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Date: Mon, 1 Mar 2021 19:07:41 +0100
From: Petr Mladek <pmladek@...e.com>
To: John Ogness <john.ogness@...utronix.de>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
linux-kernel@...r.kernel.org,
Michael Ellerman <mpe@...erman.id.au>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Jeff Dike <jdike@...toit.com>,
Richard Weinberger <richard@....at>,
Anton Ivanov <anton.ivanov@...bridgegreys.com>,
"K. Y. Srinivasan" <kys@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
Stephen Hemminger <sthemmin@...rosoft.com>,
Wei Liu <wei.liu@...nel.org>,
Miquel Raynal <miquel.raynal@...tlin.com>,
Vignesh Raghavendra <vigneshr@...com>,
Kees Cook <keescook@...omium.org>,
Anton Vorontsov <anton@...msg.org>,
Colin Cross <ccross@...roid.com>,
Tony Luck <tony.luck@...el.com>,
Jason Wessel <jason.wessel@...driver.com>,
Daniel Thompson <daniel.thompson@...aro.org>,
Douglas Anderson <dianders@...omium.org>,
Pavel Tatashin <pasha.tatashin@...een.com>,
Joel Stanley <joel@....id.au>,
Christophe Leroy <christophe.leroy@....fr>,
Jordan Niethe <jniethe5@...il.com>,
Alistair Popple <alistair@...ple.id.au>,
Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
Nicholas Piggin <npiggin@...il.com>,
Mike Rapoport <rppt@...nel.org>,
Madhavan Srinivasan <maddy@...ux.ibm.com>,
Thomas Meyer <thomas@...3r.de>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Davidlohr Bueso <dave@...olabs.net>,
Oleg Nesterov <oleg@...hat.com>, Wei Li <liwei391@...wei.com>,
Michael Kelley <mikelley@...rosoft.com>,
linuxppc-dev@...ts.ozlabs.org, linux-um@...ts.infradead.org,
linux-hyperv@...r.kernel.org, linux-mtd@...ts.infradead.org,
kgdb-bugreport@...ts.sourceforge.net
Subject: Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator
On Thu 2021-02-25 21:24:35, John Ogness wrote:
> Rather than storing the iterator information in the registered
> kmsg_dumper structure, create a separate iterator structure. The
> kmsg_dump_iter structure can reside on the stack of the caller, thus
> allowing lockless use of the kmsg_dump functions.
>
> This change also means that the kmsg_dumper dump() callback no
> longer needs to pass in the kmsg_dumper as an argument. If
> kmsg_dumpers want to access the kernel logs, they can use the new
> iterator.
>
> Update the kmsg_dumper callback prototype. Update code that accesses
> the kernel logs using the kmsg_dumper structure to use the new
> kmsg_dump_iter structure. For kmsg_dumpers, this also means adding a
> call to kmsg_dump_rewind() to initialize the iterator.
>
> All this is in preparation for removal of @logbuf_lock.
>
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> ---
> arch/powerpc/kernel/nvram_64.c | 14 +++---
> arch/powerpc/platforms/powernv/opal-kmsg.c | 3 +-
> arch/powerpc/xmon/xmon.c | 6 +--
> arch/um/kernel/kmsg_dump.c | 8 +--
> drivers/hv/vmbus_drv.c | 7 +--
> drivers/mtd/mtdoops.c | 8 +--
> fs/pstore/platform.c | 8 +--
> include/linux/kmsg_dump.h | 38 ++++++++-------
> kernel/debug/kdb/kdb_main.c | 10 ++--
> kernel/printk/printk.c | 57 ++++++++++------------
> 10 files changed, 81 insertions(+), 78 deletions(-)
>
> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
> index 532f22637783..5a64b24a91c2 100644
> --- a/arch/powerpc/kernel/nvram_64.c
> +++ b/arch/powerpc/kernel/nvram_64.c
> @@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
> NULL
> };
>
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> - enum kmsg_dump_reason reason);
> +static void oops_to_nvram(enum kmsg_dump_reason reason);
>
> static struct kmsg_dumper nvram_kmsg_dumper = {
> .dump = oops_to_nvram
> @@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
> * that we think will compress sufficiently to fit in the lnx,oops-log
> * partition. If that's too much, go back and capture uncompressed text.
> */
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> - enum kmsg_dump_reason reason)
> +static void oops_to_nvram(enum kmsg_dump_reason reason)
> {
> struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
> static unsigned int oops_count = 0;
> + static struct kmsg_dump_iter iter;
> static bool panicking = false;
> static DEFINE_SPINLOCK(lock);
> unsigned long flags;
> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
> return;
>
> if (big_oops_buf) {
> - kmsg_dump_get_buffer(dumper, false,
> + kmsg_dump_rewind(&iter);
It would be nice to get rid of the kmsg_dump_rewind(&iter) calls
in all callers.
A solution might be to create the following in include/linux/kmsg_dump.h
#define KMSG_DUMP_ITER_INIT(iter) { \
.cur_seq = 0, \
.next_seq = U64_MAX, \
}
#define DEFINE_KMSG_DUMP_ITER(iter) \
struct kmsg_dump_iter iter = KMSG_DUMP_ITER_INIT(iter)
Then we could do the following at the beginning of both
kmsg_dump_get_buffer() and kmsg_dump_get_line():
u64 clear_seq = latched_seq_read_nolock(&clear_seq);
if (iter->cur_seq < clear_seq)
cur_seq = clear_seq;
I am not completely sure about next_seq:
+ kmsg_dump_get_buffer() will set it for the next call anyway.
It reads the blocks of messages from the newest.
+ kmsg_dump_get_line() wants to read the entire buffer anyway.
But there is a small risk of an infinite loop when new messages
are printed when dumping each line.
It might be better to avoid the infinite loop. We could do the following:
static void check_and_set_iter(struct kmsg_dump_iter)
{
if (iter->cur_seq == 0 && iter->next_seq == U64_MAX) {
kmsg_dump_rewind(iter);
}
and call this at the beginning of both kmsg_dump_get_buffer()
and kmsg_dump_get_line()
What do you think?
Note that I do not resist on it. But it might make the API easier to
use from my POV.
Otherwise the patch looks good to me.
Best Regards,
Petr
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