On Tue 01-11-16 23:17:33, Ross Zwisler wrote: > On Tue, Nov 01, 2016 at 11:36:06PM +0100, Jan Kara wrote: > > Hello, > > > > this is the fourth revision of my patches to clear dirty bits from radix tree > > of DAX inodes when caches for corresponding pfns have been flushed. This patch > > set is significantly larger than the previous version because I'm changing how > > ->fault, ->page_mkwrite, and ->pfn_mkwrite handlers may choose to handle the > > fault so that we don't have to leak details about DAX locking into the generic > > code. In principle, these patches enable handlers to easily update PTEs and do > > other work necessary to finish the fault without duplicating the functionality > > present in the generic code. I'd be really like feedback from mm folks whether > > such changes to fault handling code are fine or what they'd do differently. > > > > The patches are based on 4.9-rc1 + Ross' DAX PMD page fault series [1] + ext4 > > conversion of DAX IO patch to the iomap infrastructure [2]. For testing, > > I've pushed out a tree including all these patches and further DAX fixes > > to: > > > > git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs.git dax > > In my testing I hit what I believe to be a new lockdep splat. This was > produced with ext4+dax+generic/246, though I've tried several times to > reproduce it and haven't been able. This testing was done with your tree plus > one patch to fix the DAX PMD recursive fallback issue that you reported. This > new patch is folded into v9 of my PMD series that I sent out earlier today. > > I've posted the tree I was testing with here: > > https://git.kernel.org/cgit/linux/kernel/git/zwisler/linux.git/log/?h=jan_dax > > Here is the lockdep splat, passed through kasan_symbolize: > > run fstests generic/246 at 2016-11-01 21:51:34 > > ====================================================== > [ INFO: possible circular locking dependency detected ] > 4.9.0-rc1-00165-g13826b5 #2 Not tainted > ------------------------------------------------------- > t_mmap_writev/13704 is trying to acquire lock: > ([ 3522.320075] &ei->i_mmap_sem > ){++++.+}[ 3522.320924] , at: > [<ffffffff8133ef06>] ext4_dax_fault+0x36/0xd0 fs/ext4/file.c:267 Interesting, I didn't see this in my testing. > -> #0[ 3522.342547] ( > &ei->i_mmap_sem[ 3522.343023] ){++++.+} > : > [< inline >] check_prev_add kernel/locking/lockdep.c:1829 > [< inline >] check_prevs_add kernel/locking/lockdep.c:1939 > [< inline >] validate_chain kernel/locking/lockdep.c:2266 > [<ffffffff8110e89f>] __lock_acquire+0x127f/0x14d0 kernel/locking/lockdep.c:3335 > [<ffffffff8110efa2>] lock_acquire+0xf2/0x1e0 kernel/locking/lockdep.c:3746 > [<ffffffff81b39b7e>] down_read+0x3e/0xa0 kernel/locking/rwsem.c:22 > [<ffffffff8133ef06>] ext4_dax_fault+0x36/0xd0 fs/ext4/file.c:267 > [<ffffffff8122f9d1>] __do_fault+0x21/0x130 mm/memory.c:2872 > [< inline >] do_read_fault mm/memory.c:3231 > [< inline >] do_fault mm/memory.c:3333 > [< inline >] handle_pte_fault mm/memory.c:3534 > [< inline >] __handle_mm_fault mm/memory.c:3624 > [<ffffffff812348ae>] handle_mm_fault+0x114e/0x1550 mm/memory.c:3661 > [<ffffffff8106bc27>] __do_page_fault+0x247/0x4f0 arch/x86/mm/fault.c:1397 > [<ffffffff8106bfad>] trace_do_page_fault+0x5d/0x290 arch/x86/mm/fault.c:1490 > [<ffffffff81065dba>] do_async_page_fault+0x1a/0xa0 arch/x86/kernel/kvm.c:265 > [<ffffffff81b3ea08>] async_page_fault+0x28/0x30 arch/x86/entry/entry_64.S:1015 > [< inline >] arch_copy_from_iter_pmem ./arch/x86/include/asm/pmem.h:95 > [< inline >] copy_from_iter_pmem ./include/linux/pmem.h:118 > [<ffffffff812f4a27>] dax_iomap_actor+0x147/0x270 fs/dax.c:1027 > [<ffffffff8130c513>] iomap_apply+0xb3/0x130 fs/iomap.c:78 So the problem is that we were doing write to a DAX file from a buffer which is mmapped DAX file and we took a fault when copying data from the buffer. That looks like a real problem. I'll have to think what to do with it... Thanks for report! > [<ffffffff812f46d6>] dax_iomap_rw+0x76/0xa0 fs/dax.c:1067 > [< inline >] ext4_dax_write_iter fs/ext4/file.c:196 > [<ffffffff8133fb13>] ext4_file_write_iter+0x243/0x340 fs/ext4/file.c:217 > [<ffffffff812957d1>] do_iter_readv_writev+0xb1/0x130 fs/read_write.c:695 > [<ffffffff81296384>] do_readv_writev+0x1a4/0x250 fs/read_write.c:872 > [<ffffffff8129668f>] vfs_writev+0x3f/0x50 fs/read_write.c:911 > [<ffffffff81296704>] do_writev+0x64/0x100 fs/read_write.c:944 > [< inline >] SYSC_writev fs/read_write.c:1017 > [<ffffffff81297900>] SyS_writev+0x10/0x20 fs/read_write.c:1014 > [<ffffffff81b3d501>] entry_SYSCALL_64_fastpath+0x1f/0xc2 arch/x86/entry/entry_64.S:209 > Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>