On Tue, Aug 11, 2020 at 09:57:20AM +0200, David Sterba wrote: > On Mon, Aug 10, 2020 at 03:14:30PM -0400, Sasha Levin wrote: > > From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> > > > > [ Upstream commit 9f47eb5461aaeb6cb8696f9d11503ae90e4d5cb0 ] > > > > Very large I/Os can cause the following RCU CPU stall warning: > > > > RIP: 0010:rb_prev+0x8/0x50 > > Code: 49 89 c0 49 89 d1 48 89 c2 48 89 f8 e9 e5 fd ff ff 4c 89 48 10 c3 4c = > > 89 06 c3 4c 89 40 10 c3 0f 1f 00 48 8b 0f 48 39 cf 74 38 <48> 8b 47 10 48 85 c0 74 22 48 8b 50 08 48 85 d2 74 0c 48 89 d0 48 > > RSP: 0018:ffffc9002212bab0 EFLAGS: 00000287 ORIG_RAX: ffffffffffffff13 > > RAX: ffff888821f93630 RBX: ffff888821f93630 RCX: ffff888821f937e0 > > RDX: 0000000000000000 RSI: 0000000000102000 RDI: ffff888821f93630 > > RBP: 0000000000103000 R08: 000000000006c000 R09: 0000000000000238 > > R10: 0000000000102fff R11: ffffc9002212bac8 R12: 0000000000000001 > > R13: ffffffffffffffff R14: 0000000000102000 R15: ffff888821f937e0 > > __lookup_extent_mapping+0xa0/0x110 > > try_release_extent_mapping+0xdc/0x220 > > btrfs_releasepage+0x45/0x70 > > shrink_page_list+0xa39/0xb30 > > shrink_inactive_list+0x18f/0x3b0 > > shrink_lruvec+0x38e/0x6b0 > > shrink_node+0x14d/0x690 > > do_try_to_free_pages+0xc6/0x3e0 > > try_to_free_mem_cgroup_pages+0xe6/0x1e0 > > reclaim_high.constprop.73+0x87/0xc0 > > mem_cgroup_handle_over_high+0x66/0x150 > > exit_to_usermode_loop+0x82/0xd0 > > do_syscall_64+0xd4/0x100 > > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > > On a PREEMPT=n kernel, the try_release_extent_mapping() function's > > "while" loop might run for a very long time on a large I/O. This commit > > therefore adds a cond_resched() to this loop, providing RCU any needed > > quiescent states. > > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > Paul, > > this patch was well hidden in some huge RCU pile > (https://lore.kernel.org/lkml/20200623002147.25750-11-paulmck@xxxxxxxxxx/) > > I wonder why you haven't CCed linux-btrfs, I spotted the patch queued > for stable by incidentally. The timestamp is from June, that's quite > some time ago. We can deal with one more patch and I tend to reply with > acks quickly for easy patches like this to not block other peoples work > but I'm a bit disappointed by sidestepping maintained subsystems. It's > not just this patch, it happens from time time only to increase the > disapointement. My bad, and please accept my apologies. I clearly left out the step of adding proper Cc: lines. :-/ Thanx, Paul
