gp_end); > if (exp_holdoff == 0 || > - time_in_range_open(t, ssp->srcu_last_gp_end, > - ssp->srcu_last_gp_end + exp_holdoff)) > + time_in_range_open(t, tlast, tlast + exp_holdoff)) > return false; /* Too soon after last GP. */ > > /* Next, check for probable idleness. */
