linux-kernel - Re: [PATCHv3 02/10] ext4: Fix ext4_fc

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Date:   Thu, 17 Mar 2022 13:01:49 +0100
From:   Sven Schnelle <svens@...ux.ibm.com>
To:     Ritesh Harjani <riteshh@...ux.ibm.com>
Cc:     linux-ext4@...r.kernel.org, Jan Kara <jack@...e.cz>,
        "Theodore Ts'o" <tytso@....edu>,
        Harshad Shirwadkar <harshadshirwadkar@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...nel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCHv3 02/10] ext4: Fix ext4_fc_stats trace point

Ritesh Harjani <riteshh@...ux.ibm.com> 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@...nel.org
> Fixes: commit aa75f4d3daae ("ext4: main fast-commit commit path")
> Reported-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Ritesh Harjani <riteshh@...ux.ibm.com>
> Reviewed-by: Jan Kara <jack@...e.cz>
> Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> Reviewed-by: Harshad Shirwadkar <harshadshirwadkar@...il.com>
> ---
>  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
[    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
[    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