Messages in this thread | | | Date | Thu, 7 Sep 2006 14:35:13 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] fix /proc/partitions oops |
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On Thu, 7 Sep 2006 17:04:20 +0100 (BST) James Cross <james_cross@symantec.com> wrote:
> If show_partition happens to race with re-reading a partition table > (rescan_partitions), sgp->part[n] can become NULL just after it's been > tested, and so cause an oops: read it once (and read nr_sects just the > once too, to avoid a chance of showing 0). >
OK.
> > block/genhd.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > --- 2.6.18-rc6/block/genhd.c.orig 2006-09-07 12:14:32.183218000 +0100 > +++ 2.6.18-rc6/block/genhd.c 2006-09-07 12:15:16.134498000 +0100 > @@ -261,14 +261,18 @@ static int show_partition(struct seq_fil > (unsigned long long)get_capacity(sgp) >> 1, > disk_name(sgp, 0, buf)); > for (n = 0; n < sgp->minors - 1; n++) { > - if (!sgp->part[n]) > + struct hd_struct *partn; > + unsigned long long nr_sects; > + > + partn = sgp->part[n]; > + if (!partn) > continue; > - if (sgp->part[n]->nr_sects == 0) > + nr_sects = partn->nr_sects; > + if (nr_sects == 0) > continue; > seq_printf(part, "%4d %4d %10llu %s\n", > sgp->major, n + 1 + sgp->first_minor, > - (unsigned long long)sgp->part[n]->nr_sects >> 1 , > - disk_name(sgp, n + 1, buf)); > + nr_sects >> 1, disk_name(sgp, n + 1, buf)); > } > > return 0;
But that'll leave us reading possibly-freed memory.
I expect the correct way to fix this is with locking: the /proc/partitions reading code needs to lock down the partition information while it's reading it.
AFAICT the appropriate lock to take is the bdev->bd_mutex on the blockdev which represents the "whole" disk. But I'm not sure whether that's correct, nor what the official way is of hunting down that block_device*, nor whether the code in do_open() is managing to take the correct lock.
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