linux-ext4 - Re: [v4.14-rc3 bug] scheduling while atomic in generic/451 test on extN

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Message-ID: <20171013132200.dvc33h26ezwqpqwm@rh_laptop>
Date:   Fri, 13 Oct 2017 15:22:00 +0200
From:   Lukas Czerner <lczerner@...hat.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Eryu Guan <eguan@...hat.com>, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org
Subject: Re: [v4.14-rc3 bug] scheduling while atomic in generic/451 test on
 extN

On Fri, Oct 13, 2017 at 12:28:42PM +0200, Lukas Czerner wrote:
> On Thu, Oct 12, 2017 at 05:07:40PM +0200, Jan Kara wrote:
> > Hi Eryu!
> > 
> > On Thu 05-10-17 14:07:00, Eryu Guan wrote:
> > > I hit "scheduling while atomic" bug by running fstests generic/451 on
> > > extN filesystems in v4.14-rc3 testing, but it didn't reproduce for me on
> > > every host I tried, but I've seen it multiple times on multiple hosts. A
> > > test vm of mine with 4 vcpus and 8G memory reproduced the bug reliably,
> > > while a bare metal host with 8 cpus and 8G mem couldn't.
> > > 
> > > This is due to commit 332391a9935d ("fs: Fix page cache inconsistency
> > > when mixing buffered and AIO DIO"), which defers AIO DIO io completion
> > > to a workqueue if the inode has mapped pages and does page cache
> > > invalidation in process context. I think that the problem is that the
> > > pages can be mapped after the dio->inode->i_mapping->nrpages check, so
> > > we're doing page cache invalidation, which could sleep, in interrupt
> > > context, thus "scheduling while atomic" bug happens.
> > > 
> > > Defering all AIO DIO completion to workqueue unconditionally (as what
> > > the iomap based path does) fixed the problem for me. But there're
> > > performance concerns to do so in the original discussions.
> > > 
> > > https://www.spinics.net/lists/linux-fsdevel/msg112669.html
> > 
> > Thanks for report and the detailed analysis. I think your analysis is
> > correct and the nrpages check in dio_bio_end_aio() is racy. My solution to
> > this would be to pass to dio_complete() as an argument whether invalidation
> > is required or not (and set it to true for deferred completion and to false
> > when we decide not to defer completion since nrpages is 0 at that moment).
> > Lukas?

Btw, instead of changing the arguments, can't we just use

if (current->flags & PF_WQ_WORKER)

to make sure we're called from the workqueue ?

-Lukas

> 
> Oops, right I've missed that the nrpages check in dio_bio_end_aio() is
> indeed racy. I'll prepare a patch. Thanks!
> 
> -Lukas
> 
> > 
> > 								Honza
> > 
> > > [17087.868644] BUG: scheduling while atomic: swapper/0/0/0x00000100 
> > > [17087.875363] Modules linked in: dm_thin_pool dm_persistent_data dm_bio_prison dm_snapshot dm_bufio loop dm_flakey dm_mod ses enclosure ext4 mbcache jbd2 intel_rapl sb_edac x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm irqbypass crct10dif_pclmul crc32_pclmul mpt3sas ghash_clmulni_intel raid_class sg scsi_transport_sas pcbc ipmi_ssif shpchp aesni_intel crypto_simd iTCO_wdt glue_helper ipmi_si cryptd iTCO_vendor_support cdc_ether ipmi_devintf ipmi_msghandler usbnet mii pcspkr acpi_pad wmi dcdbas joydev acpi_power_meter lpc_ich mei_me mei nfsd auth_rpcgss nfs_acl lockd grace sunrpc ip_tables xfs libcrc32c mgag200 drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops sd_mod igb ttm ahci ptp libahci drm libata pps_core crc32c_intel dca megaraid_sas i2c_algo_bit i2c_core [last unloaded: scsi_debug] 
> > > [17087.955757] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W       4.14.0-rc3 #1 
> > > [17087.964110] Hardware name: Dell Inc. PowerEdge R620/01W23F, BIOS 2.5.4 01/22/2016 
> > > [17087.972460] Call Trace: 
> > > [17087.975189]  <IRQ> 
> > > [17087.977441]  dump_stack+0x63/0x89 
> > > [17087.981143]  __schedule_bug+0x62/0x70 
> > > [17087.985232]  __schedule+0x7bb/0x890 
> > > [17087.989125]  schedule+0x36/0x80 
> > > [17087.992629]  io_schedule+0x16/0x40 
> > > [17087.996429]  __lock_page+0x10a/0x150 
> > > [17088.000420]  ? page_cache_tree_insert+0xb0/0xb0 
> > > [17088.005470]  invalidate_inode_pages2_range+0x240/0x500 
> > > [17088.011208]  ? kmem_cache_free+0x1ad/0x1c0 
> > > [17088.015778]  ? mempool_free_slab+0x17/0x20 
> > > [17088.020347]  ? mempool_free+0x2b/0x80 
> > > [17088.024438]  dio_complete+0x14f/0x1d0 
> > > [17088.028526]  dio_bio_end_aio+0xcb/0x120 
> > > [17088.032800]  bio_endio+0xa1/0x120 
> > > [17088.036501]  blk_update_request+0xb7/0x310 
> > > [17088.041076]  scsi_end_request+0x34/0x200 
> > > [17088.045454]  scsi_io_completion+0x133/0x5f0 
> > > [17088.050123]  scsi_finish_command+0xd9/0x120 
> > > [17088.054782]  scsi_softirq_done+0x145/0x170 
> > > [17088.059355]  blk_done_softirq+0xa1/0xd0 
> > > [17088.063627]  __do_softirq+0xc9/0x269 
> > > [17088.067619]  irq_exit+0xd9/0xf0 
> > > [17088.071123]  do_IRQ+0x51/0xd0 
> > > [17088.074434]  common_interrupt+0x9d/0x9d 
> > > [17088.078713]  </IRQ> 
> > -- 
> > Jan Kara <jack@...e.com>
> > SUSE Labs, CR