[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20100524140002.GA11816@atrey.karlin.mff.cuni.cz>
Date: Mon, 24 May 2010 16:00:02 +0200
From: Jan Kara <jack@...e.cz>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Rafael J. Wysocki" <rjw@...k.pl>,
LKML <linux-kernel@...r.kernel.org>,
Al Viro <viro@...iv.linux.org.uk>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Eric Paris <eparis@...hat.com>,
Dmitry Monakhov <dmonakhov@...nvz.org>, Jan Kara <jack@....cz>
Subject: Re: [git head f4b87dee9] BUG: using smp_processor_id() in
preemptible (VFS-related)
Hi,
> On Sat, 22 May 2010 23:36:59 +0200 "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> > [ 6.906133] EXT4-fs (sda7): mounted filesystem with ordered data mode
> > [ 7.014359] BUG: using smp_processor_id() in preemptible [00000000] code: mount/1501
> > [ 7.020570] caller is dqstats_inc+0x19/0x2c
> > [ 7.026658] Pid: 1501, comm: mount Not tainted 2.6.34-tst #25
> > [ 7.032792] Call Trace:
> > [ 7.038859] [<ffffffff8117c12b>] debug_smp_processor_id+0xcb/0xdc
> > [ 7.045025] [<ffffffff8111dfb5>] dqstats_inc+0x19/0x2c
> > [ 7.051201] [<ffffffff81120fac>] vfs_quota_sync+0x144/0x210
> > [ 7.057349] [<ffffffff810eccfa>] ? __shrink_dcache_sb+0x284/0x293
> > [ 7.063574] [<ffffffff810fc48d>] __sync_filesystem+0x3a/0x7e
> > [ 7.069730] [<ffffffff810fc552>] sync_filesystem+0x36/0x4c
> > [ 7.075867] [<ffffffff810deef0>] do_remount_sb+0x65/0x13c
> > [ 7.081960] [<ffffffff810f4359>] do_mount+0x251/0x78a
> > [ 7.088039] [<ffffffff810f2c3e>] ? copy_mount_options+0xda/0x146
> > [ 7.094086] [<ffffffff810f4911>] sys_mount+0x7f/0xb8
> > [ 7.100085] [<ffffffff81002aeb>] system_call_fastpath+0x16/0x1b
> > [ 7.124208] BUG: using smp_processor_id() in preemptible [00000000] code: mount/1501
> > [ 7.130307] caller is dqstats_inc+0x19/0x2c
> > [ 7.136386] Pid: 1501, comm: mount Not tainted 2.6.34-tst #25
> > [ 7.142512] Call Trace:
> > [ 7.148629] [<ffffffff8117c12b>] debug_smp_processor_id+0xcb/0xdc
> > [ 7.154846] [<ffffffff8111dfb5>] dqstats_inc+0x19/0x2c
> > [ 7.161019] [<ffffffff81120fac>] vfs_quota_sync+0x144/0x210
> > [ 7.167171] [<ffffffff810fc48d>] __sync_filesystem+0x3a/0x7e
> > [ 7.173364] [<ffffffff810fc563>] sync_filesystem+0x47/0x4c
> > [ 7.179522] [<ffffffff810deef0>] do_remount_sb+0x65/0x13c
> > [ 7.185616] [<ffffffff810f4359>] do_mount+0x251/0x78a
> > [ 7.191663] [<ffffffff810f2c3e>] ? copy_mount_options+0xda/0x146
> > [ 7.197626] [<ffffffff810f4911>] sys_mount+0x7f/0xb8
> > [ 7.203493] [<ffffffff81002aeb>] system_call_fastpath+0x16/0x1b
> > [ 11.643596] udev: starting version 153
> >
> > This is after reverting commit a7cf4145b (anon_inode: set S_IFREG on the
> > anon_inode) that the system is not really useable with.
>
> Caused by "quota: Make quota stat accounting lockless".
>
> Guys, the code this patch adds utterly duplicates the interface
> provided by include/linux/percpu_counter.h, only the quota code does it
> wrongly and badly. Please, can we use the nice library code?
I was thinking about this when merging the code and I thought that I'll save
some memory (~200 bytes) because stats are fine with 32-bit counters (instead of
64-bit ones) and I'm interested only in rough counts, not exact ones. Since the
code Dmitry added was quite simple, I thought the duplication won't be so bad.
But the code is probably more subtle than I thought so those 200 bytes aren't
worth it. So let's convert it to generic per-cpu counters. Dmitry, will you do it?
Hmm, I'm also wondering why I didn't see the warning Rafael was hitting in my
test runs... Ah, my kernel config has CONFIG_PREEMPT_NONE! I guess using
CONFIG_PREEMPT is likely to give a better test coverage, right?
Honza
--
Jan Kara <jack@...e.cz>
SuSE CR Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists