* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=16129 > > Subject : BUG: using smp_processor_id() in preemptible [00000000] code: jbd2/sda2 > > Submitter : Jan Kreuzer <kontrollator@xxxxxx> > > Date : 2010-06-05 06:15 (4 days old) > > This seems to have been introduced by > > commit 7cbaef9c83e58bbd4bdd534b09052b6c5ec457d5 > Author: Ingo Molnar <mingo@xxxxxxx> > Date: Sat Nov 8 17:05:38 2008 +0100 > > sched: optimize sched_clock() a bit > > sched_clock() uses cycles_2_ns() needlessly - which is an irq-disabling > variant of __cycles_2_ns(). > > Most of the time sched_clock() is called with irqs disabled already. > The few places that call it with irqs enabled need to be updated. > > Signed-off-by: Ingo Molnar <mingo@xxxxxxx> > > and this seems to be one of those calling cases that need to be updated. That's a commit from 2008. > Ingo? The call trace is: > > BUG: using smp_processor_id() in preemptible [00000000] code: jbd2/sda2-8/337 > caller is native_sched_clock+0x3c/0x68 > Pid: 337, comm: jbd2/sda2-8 Not tainted 2.6.35-rc1jan+ #4 > Call Trace: > [<ffffffff812362c5>] debug_smp_processor_id+0xc9/0xe4 > [<ffffffff8101059d>] native_sched_clock+0x3c/0x68 > [<ffffffff8101043d>] sched_clock+0x9/0xd > [<ffffffff81212d7a>] blk_rq_init+0x97/0xa3 > [<ffffffff81214d71>] get_request+0x1c4/0x2d0 > [<ffffffff81214ea6>] get_request_wait+0x29/0x1a6 > [<ffffffff81215537>] __make_request+0x338/0x45b > [<ffffffff812147c2>] generic_make_request+0x2bb/0x330 > [<ffffffff81214909>] submit_bio+0xd2/0xef > [<ffffffff811413cb>] submit_bh+0xf4/0x116 > [<ffffffff81144853>] block_write_full_page_endio+0x89/0x96 > [<ffffffff81144875>] block_write_full_page+0x15/0x17 > [<ffffffff8119b00a>] ext4_writepage+0x356/0x36b > [<ffffffff810e1f91>] __writepage+0x1a/0x39 > [<ffffffff810e32a6>] write_cache_pages+0x20d/0x346 > [<ffffffff810e3406>] generic_writepages+0x27/0x29 > [<ffffffff811ca279>] journal_submit_data_buffers+0x110/0x17d > [<ffffffff811ca986>] jbd2_journal_commit_transaction+0x4cb/0x156d > [<ffffffff811d0cba>] kjournald2+0x147/0x37a > > (from the bugzilla thing) The warning was introduced by this fresh commit (and a followup commit) merged in the .35 merge window: | commit 9195291e5f05e01d67f9a09c756b8aca8f009089 | Author: Divyesh Shah <dpshah@xxxxxxxxxx> | Date: Thu Apr 1 15:01:41 2010 -0700 | | blkio: Increment the blkio cgroup stats for real now IIRC Jens posted a fix for the regression. Jens, what's the status of that? As the code there started using a raw sched_clock() call for block statistics purposes, which was a poorly thought out (and buggy) approach: - it takes timestamps on different cpus and then compares then, but doesnt consider that sched_clock() is not comparable between CPUs without extra care - it doesnt consider the possibility for the sched_clock() result going backwards on certain platforms (such as x86) - it doesnt consider preemptability (There's work ongoing to add a clock variant that can be used for such purposes, but that's .36 fodder.) Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
