On Mon, 27 Feb 2012 15:11:35 -0800, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > 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. Viro explained the deadlock in detail here: http://mid.gmane.org/20120217002726.GL23916@xxxxxxxxxxxxxxxxxx I will also update the commit message with this information. > > 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? > Will update the patch with these details Thanks -aneesh -- 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>