On Sun, 26 Feb 2012 23:49:58 +0530 "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote: > From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> > > Drop using inode->i_mutex from read, since that can result in deadlock with > mmap. Ideally we can extend the patch to make sure we don't increase i_size > in mmap. But that will break userspace, because application will have to now > use truncate(2) to increase i_size in hugetlbfs. > > AFAIU i_mutex was added in hugetlbfs_read as per > http://lkml.indiana.edu/hypermail/linux/kernel/0707.2/3066.html This patch comes somewhat out of the blue and I'm unsure what's going on. You say there's some (potential?) deadlock with mmap, but it is undescribed. Have people observed this deadlock? Has it caused lockdep warnings? Please update the changelog to fully describe the bug. Also, the new truncate_sem is undoumented. This leaves readers to work out for themselves what it might be for. Please let's add code comments which completely describe the race, and how this lock prevents it. We should also document our locking rules. When should code take this lock? What are its ranking rules with respect to i_mutex, i_mmap_mutex and possibly others? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>