Re: btrfs hang on brd

2011-06-06 Thread Adrian Hunter 

On 03/06/11 12:41, Adrian Hunter wrote:

No improvement on 3.0-rc1+ (commit
5c6cce92bc8aee751aafe82c5d9caf7553226a3d).


And on 59c5f46fbe01a00eedf54a23789634438bb80603 Linux 3.0-rc2
btrfs quickly fails to mount due to no space e.g.


Script
--

#!/bin/sh

sudo modprobe brd rd_size=262144

sudo umount /mnt/test/ 2 /dev/null

echo 'mkfs.btrfs /dev/ram0'

sudo mkfs.btrfs /dev/ram0

sudo mkdir -p /mnt/test

echo 'mount -t btrfs /dev/ram0 /mnt/test'

sudo mount -t btrfs /dev/ram0 /mnt/test

sudo mkdir -p /mnt/test/test

sudo chown $USER /mnt/test/test
sudo chgrp $USER /mnt/test/test

sudo umount /mnt/test

full=0
i=0
while true; do
sudo mount -t btrfs /dev/ram0 /mnt/test

if df | grep ram0 | grep 100%  /dev/null; then
full=`expr $full \+ 1`
if test $full -gt 6;then
rm -rf /mnt/test/test/*
full=0
fi
else
full=0
fi

fsstress -c -r -d /mnt/test/test -p 3 -n 1000 -l 10

sudo umount /mnt/test

i=`expr $i \+ 1`
echo $i
done



Script Output
-

mkfs.btrfs /dev/ram0

WARNING! - Btrfs Btrfs v0.19 IS EXPERIMENTAL
WARNING! - see http://btrfs.wiki.kernel.org before using

fs created label (null) on /dev/ram0
nodesize 4096 leafsize 4096 sectorsize 4096 size 256.00MB
Btrfs Btrfs v0.19
mount -t btrfs /dev/ram0 /mnt/test
1
2
3
4
mount: No space left on device
^C



Kernel messages
---

[   95.084429] brd: module loaded
[   95.368708] Btrfs loaded
[   95.369455] device fsid 9644bae59f78285c-8db3a698a8a82293 devid 1 
transid 7 /dev/ram0

[   95.370582] SELinux: initialized (dev ram0, type btrfs), uses xattr
[   95.487905] device fsid 9644bae59f78285c-8db3a698a8a82293 devid 1 
transid 10 /dev/ram0

[   95.49] SELinux: initialized (dev ram0, type btrfs), uses xattr
[  107.336869] device fsid 9644bae59f78285c-8db3a698a8a82293 devid 1 
transid 2664 /dev/ram0

[  107.338873] SELinux: initialized (dev ram0, type btrfs), uses xattr
[  115.861909] device fsid 9644bae59f78285c-8db3a698a8a82293 devid 1 
transid 6816 /dev/ram0

[  115.864089] SELinux: initialized (dev ram0, type btrfs), uses xattr
[  122.586606] device fsid 9644bae59f78285c-8db3a698a8a82293 devid 1 
transid 10872 /dev/ram0

[  122.587779] SELinux: initialized (dev ram0, type btrfs), uses xattr
[  128.824401] BTRFS: inode 19622 still on the orphan list
[  128.844945] [ cut here ]
[  128.844969] WARNING: at fs/btrfs/extent-tree.c:6878 
btrfs_free_block_groups+0x1e6/0x228 [btrfs]()

[  128.844973] Hardware name: XPS 8300
[  128.844974] Modules linked in: btrfs zlib_deflate libcrc32c brd tun 
fuse cpufreq_ondemand acpi_cpufreq freq_table mperf ip6t_REJECT 
nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables ipv6 uinput 
snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_intel snd_hda_codec 
snd_hwdep snd_seq snd_seq_device snd_pcm broadcom snd_timer snd tg3 
pcspkr joydev iTCO_wdt iTCO_vendor_support soundcore snd_page_alloc 
i2c_i801 serio_raw dcdbas microcode usb_storage i915 drm_kms_helper drm 
i2c_algo_bit i2c_core video [last unloaded: scsi_wait_scan]
[  128.845024] Pid: 2503, comm: umount Not tainted 
3.0.0-rc2-2011-06-06-02+ #13

[  128.845026] Call Trace:
[  128.845035]  [8104db2e] warn_slowpath_common+0x85/0x9d
[  128.845050]  [a02a6b70] ? 
btrfs_free_block_groups+0x204/0x228 [btrfs]

[  128.845056]  [8104db60] warn_slowpath_null+0x1a/0x1c
[  128.845069]  [a02a6b52] btrfs_free_block_groups+0x1e6/0x228 
[btrfs]

[  128.845087]  [a02afa0b] close_ctree+0x22c/0x346 [btrfs]
[  128.845092]  [8103d068] ? should_resched+0xe/0x2e
[  128.845097]  [8147abfe] ? _cond_resched+0xe/0x22
[  128.845100]  [8147b7d5] ? down_write+0x29/0x49
[  128.845110]  [a0295a1e] btrfs_put_super+0x1d/0x2c [btrfs]
[  128.845116]  [8111ecb4] generic_shutdown_super+0x74/0xe9
[  128.845120]  [8111eda9] kill_anon_super+0x16/0x50
[  128.845125]  [8111efd6] deactivate_locked_super+0x26/0x4b
[  128.845129]  [8111f7c5] deactivate_super+0x3a/0x3f
[  128.845133]  [81134a09] mntput_no_expire+0xd0/0xd5
[  128.845136]  [81135688] sys_umount+0x2dc/0x30a
[  128.845141]  [81125c64] ? path_put+0x22/0x27
[  128.845145]  [814828c2] system_call_fastpath+0x16/0x1b
[  128.845149] ---[ end trace e535ebf83dd43354 ]---
[  128.845152] space_info has 8814592 free, is full
[  128.845156] space_info total=41943040, used=24576000, pinned=0, 
reserved=98304, may_use=0, readonly=8454144
[  128.897312] device fsid 9644bae59f78285c-8db3a698a8a82293 devid 1 
transid 14722 /dev/ram0

[  128.910740] BTRFS: inode 19622 still on the orphan list
[  128.910747] btrfs: could not do orphan cleanup -28
[  128.948912] btrfs: open_ctree failed
--
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Re: btrfs hang on brd

2011-06-03 Thread Adrian Hunter 

On 01/06/11 13:07, Adrian Hunter wrote:

On 01/06/11 11:54, David Sterba wrote:

On Tue, May 31, 2011 at 10:03:12AM +0300, Adrian Hunter wrote:

Hi

I seem to be able to get btrfs reproducibly to
produce warnings and finally hang when running
a stress test on a ramdisk.

Testing was done using the integration-test
branch of btrfs-unstable.  Note that I also tested
v2.6.39 and integration-test took much longer to
hang i.e. it is an improvement

The test script and stack dumps are below.

Is this a valid test?

Is it worth me investigating these?


I've tried to reproduce myself, but the fsstress utility (taken from
latest LTP suite) crashes sometimes and I cannot take it as a proper
reproduction. Can you point me to the exact version you used?


The LTP version does not compile properly:

make[4]: Entering directory
`/home/ahunter/Desktop/Projects/ltp/ltp-full-20110228/testcases/kernel/fs/fsstress'

gcc -g -O2 -g -O2 -fno-strict-aliasing -pipe -Wall  -DNO_XFS
-I/home/ahunter/Desktop/Projects/ltp/ltp-full-20110228/testcases/kernel/fs/fsstress
-D_LARGEFILE64_SOURCE -D_GNU_SOURCE -Wno-error -I../../../../include
-I../../../../include   -L../../../../lib  fsstress.c   -o fsstress
fsstress.c: In function 'dread_f':
fsstress.c:1829:2: warning: implicit declaration of function 'memalign'
fsstress.c:1829:6: warning: assignment makes pointer from integer
without a cast
fsstress.c: In function 'dwrite_f':
fsstress.c:1912:6: warning: assignment makes pointer from integer
without a cast
fsstress.c:1844:17: warning: 'diob.d_miniosz' may be used uninitialized
in this function
fsstress.c:1844:17: warning: 'diob.d_maxiosz' may be used uninitialized
in this function
fsstress.c:1844:17: warning: 'diob.d_mem' may be used uninitialized in
this function
fsstress.c: In function 'dread_f':
fsstress.c:1750:17: warning: 'diob.d_miniosz' may be used uninitialized
in this function
fsstress.c:1750:17: warning: 'diob.d_maxiosz' may be used uninitialized
in this function
fsstress.c:1750:17: warning: 'diob.d_mem' may be used uninitialized in
this function


I hacked a couple of changes but I need to check them before
mailing to the ltp-list:


From: Adrian Hunter adrian.hun...@intel.com
Date: Wed, 1 Jun 2011 13:01:48 +0300
Subject: [PATCH] fsstress: quick fix for compile errors

Signed-off-by: Adrian Hunter adrian.hun...@intel.com
---
  testcases/kernel/fs/fsstress/fsstress.c |2 ++
  testcases/kernel/fs/fsstress/global.h   |1 +
  2 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/testcases/kernel/fs/fsstress/fsstress.c
b/testcases/kernel/fs/fsstress/fsstress.c
index e3b48ea..83c23ed 100644
--- a/testcases/kernel/fs/fsstress/fsstress.c
+++ b/testcases/kernel/fs/fsstress/fsstress.c
@@ -1757,6 +1757,7 @@ dread_f(int opno, long r)
  struct stat64stb;
  intv;

+memset(diob, 0, sizeof(struct dioattr));
  init_pathname(f);
  if (!get_fname(FT_REGFILE, r, f, NULL, NULL, v)) {
  if (v)
@@ -1851,6 +1852,7 @@ dwrite_f(int opno, long r)
  struct stat64stb;
  intv;

+memset(diob, 0, sizeof(struct dioattr));
  init_pathname(f);
  if (!get_fname(FT_REGFILE, r, f, NULL, NULL, v)) {
  if (v)
diff --git a/testcases/kernel/fs/fsstress/global.h
b/testcases/kernel/fs/fsstress/global.h
index f788395..5ab5d56 100644
--- a/testcases/kernel/fs/fsstress/global.h
+++ b/testcases/kernel/fs/fsstress/global.h
@@ -58,6 +58,7 @@
  #include stdlib.h
  #include stdio.h
  #include unistd.h
+#include malloc.h

  #ifndef O_DIRECT
  #define O_DIRECT 04
--
1.7.4.4



(But no warning or hang observed, on top of 3.0-rc1 + cmason/for-linus)


I will try it tonight.


No improvement on 3.0-rc1+ (commit 
5c6cce92bc8aee751aafe82c5d9caf7553226a3d).


Logs follow:


Warnings


[ 2857.023360] WARNING: at fs/btrfs/extent-tree.c:5648 
btrfs_alloc_free_block+0x14e/0x357 [btrfs]()

[ 2857.023364] Hardware name: XPS 8300
[ 2857.023367] Modules linked in: tun btrfs zlib_deflate libcrc32c brd 
fuse cpufreq_ondemand acpi_cpufreq freq_table mperf ip6t_REJECT 
nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables ipv6 uinput 
snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_intel snd_hda_codec 
snd_hwdep snd_seq snd_seq_device broadcom snd_pcm snd_timer snd tg3 
iTCO_wdt serio_raw dcdbas iTCO_vendor_support microcode soundcore pcspkr 
snd_page_alloc i2c_i801 joydev usb_storage i915 drm_kms_helper drm 
i2c_algo_bit i2c_core video [last unloaded: scsi_wait_scan]
[ 2857.023431] Pid: 8809, comm: btrfs-endio-wri Not tainted 
3.0.0-rc1-work-2011-06-01-01+ #11

[ 2857.023435] Call Trace:
[ 2857.023461]  [8104db2e] warn_slowpath_common+0x85/0x9d
[ 2857.023471]  [8104db60] warn_slowpath_null+0x1a/0x1c
[ 2857.023494]  [a029cc98] btrfs_alloc_free_block+0x14e/0x357 
[btrfs]
[ 2857.023526]  [a02c75bb] ? 
map_private_extent_buffer+0xb1/0xd5 [btrfs]

[ 2857.023547]  [a028f99f] __btrfs_cow_block+0x102/0x31e [btrfs]
[ 2857.023565]  [a028e500

Re: btrfs hang on brd

2011-06-01 Thread Adrian Hunter 

On 01/06/11 11:54, David Sterba wrote:

On Tue, May 31, 2011 at 10:03:12AM +0300, Adrian Hunter wrote:

Hi

I seem to be able to get btrfs reproducibly to
produce warnings and finally hang when running
a stress test on a ramdisk.

Testing was done using the integration-test
branch of btrfs-unstable.  Note that I also tested
v2.6.39 and integration-test took much longer to
hang i.e. it is an improvement

The test script and stack dumps are below.

Is this a valid test?

Is it worth me investigating these?


I've tried to reproduce myself, but the fsstress utility (taken from
latest LTP suite) crashes sometimes and I cannot take it as a proper
reproduction. Can you point me to the exact version you used?


The LTP version does not compile properly:

make[4]: Entering directory 
`/home/ahunter/Desktop/Projects/ltp/ltp-full-20110228/testcases/kernel/fs/fsstress'
gcc -g -O2 -g -O2 -fno-strict-aliasing -pipe -Wall  -DNO_XFS 
-I/home/ahunter/Desktop/Projects/ltp/ltp-full-20110228/testcases/kernel/fs/fsstress 
-D_LARGEFILE64_SOURCE -D_GNU_SOURCE -Wno-error -I../../../../include 
-I../../../../include   -L../../../../lib  fsstress.c   -o fsstress

fsstress.c: In function 'dread_f':
fsstress.c:1829:2: warning: implicit declaration of function 'memalign'
fsstress.c:1829:6: warning: assignment makes pointer from integer 
without a cast

fsstress.c: In function 'dwrite_f':
fsstress.c:1912:6: warning: assignment makes pointer from integer 
without a cast
fsstress.c:1844:17: warning: 'diob.d_miniosz' may be used uninitialized 
in this function
fsstress.c:1844:17: warning: 'diob.d_maxiosz' may be used uninitialized 
in this function
fsstress.c:1844:17: warning: 'diob.d_mem' may be used uninitialized in 
this function

fsstress.c: In function 'dread_f':
fsstress.c:1750:17: warning: 'diob.d_miniosz' may be used uninitialized 
in this function
fsstress.c:1750:17: warning: 'diob.d_maxiosz' may be used uninitialized 
in this function
fsstress.c:1750:17: warning: 'diob.d_mem' may be used uninitialized in 
this function



I hacked a couple of changes but I need to check them before
mailing to the ltp-list:


From: Adrian Hunter adrian.hun...@intel.com
Date: Wed, 1 Jun 2011 13:01:48 +0300
Subject: [PATCH] fsstress: quick fix for compile errors

Signed-off-by: Adrian Hunter adrian.hun...@intel.com
---
 testcases/kernel/fs/fsstress/fsstress.c |2 ++
 testcases/kernel/fs/fsstress/global.h   |1 +
 2 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/testcases/kernel/fs/fsstress/fsstress.c 
b/testcases/kernel/fs/fsstress/fsstress.c

index e3b48ea..83c23ed 100644
--- a/testcases/kernel/fs/fsstress/fsstress.c
+++ b/testcases/kernel/fs/fsstress/fsstress.c
@@ -1757,6 +1757,7 @@ dread_f(int opno, long r)
struct stat64   stb;
int v;

+   memset(diob, 0, sizeof(struct dioattr));
init_pathname(f);
if (!get_fname(FT_REGFILE, r, f, NULL, NULL, v)) {
if (v)
@@ -1851,6 +1852,7 @@ dwrite_f(int opno, long r)
struct stat64   stb;
int v;

+   memset(diob, 0, sizeof(struct dioattr));
init_pathname(f);
if (!get_fname(FT_REGFILE, r, f, NULL, NULL, v)) {
if (v)
diff --git a/testcases/kernel/fs/fsstress/global.h 
b/testcases/kernel/fs/fsstress/global.h

index f788395..5ab5d56 100644
--- a/testcases/kernel/fs/fsstress/global.h
+++ b/testcases/kernel/fs/fsstress/global.h
@@ -58,6 +58,7 @@
 #include stdlib.h
 #include stdio.h
 #include unistd.h
+#include malloc.h

 #ifndef O_DIRECT
 #define O_DIRECT 04
--
1.7.4.4



(But no warning or hang observed, on top of 3.0-rc1 + cmason/for-linus)


I will try it tonight.

--
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btrfs hang on brd

2011-05-31 Thread Adrian Hunter 

Hi

I seem to be able to get btrfs reproducibly to
produce warnings and finally hang when running
a stress test on a ramdisk.

Testing was done using the integration-test
branch of btrfs-unstable.  Note that I also tested
v2.6.39 and integration-test took much longer to
hang i.e. it is an improvement

The test script and stack dumps are below.

Is this a valid test?

Is it worth me investigating these?

Regards
Adrian



Test


#!/bin/sh

sudo modprobe brd rd_size=262144

sudo umount /mnt/test/ 2 /dev/null

echo 'mkfs.btrfs /dev/ram0'

sudo mkfs.btrfs /dev/ram0

sudo mkdir -p /mnt/test

echo 'mount -t btrfs /dev/ram0 /mnt/test'

sudo mount -t btrfs /dev/ram0 /mnt/test

sudo mkdir -p /mnt/test/test

sudo chown $USER /mnt/test/test
sudo chgrp $USER /mnt/test/test

sudo umount /mnt/test

full=0
i=0
while true; do
sudo mount -t btrfs /dev/ram0 /mnt/test

if df | grep ram0 | grep 100%  /dev/null; then
full=`expr $full \+ 1`
if test $full -gt 6;then
rm -rf /mnt/test/test/*
full=0
fi
else
full=0
fi

fsstress -c -r -d /mnt/test/test -p 3 -n 1000 -l 10

sudo umount /mnt/test

i=`expr $i \+ 1`
echo $i
done



Stack dumps for warnings



[ 7481.520750] WARNING: at fs/btrfs/extent-tree.c:5648 
btrfs_alloc_free_block+0x14e/0x357 [btrfs]()

[ 7481.520753] Hardware name: XPS 8300
[ 7481.520754] Modules linked in: tcp_lp tun btrfs zlib_deflate 
libcrc32c brd fuse cpufreq_ondemand acpi_cpufreq freq_table mperf 
ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables 
ipv6 uinput snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_intel 
snd_hda_codec broadcom tg3 snd_hwdep snd_seq snd_seq_device snd_pcm 
joydev pcspkr iTCO_wdt iTCO_vendor_support dcdbas serio_raw i2c_i801 
snd_timer snd microcode soundcore snd_page_alloc usb_storage i915 
drm_kms_helper drm i2c_algo_bit i2c_core video [last unloaded: 
scsi_wait_scan]
[ 7481.520805] Pid: 3980, comm: btrfs-endio-wri Not tainted 
2.6.39-integration-test-20110526-01+ #2

[ 7481.520808] Call Trace:
[ 7481.520818]  [8104df7a] warn_slowpath_common+0x85/0x9d
[ 7481.520824]  [8104dfac] warn_slowpath_null+0x1a/0x1c
[ 7481.520838]  [a02dfca8] btrfs_alloc_free_block+0x14e/0x357 
[btrfs]
[ 7481.520865]  [a030a073] ? 
map_private_extent_buffer+0xb1/0xd5 [btrfs]

[ 7481.520875]  [a02d2987] __btrfs_cow_block+0x102/0x31e [btrfs]
[ 7481.520883]  [a02d1300] ? btrfs_set_item_key+0x3/0x20 [btrfs]
[ 7481.520892]  [a02d2ca7] btrfs_cow_block+0x104/0x14d [btrfs]
[ 7481.520910]  [a02d5a87] btrfs_search_slot+0x162/0x502 [btrfs]
[ 7481.520925]  [a02e3e66] btrfs_lookup_file_extent+0x3c/0x3e 
[btrfs]

[ 7481.520936]  [a02d2124] ? btrfs_alloc_path+0x1a/0x2b [btrfs]
[ 7481.520955]  [a02f9319] btrfs_drop_extents+0x10e/0x731 [btrfs]
[ 7481.520960]  [8103cc9e] ? need_resched+0x23/0x2d
[ 7481.520966]  [81474da6] ? _cond_resched+0xe/0x22
[ 7481.520972]  [8110d58c] ? 
slab_pre_alloc_hook.clone.32+0x2d/0x31

[ 7481.520977]  [8110e0c7] ? kmem_cache_alloc+0x29/0xf7
[ 7481.521002]  [a02f09fa] 
insert_reserved_file_extent.clone.34+0x70/0x1fc [btrfs]

[ 7481.521027]  [a03071c9] ? lock_extent_bits+0x5e/0xa8 [btrfs]
[ 7481.521044]  [a02f362c] 
btrfs_endio_direct_write+0x171/0x29a [btrfs]

[ 7481.521060]  [a02e6afc] ? end_workqueue_fn+0xf6/0x10e [btrfs]
[ 7481.521065]  [81141934] bio_endio+0x2d/0x2f
[ 7481.521087]  [a02e6b07] end_workqueue_fn+0x101/0x10e [btrfs]
[ 7481.521101]  [a0310951] worker_loop+0x193/0x4ca [btrfs]
[ 7481.521116]  [a03107be] ? btrfs_queue_worker+0x214/0x214 
[btrfs]

[ 7481.521119]  [81068dce] kthread+0x82/0x8a
[ 7481.521124]  [8147db64] kernel_thread_helper+0x4/0x10
[ 7481.521136]  [81068d4c] ? kthread_worker_fn+0x14b/0x14b
[ 7481.521141]  [8147db60] ? gs_change+0x13/0x13
[ 7481.521144] ---[ end trace abb147a5624a0a24 ]---
[ 7481.521161] [ cut here ]
[ 7481.521176] WARNING: at fs/btrfs/extent-tree.c:5648 
btrfs_alloc_free_block+0x14e/0x357 [btrfs]()

[ 7481.521178] Hardware name: XPS 8300
[ 7481.521180] Modules linked in: tcp_lp tun btrfs zlib_deflate 
libcrc32c brd fuse cpufreq_ondemand acpi_cpufreq freq_table mperf 
ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables 
ipv6 uinput snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_intel 
snd_hda_codec broadcom tg3 snd_hwdep snd_seq snd_seq_device snd_pcm 
joydev pcspkr iTCO_wdt iTCO_vendor_support dcdbas serio_raw i2c_i801 
snd_timer snd microcode soundcore snd_page_alloc usb_storage i915 
drm_kms_helper drm i2c_algo_bit i2c_core video [last unloaded: 
scsi_wait_scan]
[ 7481.521237] Pid: 3980, comm: btrfs-endio-wri Tainted: GW 
2.6.39-integration-test-20110526-01+ #2

[

Re: [PATCH] Btrfs: don't commit the transaction if we dont have enough pinned bytes V2

2011-05-26 Thread Adrian Hunter 

On 25/05/11 22:30, Josef Bacik wrote:

I noticed when running an enospc test that we would get stuck committing the
transaction in check_data_space even though we truly didn't have enough space.
So check to see if bytes_pinned is bigger than num_bytes, if it's not don't
commit the transaction.  Thanks,

Signed-off-by: Josef Bacikjo...@redhat.com
---
V1-V2: Make it so it actually compiles ;)
  fs/btrfs/extent-tree.c |7 +++
  1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index c8c3184..b4f67e8 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3199,6 +3199,13 @@ alloc:
}
goto again;
}
+
+   /*
+* If we have less pinned bytes than we want to allocate then
+* don't bother committing the transaction, it won't help us.
+*/
+   if (data_sinfo-bytes_pinned  bytes)
+   committed = 1;
spin_unlock(data_sinfo-lock);

/* commit the current transaction and try again */


I tried that patch on 2.6.39 with the following:

sudo modprobe brd rd_size=262144
sudo mkfs.btrfs /dev/ram0
sudo mkdir -p /mnt/test
sudo mount -t btrfs /dev/ram0 /mnt/test
sudo mkdir -p /mnt/test/test
sudo chown $USER /mnt/test/test
sudo chgrp $USER /mnt/test/test
sudo umount /mnt/test
i=0
while true; do
sudo mount -t btrfs /dev/ram0 /mnt/test
fsstress -c -r -d /mnt/test/test -p 3 -n 1000 -l 10
sudo umount /mnt/test
i=`expr $i \+ 1`
echo $i
done


After 3 iterations it got really slow and then after some minutes it
still seems to lock up:

[ 2059.881182] SysRq : Show Blocked State
[ 2059.881188]   taskPC stack   pid father
[ 2059.881226] btrfs-transacti D 000100046afc 0  2212  2 
0x0080
[ 2059.881233]  880181483d60 0046 0003 
8801
[ 2059.881239]  00013a80 00013a80 00013a80 
880184dac530
[ 2059.881244]  00013a80 880181483fd8 00013a80 
00013a80

[ 2059.881249] Call Trace:
[ 2059.881273]  [a02e8780] wait_for_commit.clone.14+0x90/0xd5 
[btrfs]

[ 2059.881280]  [810692ab] ? wake_up_bit+0x2a/0x2a
[ 2059.881297]  [a02e95b4] 
btrfs_commit_transaction+0x102/0x665 [btrfs]
[ 2059.881312]  [a02e8eae] ? 
join_transaction.clone.21+0x180/0x18b [btrfs]

[ 2059.881316]  [810692ab] ? wake_up_bit+0x2a/0x2a
[ 2059.881331]  [a02e402e] transaction_kthread+0x17a/0x22f [btrfs]
[ 2059.881345]  [a02e3eb4] ? btrfs_congested_fn+0x82/0x82 [btrfs]
[ 2059.881349]  [81068dce] kthread+0x82/0x8a
[ 2059.881355]  [8147db64] kernel_thread_helper+0x4/0x10
[ 2059.881359]  [81068d4c] ? kthread_worker_fn+0x14b/0x14b
[ 2059.881364]  [8147db60] ? gs_change+0x13/0x13
[ 2059.881366] flush-btrfs-5   D 0001000f78a6 0  2219  2 
0x0080
[ 2059.881371]  8801828efb10 0046 0754 
8801
[ 2059.881376]  00013a80 00013a80 00013a80 
8801a53fc530
[ 2059.881382]  00013a80 8801828effd8 00013a80 
00013a80

[ 2059.881386] Call Trace:
[ 2059.881391]  [814750a4] schedule_timeout+0x36/0xe3
[ 2059.881396]  [8107b6c2] ? arch_local_irq_save+0x18/0x1e
[ 2059.881400]  [814762bf] ? _raw_spin_unlock_irqrestore+0x17/0x19
[ 2059.881404]  [8106953e] ? prepare_to_wait+0x6c/0x79
[ 2059.881419]  [a02e9764] 
btrfs_commit_transaction+0x2b2/0x665 [btrfs]

[ 2059.881423]  [810692ab] ? wake_up_bit+0x2a/0x2a
[ 2059.881440]  [a02f2d76] btrfs_write_inode+0x9b/0xa3 [btrfs]
[ 2059.881445]  [81138d78] writeback_single_inode+0x125/0x1bf
[ 2059.881450]  [81139055] writeback_sb_inodes+0xce/0x160
[ 2059.881454]  [81139d68] wb_writeback+0x257/0x3a7
[ 2059.881459]  [81139f40] wb_do_writeback+0x88/0x1a0
[ 2059.881464]  [8105b0a1] ? run_timer_softirq+0x298/0x298
[ 2059.881468]  [8113a0e3] bdi_writeback_thread+0x8b/0x20c
[ 2059.881473]  [8113a058] ? wb_do_writeback+0x1a0/0x1a0
[ 2059.881476]  [81068dce] kthread+0x82/0x8a
[ 2059.881481]  [8147db64] kernel_thread_helper+0x4/0x10
[ 2059.881485]  [81068d4c] ? kthread_worker_fn+0x14b/0x14b
[ 2059.881489]  [8147db60] ? gs_change+0x13/0x13
[ 2059.881493] fsstressD 8801a23f8000 0  2304  1 
0x0084
[ 2059.881497]  880189c93d48 0082  
0400
[ 2059.881502]  00013a80 00013a80 00013a80 
88017bc59710
[ 2059.881507]  00013a80 880189c93fd8 00013a80 
00013a80

[ 2059.881512] Call Trace:
[ 2059.881517]  [8103dadf] ? resched_task+0x48/0x72
[ 2059.881522]  [814750a4] schedule_timeout+0x36/0xe3
[