On Sat, Jul 03, 2010 at 10:43:23AM +0100, Al Viro wrote: > On Sat, Jul 03, 2010 at 10:24:42AM +0100, Al Viro wrote: > > > Gyah... For the 1001st time: readdir() is far from being the only thing that > > nests mmap_sem inside i_mutex. In particular, write() does the same thing. > > > > So yes, it *is* a real deadlock, TYVM, with no directories involved. Open the > > same file twice, mmap one fd, close it, then have munmap() hitting i_mutex > > in reiserfs_file_release() race with write() through another fd. > > > > Incidentally, reiserfs_file_release() checks in the fastpath look completely > > bogus. Checking i_count? What the hell is that one about? And no, these > > checks won't stop open() coming between them and grabbing i_mutex, so they > > couldn't prevent the deadlock in question anyway. > > ... and unfortunately it's been that way since the the initial merge in 2.4.early. > FWIW, it seems that i_count check was a misguided attempt to check that no other > opened struct file are there, but it's > a) wrong, since way, _way_ back - open() affects d_count, not i_count > b) wrong even with such modification (consider hardlinks) > c) wrong for even more reasons since forever - i_count and d_count could > be bumped by many things at any time > d) hopelessly racy anyway, since another open() could very well have > happened just as we'd finished these checks. OK... See 22093b8f3d387f77 in vfs-2.6.git for-next (should propagate to git.kernel.org shortly). That ought to deal with this crap, assuming I hadn't fucked up somewhere... -- To unsubscribe from this list: send the line "unsubscribe reiserfs-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
