Messages in this thread | | | Date | Mon, 14 Jan 2008 03:43:23 +0000 | From | Al Viro <> | Subject | Re: [PATCH 002 of 6] md: Fix use-after-free bug when dropping an rdev from an md array. |
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On Mon, Jan 14, 2008 at 02:21:45PM +1100, Neil Brown wrote:
> Maybe it isn't there any more.... > > Once upon a time, when I > echo remove > /sys/block/mdX/md/dev-YYY/state
Egads. And just what will protect you from parallel callers of state_store()? buffer->mutex does *not* do that - it only gives you exclusion on given struct file. Run the command above from several shells and you've got independent open from each redirect => different struct file *and* different buffer for each => no exclusion whatsoever.
And _that_ is present right in the mainline tree - it's unrelated to -mm kobject changes.
BTW, yes, you do have a deadlock there - kobject_del() will try to evict children, which will include waiting for currently running ->store() to finish, which will include the caller since .../state *is* a child of that sucker.
The real problem is the lack of any kind of exclusion considerations in md.c itself, AFAICS. Fun with ordering is secondary (BTW, yes, it is a problem - will sysfs ->store() to attribute between export_rdev() and kobject_del() work correctly?)
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