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charset=us-ascii Content-Disposition: inline In-Reply-To: <20240902111446.GG4723@noisy.programming.kicks-ass.net> On 02/09/24 13:14, Peter Zijlstra wrote: > On Thu, Aug 29, 2024 at 10:14:02AM +0200, Juri Lelli wrote: > > Hi, > > > > On 29/08/24 11:11, Huang Shijie wrote: > > > When we enable the schedstats, we will meet an OS hang like this: > > > -------------------------------------------------------- > > > [ 134.104253] kernel BUG at kernel/sched/deadline.c:63! > > > [ 134.132013] ------------[ cut here ]------------ > > > [ 134.133441] x27: 0000000000000001 > > > [ 134.138048] kernel BUG at kernel/sched/deadline.c:63! > > > [ 134.146478] x26: 0000000000000001 x25: 0000000000000000 x24: 0000000000000001 > > > [ 134.153607] x23: 0000000000000001 x22: 0000000000000000 x21: 0000000000000001 > > > [ 134.160734] x20: ffff007dbf1b6d00 x19: ffff007dbf1b7610 x18: 0000000000000014 > > > [ 134.162027] ------------[ cut here ]------------ > > > [ 134.167861] x17: 000000009deab6cd x16: 00000000527c9a1c x15: 00000000000000dc > > > [ 134.172473] kernel BUG at kernel/sched/deadline.c:63! > > > [ 134.179595] x14: 0000000001200011 x13: 0000000040001000 x12: 0000ffffb6df05bc > > > [ 134.191760] x11: ffff007dbf1b6d00 x10: ffff0001062dd2e8 x9 : ffff8000801215ac > > > [ 134.192036] ------------[ cut here ]------------ > > > [ 134.198888] x8 : 0000000000000000 x7 : 0000000000000021 x6 : ffff0001764ed280 > > > [ 134.203498] kernel BUG at kernel/sched/deadline.c:63! > > > [ 134.210622] x5 : 0000000000000000 x4 : 0000000000000001 x3 : ffff807d3dd24000 > > > [ 134.222787] x2 : 000000028b77a140 x1 : 0000003400000000 x0 : ffff007dbf1b6c80 > > > [ 134.229915] Call trace: > > > [ 134.232353] dl_task_of.part.0+0x0/0x10 > > > [ 134.236182] dl_server_start+0x54/0x158 > > > [ 134.240013] enqueue_task_fair+0x138/0x420 > > > [ 134.244100] enqueue_task+0x44/0xb0 > > > [ 134.247584] wake_up_new_task+0x1c0/0x3a0 > > > [ 134.251584] kernel_clone+0xe8/0x3e8 > > > [ 134.252022] ------------[ cut here ]------------ > > > [ 134.255156] __do_sys_clone+0x70/0xa8 > > > [ 134.259764] kernel BUG at kernel/sched/deadline.c:63! > > > [ 134.263412] __arm64_sys_clone+0x28/0x40 > > > [ 134.272360] invoke_syscall+0x50/0x120 > > > [ 134.276101] el0_svc_common+0x44/0xf8 > > > [ 134.279753] do_el0_svc+0x28/0x40 > > > [ 134.283058] el0_svc+0x40/0x150 > > > [ 134.286195] el0t_64_sync_handler+0x100/0x130 > > > [ 134.290546] el0t_64_sync+0x1a4/0x1a8 > > > [ 134.294200] Code: 35ffffa2 17ffffe3 d4210000 17ffffb4 (d4210000) > > > [ 134.300283] ---[ end trace 0000000000000000 ]--- > > > [ 134.304890] Kernel panic - not syncing: Oops - BUG: Fatal exception > > > [ 134.311147] SMP: stopping secondary CPUs > > > [ 135.365096] SMP: failed to stop secondary CPUs 8-9,16,30,43,86,88,121,149 > > > [ 135.371884] Kernel Offset: disabled > > > [ 135.375361] CPU features: 0x00,00100003,80153d29,d75ffea7 > > > [ 135.380749] Memory Limit: none > > > [ 135.383793] ---[ end Kernel panic - not syncing: Oops - BUG: Fatal exception ] > > > -------------------------------------------------------- > > > > > > In dl_server_start(), we set the dl_se->dl_server with 1. When schedstats > > > is enabled, in the following: > > > dl_server_start() --> enqueue_dl_entity() --> update_stats_enqueue_dl() > > > __schedstats_from_dl_se() -->dl_task_of() > > > > > > we will meet the BUG_ON. > > > > > > Since the fair task has already had its own schedstats, there is no need > > > to track anything for the associated dl_server. > > > > > > So add check in: > > > update_stats_wait_start_dl() > > > update_stats_wait_end_dl() > > > update_stats_enqueue_dl() > > > update_stats_dequeue_dl() > > > > > > return early for a dl_server dl_se. > > > > > > Tested this patch with memcached in Altra. > > > > > > Fixes: 5f6bd380c7bd ("sched/rt: Remove default bandwidth control") > > > Signed-off-by: Huang Shijie > > > --- > > > v2 --> v3: > > > Return early in: > > > update_stats_wait_start_dl() > > > update_stats_wait_end_dl() > > > update_stats_enqueue_dl() > > > update_stats_dequeue_dl() > > > > This looks better, thanks. > > > > Peter, what do you think? > > Peter thinks that the Changelog is overly verbose, the Fixes tag is > wrong and he doesn't much like the repeated conditions. But he is very > glad this issue is found and fixed. :) > As such, he's rewritten things like so, does this work for people? Works for me! > --- > Subject: sched/deadline: Fix schedstats vs deadline servers > From: Huang Shijie > Date: Thu, 29 Aug 2024 11:11:11 +0800 > > From: Huang Shijie > > In dl_server_start(), when schedstats is enabled, the following > happens: > > dl_server_start() > dl_se->dl_server = 1; > enqueue_dl_entity() > update_stats_enqueue_dl() > __schedstats_from_dl_se() > dl_task_of() > BUG_ON(dl_server(dl_se)); > > Since only tasks have schedstats and internal entries do not, avoid > trying to update stats in this case. > > Fixes: 63ba8422f876 ("sched/deadline: Introduce deadline servers") > Signed-off-by: Huang Shijie > Signed-off-by: Peter Zijlstra (Intel) > Link: https://lkml.kernel.org/r/20240829031111.12142-1-shijie@os.amperecomputing.com Acked-by: Juri Lelli Thanks, Juri