Messages in this thread | | | Subject | Re: [PATCH 01/17] MTD: create lockless versions of {get,put}_mtd_device This will be used to resolve deadlock in block translation layer. | From | Maxim Levitsky <> | Date | Tue, 09 Feb 2010 19:46:14 +0200 |
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On Tue, 2010-02-09 at 19:23 +0200, Maxim Levitsky wrote: > On Tue, 2010-02-09 at 18:14 +0100, Peter Zijlstra wrote: > > On Tue, 2010-02-09 at 18:57 +0200, Maxim Levitsky wrote: > > > These functions can be used as long as we don't need access to global mtd table, but have > > > a pointer to the mtd device. > > > > > > Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com> > > > --- > > > drivers/mtd/mtdcore.c | 60 ++++++++++++++++++++++++++++++---------------- > > > include/linux/mtd/mtd.h | 3 +- > > > 2 files changed, 41 insertions(+), 22 deletions(-) > > > > > +int __get_mtd_device(struct mtd_info *mtd) > > > +{ > > > + int err; > > > + > > > + if (!try_module_get(mtd->owner)) > > > + return -ENODEV; > > > + > > > + if (mtd->get_device) { > > > + > > > + err = mtd->get_device(mtd); > > > + > > > + if (err) { > > > + module_put(mtd->owner); > > > + return err; > > > + } > > > + } > > > + mtd->usecount++; > > > + return 0; > > > } > > > > > +void __put_mtd_device(struct mtd_info *mtd) > > > +{ > > > + --mtd->usecount; > > > + BUG_ON(mtd->usecount < 0); > > > + > > > if (mtd->put_device) > > > mtd->put_device(mtd); > > > > > > module_put(mtd->owner); > > > } > > > > That's racy, use kref. > > > Couldn't agree with you more. > > However, these functions aren't intended for general use, and probably > will be used by mtd translation layer only. I do have a lock that > protects concurrent use of these functions. > > Thus, I better add a comment about this? However on second thought, there is still a race if two FTLs access same mtd device. While this might seem impossible, and I say it is quite dangerous. I can imagine using both some FTL and mtdblock for testing.
Just using kref (nothing against it) won't help here. The mtd->get_device/put_device aren't expecting to be called concurrently ether...
I can add per mtd lock, but it is a bit ugly...
What do you think?
Best regards, Maxim Levitsky
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