Message-ID: <1793713.atdPhlSkOF@opensuse>
Date:   Sun, 05 Jun 2022 17:11:48 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     dsterba@...e.cz, Christoph Hellwig <hch@...radead.org>,
        "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Ira Weiny <ira.weiny@...el.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] btrfs: Replace kmap() with kmap_local_page()

On giovedì 2 giugno 2022 18:28:40 CEST David Sterba wrote:
> On Thu, Jun 02, 2022 at 08:20:08AM -0700, Christoph Hellwig wrote:
> > Turns out that while this looks good, it actually crashes when
> > running xfstests.  I think this is due to the fact that kmap sets
> > the page address, which kmap_local_page does not.
> > 
> > btrfs/150 1s ... [  168.252943] run fstests btrfs/150 at 2022-06-02 
15:17:11
> > [  169.462292] BTRFS info (device vdb): flagging fs with big metadata 
feature
> > [  169.463728] BTRFS info (device vdb): disk space caching is enabled
> > [  169.464953] BTRFS info (device vdb): has skinny extents
> > [  170.596218] BTRFS: device fsid 37c6bae1-d3e5-47f8-87d5-87cd7240a1b4
> > devid 1 transid 5 /dev)
> > [  170.599471] BTRFS: device fsid 37c6bae1-d3e5-47f8-87d5-87cd7240a1b4 
devid 2 transid 5 /dev)
> > [  170.657170] BTRFS info (device vdc): flagging fs with big metadata 
feature
> > [  170.659509] BTRFS info (device vdc): use zlib compression, level 3
> > [  170.661190] BTRFS info (device vdc): disk space caching is enabled
> > [  170.670706] BTRFS info (device vdc): has skinny extents
> > [  170.714181] BTRFS info (device vdc): checking UUID tree
> > [  170.735058] BUG: kernel NULL pointer dereference, address: 
0000000000000008
> > [  170.736478] #PF: supervisor read access in kernel mode
> > [  170.737457] #PF: error_code(0x0000) - not-present page
> > [  170.738529] PGD 0 P4D 0 
> > [  170.739211] Oops: 0000 [#1] PREEMPT SMP PTI
> > [  170.740101] CPU: 0 PID: 43 Comm: kworker/u4:3 Not tainted 5.18.0-
rc7+ #1539
> > [  170.741478] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), 
BIOS 1.14.0-2 04/01/2014
> > [  170.743246] Workqueue: btrfs-delalloc btrfs_work_helper
> > [  170.744282] RIP: 0010:zlib_compress_pages+0x128/0x670
> 
> I've just hit the crash too, so I've removed the patches from misc-next
> until there's fixed version.
> 
Finally I've been able to run xfstests on a QEMU + KVM 32 bits VM. Since I 
have very little experience with filesystems it was a bit hard to setup and 
run.

I can confirm that the problems are only from conversions in patch 3/3. 

Since I've been spending long time to setup xfstests and make it run, I 
haven't yet had time to address the issued in patch 3/3 and making the 
further changes I've been asked for.

Can you please start with taking only patches 1/3 and 2/3 and dropping 3/3?
I'd really appreciate it because, if you can, I'll see that part of my work 
has already been helpful somewhat and have no need to carry those patches 
on to the next series :-) 

The next series will contain everything it has been left out, so that it 
will complete the conversions to local mappings in fs/btrfs. However I will  
need some days more to be done with this task.

I'd like to share the output of xfstests on "compress" group + test 150 
(which is not in that group, although it is the test that both you and 
Christoph ran and which seems to be the only one failing).
 
tweed32:/usr/lib/xfstests # ./check -g compress
FSTYP         -- btrfs
PLATFORM      -- Linux/i686 tweed32 5.18.0-torvalds-debug-x86_32+ #7 SMP 
PREEMPT_DYNAMIC Sat Jun 4 23:47:27 CEST 2022
MKFS_OPTIONS  -- /dev/loop1
MOUNT_OPTIONS -- /dev/loop1 /mnt/scratch

btrfs/024 2s ...  6s
btrfs/026 5s ...  8s
btrfs/037 3s ...  5s
btrfs/038 3s ...  6s
btrfs/041 3s ...  5s
btrfs/062        39s
btrfs/063        21s
btrfs/067        34s
btrfs/068        12s
btrfs/070       [not run] btrfs and this test needs 5 or more disks in 
SCRATCH_DEV_POOL
btrfs/071       [not run] btrfs and this test needs 5 or more disks in 
SCRATCH_DEV_POOL
btrfs/072        37s
btrfs/073        22s
btrfs/074        39s
btrfs/076 2s ...  2s
btrfs/103 3s ...  3s
btrfs/106 3s ...  3s
btrfs/109 2s ...  3s
btrfs/113 3s ...  3s
btrfs/138 47s ...  48s
btrfs/149 3s ...  3s
btrfs/183 3s ...  3s
btrfs/205 3s ...  4s
btrfs/234 4s ...  5s
btrfs/246 3s ...  2s
btrfs/251 2s ...  3s
Ran: btrfs/024 btrfs/026 btrfs/037 btrfs/038 btrfs/041 btrfs/062 btrfs/063 
btrfs/067 btrfs/068 btrfs/070 btrfs/071 btrfs/072 btrfs/073 btrfs/074 
btrfs/076 btrfs/103 btrfs/106 btrfs/109 btrfs/113 btrfs/138 btrfs/149 
btrfs/183 btrfs/205 btrfs/234 btrfs/246 btrfs/251
Not run: btrfs/070 btrfs/071
Passed all 26 tests

tweed32:/usr/lib/xfstests # ./check tests/btrfs/150
FSTYP         -- btrfs
PLATFORM      -- Linux/i686 tweed32 5.18.0-torvalds-debug-x86_32+ #7 SMP 
PREEMPT_DYNAMIC Sat Jun 4 23:47:27 CEST 2022
MKFS_OPTIONS  -- /dev/loop1
MOUNT_OPTIONS -- /dev/loop1 /mnt/scratch

btrfs/150 2s ...  2s
Ran: btrfs/150
Passed all 1 tests

tweed32:/usr/lib/xfstests # cat results/btrfs/150.dmesg
[ 2461.321352] run fstests btrfs/150 at 2022-06-05 16:11:18
[ 2461.718527] BTRFS: device fsid 9337d043-0ca4-4890-b294-7e9505ee13b9 
devid 1 transid 6 /dev/loop1 scanned by systemd-udevd (31060)
[ 2461.721721] BTRFS: device fsid 9337d043-0ca4-4890-b294-7e9505ee13b9 
devid 2 transid 6 /dev/loop2 scanned by mkfs.btrfs (31508)
[ 2461.730540] BTRFS info (device loop1): flagging fs with big metadata 
feature
[ 2461.730543] BTRFS info (device loop1): use zlib compression, level 3
[ 2461.730544] BTRFS info (device loop1): using free space tree
[ 2461.730545] BTRFS info (device loop1): has skinny extents
[ 2461.739677] BTRFS info (device loop1): checking UUID tree
[ 2461.916511] BTRFS info (device loop1): flagging fs with big metadata 
feature
[ 2461.916515] BTRFS info (device loop1): using free space tree
[ 2461.916516] BTRFS info (device loop1): has skinny extents

Please let me know if you require further tests on patches 1/3 and 2/3 and 
on the next series.

Thanks,

Fabio

P.S.: The rest of this message has some details about the kernel and the 
CPU and memory of the VM these tests have been run on. I suppose these 
stats are not so much interesting, so feel free to skip them :-)

tweed32:/usr/lib/xfstests # uname -a
Linux tweed32 5.18.0-torvalds-debug-x86_32+ #7 SMP PREEMPT_DYNAMIC Sat Jun 
4 23:47:27 CEST 2022 i686 athlon i386 GNU/Linux

tweed32:/usr/lib/xfstests # cat /proc/cpuinfo 
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 6
model           : 6
model name      : QEMU Virtual CPU version 2.5+
stepping        : 3
microcode       : 0x1000065
cpu MHz         : 3699.978
physical id     : 0
siblings        : 1
core id         : 0
cpu cores       : 1
apicid          : 0
initial apicid  : 0
fdiv_bug        : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 4
wp              : yes
flags           : fpu de pse tsc msr pae mce cx8 apic sep pge cmov pat mmx 
fxsr sse sse2 cpuid tsc_known_freq pni x2apic hypervisor vmmcall
bugs            : fxsave_leak sysret_ss_attrs spectre_v1 spectre_v2 
spec_store_bypass
bogomips        : 7402.28
clflush size    : 32
cache_alignment : 32
address sizes   : 36 bits physical, 32 bits virtual
power management:

processor       : 1
vendor_id       : AuthenticAMD
cpu family      : 6
model           : 6
model name      : QEMU Virtual CPU version 2.5+

OK, no need to go on with the other CPUs. 
The total amount of virtual CPU is 4. 

tweed32:/usr/lib/xfstests # cat /proc/meminfo 
MemTotal:        4011272 kB
MemFree:         2949956 kB
MemAvailable:    3148368 kB
Buffers:           15700 kB
Cached:           298640 kB
SwapCached:            0 kB
Active:           115992 kB
Inactive:         727008 kB
Active(anon):      21300 kB
Inactive(anon):   538392 kB
Active(file):      94692 kB
Inactive(file):   188616 kB
Unevictable:        3088 kB
Mlocked:               0 kB
HighTotal:       3286900 kB <- Highmem looks enabled properly
HighFree:        2436812 kB
LowTotal:         724372 kB
LowFree:          513144 kB
SwapTotal:       2098152 kB
SwapFree:        2094536 kB
Dirty:               188 kB
Writeback:             0 kB
AnonPages:        531784 kB
Mapped:           218340 kB
Shmem:             31032 kB
KReclaimable:      63896 kB
Slab:             181828 kB
SReclaimable:      63896 kB
SUnreclaim:       117932 kB
KernelStack:        4280 kB
PageTables:        15992 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:     4103788 kB
Committed_AS:    4012104 kB
VmallocTotal:     122880 kB
VmallocUsed:        1468 kB
VmallocChunk:          0 kB
Percpu:             6304 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
Hugetlb:               0 kB
DirectMap4k:      907256 kB
DirectMap2M:           0 kB

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