linux-ext4 - Re: [PATCH] jbd2: wake up journal waiters in FIFO order, not LIFO

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Date:   Thu, 8 Sep 2022 14:41:16 +0530
From:   "Ritesh Harjani (IBM)" <ritesh.list@...il.com>
To:     Alexey Lyahkov <alexey.lyashkov@...il.com>
Cc:     linux-ext4 <linux-ext4@...r.kernel.org>,
        Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger@...ger.ca>,
        Artem Blagodarenko <artem.blagodarenko@...il.com>,
        Andrew Perepechko <anserper@...ru>
Subject: Re: [PATCH] jbd2: wake up journal waiters in FIFO order, not  LIFO

On 22/09/08 11:21AM, Alexey Lyahkov wrote:
> 
> 
> > On 8 Sep 2022, at 09:11, Ritesh Harjani (IBM) <ritesh.list@...il.com> wrote:
> > 
> > On 22/09/08 08:51AM, Alexey Lyahkov wrote:
> >> Hi Ritesh,
> >> 
> >> This was hit on the Lustre OSS node when we have ton’s of short write with sync/(journal commit) in parallel.
> >> Each write was done from own thread (like 1k-2k threads in parallel).
> >> It caused a situation when only few/some threads make a wakeup and enter to the transaction until it will be T_LOCKED.
> >> In our’s observation all handles from head was waked and it’s handles added recently, while old handles still in list and
> > 
> > Thanks Alexey for providing the details.
> > 
> >> It caused a soft lockup messages on console.
> > 
> > Did you mean hung task timeout? I was wondering why will there be soft lockup
> > warning, because these old handles are anyway in a waiting state right.
> > Am I missing something?
> > 
> Oh. I asked a colleges about details. It was internal lustre hung detector not a kernel side

Thanks again for sharing the details. This indeed looks like a task handle can
remain in wait state for long due to wrong wakeup order in case of many threads. 

-ritesh

> 
> [ 2221.036503] Lustre: ll_ost_io04_080: service thread pid 55122 was inactive for 80.284 seconds. The thread might be hung, or it might only be slow and will resume later. Dumping the stack trace for debugging purposes:
> [ 2221.036677] Pid: 55212, comm: ll_ost_io05_074 4.18.0-305.10.2.x6.1.010.19.x86_64 #1 SMP Thu Jun 30 13:42:51 MDT 2022
> [ 2221.056673] Lustre: Skipped 2 previous similar messages
> [ 2221.067821] Call Trace TBD:
> [ 2221.067855] [<0>] wait_transaction_locked+0x89/0xc0 [jbd2]
> [ 2221.099175] [<0>] add_transaction_credits+0xd4/0x290 [jbd2]
> [ 2221.105266] [<0>] start_this_handle+0x10a/0x520 [jbd2]
> [ 2221.110904] [<0>] jbd2__journal_start+0xea/0x1f0 [jbd2]
> [ 2221.116679] [<0>] __ldiskfs_journal_start_sb+0x6e/0x130 [ldiskfs]
> [ 2221.123316] [<0>] osd_trans_start+0x13b/0x4f0 [osd_ldiskfs]
> [ 2221.129417] [<0>] ofd_commitrw_write+0x620/0x1830 [ofd]
> [ 2221.135147] [<0>] ofd_commitrw+0x731/0xd80 [ofd]
> [ 2221.140420] [<0>] obd_commitrw+0x1ac/0x370 [ptlrpc]
> [ 2221.145858] [<0>] tgt_brw_write+0x1913/0x1d50 [ptlrpc]
> [ 2221.151561] [<0>] tgt_request_handle+0xc93/0x1a40 [ptlrpc]
> [ 2221.157622] [<0>] ptlrpc_server_handle_request+0x323/0xbd0 [ptlrpc]
> [ 2221.164454] [<0>] ptlrpc_main+0xc06/0x1560 [ptlrpc]
> [ 2221.169860] [<0>] kthread+0x116/0x130
> [ 2221.174033] [<0>] ret_from_fork+0x1f/0x40
> 
> 
> Other logs have shown this thread can’t take a handle, but other threads able to do it many times.
> Kernel detector don’t hit because thread have wakeup many times but it have seen T_LOCKED and go to sleep again.
> 
> Alex
> 
> 
> 
> > -ritesh
>