Re: [PATCHv3 02/10] ext4: Fix ext4_fc_stats trace point

From: Ritesh Harjani
Date: Thu Mar 17 2022 - 10:50:47 EST

On 22/03/17 01:01PM, Sven Schnelle wrote:
> Ritesh Harjani <riteshh@xxxxxxxxxxxxx> writes:
>
> > ftrace's __print_symbolic() requires that any enum values used in the
> > symbol to string translation table be wrapped in a TRACE_DEFINE_ENUM
> > so that the enum value can be decoded from the ftrace ring buffer by
> > user space tooling.
> >
> > This patch also fixes few other problems found in this trace point.
> > e.g. dereferencing structures in TP_printk which should not be done
> > at any cost.
> >
> > Also to avoid checkpatch warnings, this patch removes those
> > whitespaces/tab stops issues.
> >
> > Cc: stable@xxxxxxxxxx
> > Fixes: commit aa75f4d3daae ("ext4: main fast-commit commit path")
> > Reported-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
> > Reviewed-by: Jan Kara <jack@xxxxxxx>
> > Reviewed-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> > Reviewed-by: Harshad Shirwadkar <harshadshirwadkar@xxxxxxxxx>
> > ---
> > include/trace/events/ext4.h | 78 +++++++++++++++++++++++--------------
> > 1 file changed, 49 insertions(+), 29 deletions(-)
> >
> > diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
> > index 19e957b7f941..1a0b7030f72a 100644
> > --- a/include/trace/events/ext4.h
> > +++ b/include/trace/events/ext4.h
> > @@ -95,6 +95,17 @@ TRACE_DEFINE_ENUM(ES_REFERENCED_B);
> > { FALLOC_FL_COLLAPSE_RANGE, "COLLAPSE_RANGE"}, \
> > { FALLOC_FL_ZERO_RANGE, "ZERO_RANGE"})
> >
> > +TRACE_DEFINE_ENUM(EXT4_FC_REASON_XATTR);
> > +TRACE_DEFINE_ENUM(EXT4_FC_REASON_CROSS_RENAME);
> > +TRACE_DEFINE_ENUM(EXT4_FC_REASON_JOURNAL_FLAG_CHANGE);
> > +TRACE_DEFINE_ENUM(EXT4_FC_REASON_NOMEM);
> > +TRACE_DEFINE_ENUM(EXT4_FC_REASON_SWAP_BOOT);
> > +TRACE_DEFINE_ENUM(EXT4_FC_REASON_RESIZE);
> > +TRACE_DEFINE_ENUM(EXT4_FC_REASON_RENAME_DIR);
> > +TRACE_DEFINE_ENUM(EXT4_FC_REASON_FALLOC_RANGE);
> > +TRACE_DEFINE_ENUM(EXT4_FC_REASON_INODE_JOURNAL_DATA);
> > +TRACE_DEFINE_ENUM(EXT4_FC_REASON_MAX);
>
> I'm getting the following oops with that patch:
>
> [ 0.937455] VFS: Disk quotas dquot_6.6.0
> [ 0.937474] VFS: Dquot-cache hash table entries: 512 (order 0, 4096 bytes)
> [ 0.958347] Unable to handle kernel pointer dereference in virtual kernel address space
> [ 0.958350] Failing address: 00000000010de000 TEID: 00000000010de407
> [ 0.958353] Fault in home space mode while using kernel ASCE.
> [ 0.958357] AS:0000000001ed0007 R3:00000002ffff0007 S:0000000001003701
> [ 0.958388] Oops: 0004 ilc:3 [#1] SMP
> [ 0.958393] Modules linked in:
> [ 0.958398] CPU: 0 PID: 8 Comm: kworker/u128:0 Not tainted 5.17.0-rc8-next-20220317 #396

I tried running this master branch of linux-next from here [1].
But I started facing build failures with it.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git

> [ 0.958403] Hardware name: IBM 3906 M04 704 (z/VM 7.1.0)
> [ 0.958407] Workqueue: eval_map_wq eval_map_work_func
>
> [ 0.958446] Krnl PSW : 0704e00180000000 000000000090a9d6 (number+0x25e/0x3c0)
> [ 0.958456] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3
> [ 0.958461] Krnl GPRS: 0000000000000058 00000000010de0ac 0000000000000001 00000000fffffffc
> [ 0.958467] 0000038000047b80 0affffff010de0ab 0000000000000000 0000000000000000
> [ 0.958481] 0000000000000020 0000038000000000 00000000010de0ad 00000000010de0ab
> [ 0.958484] 0000000080312100 0000000000e68910 0000038000047b50 0000038000047ab8
> [ 0.958494] Krnl Code: 000000000090a9c6: f0c84112b001 srp 274(13,%r4),1(%r11),8
> [ 0.958494] 000000000090a9cc: 41202001 la %r2,1(%r2)
> [ 0.958494] #000000000090a9d0: ecab0006c065 clgrj %r10,%r11,12,000000000090a9dc
> [ 0.958494] >000000000090a9d6: d200b0004000 mvc 0(1,%r11),0(%r4)
> [ 0.958494] 000000000090a9dc: 41b0b001 la %r11,1(%r11)
> [ 0.958494] 000000000090a9e0: a74bffff
> aghi %r4,-1
> [ 0.958494] 000000000090a9e4: a727fff6 brctg %r2,000000000090a9d0
> [ 0.958494] 000000000090a9e8: a73affff ahi %r3,-1
> [ 0.958575] Call Trace:
> [ 0.958580] [<000000000090a9d6>] number+0x25e/0x3c0
> [ 0.958594] ([<0000000000289516>] update_event_printk+0xde/0x200)
> [ 0.958602] [<0000000000910020>] vsnprintf+0x4b0/0x7c8
> [ 0.958606] [<00000000009103e8>] snprintf+0x40/0x50
> [ 0.958610] [<00000000002893d2>] eval_replace+0x62/0xc8
> [ 0.958614] [<000000000028e2fe>] trace_event_eval_update+0x206/0x248

This looks like you must have this patch from Steven as well [2].
Although I did test the patch and didn't see such a crash on my qemu box [3].

[2]: https://lore.kernel.org/linux-ext4/20220310233234.4418186a@xxxxxxxxxxxxxxxxxx/
[3]: https://lore.kernel.org/linux-ext4/20220311051249.ltgqbjjothbrkbno@riteshh-domain/

@Steven,
Sorry to bother. But does this crash strike anything obvious to you?

-ritesh


> [ 0.958619] [<0000000000171bba>] process_one_work+0x1fa/0x460
> [ 0.958625] [<000000000017234c>] worker_thread+0x64/0x468
> [ 0.958629] [<000000000017af90>] kthread+0x108/0x110
> [ 0.958634] [<00000000001032ec>] __ret_from_fork+0x3c/0x58
> [ 0.958640] [<0000000000cce43a>] ret_from_fork+0xa/0x40
> [ 0.958648] Last Breaking-Event-Address:
> [ 0.958652] [<000000000090a99c>] number+0x224/0x3c0
> [ 0.958661] Kernel panic - not syncing: Fatal exception: panic_on_oops
>
> I haven't really checked what TRACE_DEFINE_ENUM() does, but removing the
> last line ("TRACE_DEFINE_ENUM(EXT4_FC_REASON_MAX);") makes the oops go
> away. Looking at all the other defines looks like the _MAX enum
> shouldn't be added there?
>
> Thanks
> Sven