Hi,

I've just got this BUG: message in dmesg which I think is btrfs related.

I have a btrfs filesystem in a memory card which I use to contain the 
cache and config of chromium (to avoid writing to much in the SSD):

/dev/mmcblk0p1 on /home/mafra/mmc type btrfs (rw,noexec,nosuid,nodev,noatime,noacl,compress)

and the last message before the bug is about the memory card.

[  148.149179] mmcblk0: retrying using single block read
[  148.152014] BUG: unable to handle kernel NULL pointer dereference at (null)
[  148.152021] IP: [<ffffffff811b1301>] extent_range_uptodate+0x51/0xa0
[  148.152030] PGD 72c37067 PUD 7d64b067 PMD 0 
[  148.152035] Oops: 0000 [#1] SMP 
[  148.152038] last sysfs file: /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
[  148.152041] CPU 1 
[  148.152043] Modules linked in: snd_seq snd_seq_device snd_hda_codec_idt i2c_i801 snd_hda_intel snd_hda_codec sky2 uvcvideo iwlagn snd_hwdep evdev
[  148.152053] 
[  148.152057] Pid: 2731, comm: btrfs-endio-met Not tainted 2.6.35.3+ #12 VAIO/VGN-FZ240E
[  148.152059] RIP: 0010:[<ffffffff811b1301>]  [<ffffffff811b1301>] extent_range_uptodate+0x51/0xa0
[  148.152064] RSP: 0018:ffff880079acddd0  EFLAGS: 00010246
[  148.152066] RAX: 0000000000000000 RBX: 0000000043eba000 RCX: 0000000000000000
[  148.152068] RDX: 0000000000000001 RSI: 0000000000043eba RDI: 0000000000000001
[  148.152071] RBP: ffff880079acddf0 R08: 0000000000000000 R09: 0000000000000000
[  148.152073] R10: 0000000000001000 R11: 0000000000000000 R12: ffff88007b40eb18
[  148.152076] R13: 0000000043ebadff R14: ffff880079ab0000 R15: ffff880079acde80
[  148.152079] FS:  0000000000000000(0000) GS:ffff880001b00000(0000) knlGS:0000000000000000
[  148.152081] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  148.152084] CR2: 0000000000000000 CR3: 0000000070be9000 CR4: 00000000000006e0
[  148.152086] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  148.152088] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[  148.152091] ...
[ message continues ]

Hmmm it is definitely btrfs related.  Do you continue to get it after
rebooting?

-chris
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[ message continues ]

No, after rebooting chromium refused to open (like it did during the BUG) 
but no BUG: message appeared.

Then I deleted all chromium cache+config from the memory card and chromium
worked again, but after suspending to RAM I noticed this:

[ 6035.423238] PM: Syncing filesystems ... done.
[ 6036.524889] Freezing user space processes ... 
[ 6056.533079] Freezing of tasks failed after 20.00 seconds (1 tasks refusing to freeze):
[ 6056.533119] chrome        D 00000000ffffffff     0  7028   7015 0x00800004
[ 6056.533124]  ffff8800630a1c08 0000000000000086 0000000000000000 0000000000012d40
[ 6056.533129]  ffff8800630a1fd8 ffff8800630a1fd8 ffff88006303e0c0 0000000000012d40
[ 6056.533133]  0000000000012d40 0000000000004000 0000000000004000 ffff8800630a1fd8
[ 6056.533137] Call Trace:
[ 6056.533145]  [<ffffffff81064029>] ? ktime_get_ts+0xa9/0xe0
[ 6056.533150]  [<ffffffff810a3610>] ? sync_page_killable+0x0/0x40
[ 6056.533155]  [<ffffffff81506bde>] io_schedule+0x6e/0xb0
[ 6056.533158]  [<ffffffff810a35f8>] sync_page+0x38/0x50
[ 6056.533161]  [<ffffffff810a3619>] sync_page_killable+0x9/0x40
[ 6056.533164]  [<ffffffff81507332>] __wait_on_bit_lock+0x52/0xb0
[ 6056.533168]  [<ffffffff810a3532>] __lock_page_killable+0x62/0x70
[ 6056.533172]  [<ffffffff8105bb40>] ? wake_bit_function+0x0/0x40
[ 6056.533175]  [<ffffffff810a3459>] ? find_get_page+0x19/0x90
[ 6056.533178]  [<ffffffff810a5144>] generic_file_aio_read+0x494/0x6d0
[ 6056.533183]  [<ffffffff810d4b22>] do_sync_read+0xd2/0x110
[ 6056.533186]  [<ffffffff81025406>] ? do_page_fault+0x186/0x390
[ 6056.533190]  [<ffffffff810d5273>] vfs_read+0xb3/0x160
[ 6056.533193]  [<ffffffff810d536c>] sys_read+0x4c/0x80
[ 6056.533197]  [<ffffffff81002d2b>] system_call_fastpath+0x16/0x1b
[ 6056.533207] 
[ 6056.533208] Restarting tasks ... done.

but everything is working well AFAICT.
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[ message continues ]

Hi, Carlos,
Did you hit this bug under heavy memory stress?

And, could you reproduce the bug? or show some reproduce steps for us?

After digging into extent_range_uptodate(), IMO, this NULL pointer bug that issued page 
can barely be hit. 

Maybe, due to heavy memory stress, a page of the extent_buffer has been freed before, 
which leads that it is missing in page_cache and return NULL.


thanks,

--

[ message continues ]

Not at all! 

My laptop had been recently booted (see the timings in the dmesg)
and it was basically idle: just a couple xterms and WindowMaker running,


Could it be that the memory card had some bad block and btrfs could not
recover from the failure?

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