Messages in this thread | | | Date | Wed, 2 Jun 2010 09:02:40 +0800 | Subject | Re: [PATCH] fs: run emergency remount on dedicated workqueue | From | Dave Young <> |
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On Wed, Jun 2, 2010 at 7:46 AM, Andrew Morton <akpm@linux-foundation.org> wrote: > On Thu, 27 May 2010 11:57:23 +0200 > Tejun Heo <tj@kernel.org> wrote: > >> Commit fa4b9074cd8428958c2adf9dc0c831f46e27c193 made s_umount depend >> on keventd; > > For a while I thought you had the wrong commit ID, but I worked it out! > > Please, always quote the patch title rather than a bare commit ID. The > usual form is > > fa4b9074cd8428958c2adf9dc0c831f46e27c193 ("buffer: make > invalidate_bdev() drain all percpu LRU add caches:) > > The main reason for this is so that people can more reliably and simply > identify the patch within a different tree. I think. > >> however, emergency remount schedules works to keventd >> which grabs s_umount creating a circular dependency. Run emergency >> remount on a separate workqueue to break it. >> >> ... >> >> index 69688b1..1ada607 100644 >> --- a/fs/super.c >> +++ b/fs/super.c >> @@ -575,6 +575,11 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force) >> return 0; >> } >> >> +/* >> + * For emergency remount >> + */ >> +static struct workqueue_struct *emergency_remount_wq; >> + >> static void do_emergency_remount(struct work_struct *work) >> { >> struct super_block *sb, *n; >> @@ -605,13 +610,25 @@ void emergency_remount(void) >> { >> struct work_struct *work; >> >> + if (!emergency_remount_wq) >> + return; >> + >> work = kmalloc(sizeof(*work), GFP_ATOMIC); >> if (work) { >> INIT_WORK(work, do_emergency_remount); >> - schedule_work(work); >> + queue_work(emergency_remount_wq, work); >> } >> } >> >> +static int __init emergency_remount_init(void) >> +{ >> + emergency_remount_wq = create_singlethread_workqueue("emerg-remount"); >> + if (!emergency_remount_wq) >> + pr_warn("failed to create emergency remount workqueue\n"); >> + return 0; >> +} >> +subsys_initcall(emergency_remount_init); >> + >> /* >> * Unnamed block devices are dummy devices used by virtual >> * filesystems which don't use real block-devices. -- jrs > > gaah. Do we really want to add Yet Another Kernel Thread just for that > dopey sysrq-U thing? > > I assume (coz you didn't tell us) that it generates a lockdep spew? > Perhaps it'd be better to just suppress that somehow rather than this... > > And if we _do_ end up adding a new kernel thread for this, maybe it > would be better to use that thread for lru_add_drain_all() rather than > within the dopey do_emergency_remount(), so as to reduce the likelihood > that we'll need to add even more kernel threads to solve the same > problem elsewhere? But this would require a new kernel thread on each > CPU, grr. > > Another possibility might be to change lru_add_drain_all() to use IPI > interrupts rather than schedule_on_each_cpu(). That would greatly > speed up lru_add_drain_all(). I don't recall why we did it that way > and I don't immediately see a reason not to. A few things in core mm > would need to be changed from spin_lock_irq() to spin_lock_irqsave(). > > But I do have vague memories that there was a reason for it. > > <It's a huge PITA locating the commit which initially added > lru_add_drain_all()> > > <ten minutes later> > > : tree 05d7615894131a368fc4943f641b11acdd2ae694 > : parent e236a166b2bc437769a9b8b5d19186a3761bde48 > : author Nick Piggin <npiggin@suse.de> Thu, 19 Jan 2006 09:42:27 -0800 > : committer Linus Torvalds <torvalds@g5.osdl.org> Thu, 19 Jan 2006 11:20:17 -0800 > : > : [PATCH] mm: migration page refcounting fix > : > : Migration code currently does not take a reference to target page > : properly, so between unlocking the pte and trying to take a new > : reference to the page with isolate_lru_page, anything could happen to > : it. > : > : Fix this by holding the pte lock until we get a chance to elevate the > : refcount. > : > : Other small cleanups while we're here. > > It didn't tell us. > > <looks in the linux-mm archives> > > Nope, no rationale is provided there either.
Maybe this thread?
http://lkml.org/lkml/2008/10/23/226
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-- Regards dave -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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