On 01/06/2017 03:11 PM, Michal Hocko wrote: > From: Michal Hocko <mhocko@xxxxxxxx> > > The current implementation of the reclaim lockup detection can lead to > false positives and those even happen and usually lead to tweak the > code to silence the lockdep by using GFP_NOFS even though the context > can use __GFP_FS just fine. See > http://lkml.kernel.org/r/20160512080321.GA18496@dastard as an example. > > ================================= > [ INFO: inconsistent lock state ] > 4.5.0-rc2+ #4 Tainted: G O > --------------------------------- > inconsistent {RECLAIM_FS-ON-R} -> {IN-RECLAIM_FS-W} usage. > kswapd0/543 [HC0[0]:SC0[0]:HE1:SE1] takes: > > (&xfs_nondir_ilock_class){++++-+}, at: [<ffffffffa00781f7>] xfs_ilock+0x177/0x200 [xfs] > > {RECLAIM_FS-ON-R} state was registered at: > [<ffffffff8110f369>] mark_held_locks+0x79/0xa0 > [<ffffffff81113a43>] lockdep_trace_alloc+0xb3/0x100 > [<ffffffff81224623>] kmem_cache_alloc+0x33/0x230 > [<ffffffffa008acc1>] kmem_zone_alloc+0x81/0x120 [xfs] > [<ffffffffa005456e>] xfs_refcountbt_init_cursor+0x3e/0xa0 [xfs] > [<ffffffffa0053455>] __xfs_refcount_find_shared+0x75/0x580 [xfs] > [<ffffffffa00539e4>] xfs_refcount_find_shared+0x84/0xb0 [xfs] > [<ffffffffa005dcb8>] xfs_getbmap+0x608/0x8c0 [xfs] > [<ffffffffa007634b>] xfs_vn_fiemap+0xab/0xc0 [xfs] > [<ffffffff81244208>] do_vfs_ioctl+0x498/0x670 > [<ffffffff81244459>] SyS_ioctl+0x79/0x90 > [<ffffffff81847cd7>] entry_SYSCALL_64_fastpath+0x12/0x6f > > CPU0 > ---- > lock(&xfs_nondir_ilock_class); > <Interrupt> > lock(&xfs_nondir_ilock_class); > > *** DEADLOCK *** > > 3 locks held by kswapd0/543: > > stack backtrace: > CPU: 0 PID: 543 Comm: kswapd0 Tainted: G O 4.5.0-rc2+ #4 > > Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006 > > ffffffff82a34f10 ffff88003aa078d0 ffffffff813a14f9 ffff88003d8551c0 > ffff88003aa07920 ffffffff8110ec65 0000000000000000 0000000000000001 > ffff880000000001 000000000000000b 0000000000000008 ffff88003d855aa0 > Call Trace: > [<ffffffff813a14f9>] dump_stack+0x4b/0x72 > [<ffffffff8110ec65>] print_usage_bug+0x215/0x240 > [<ffffffff8110ee85>] mark_lock+0x1f5/0x660 > [<ffffffff8110e100>] ? print_shortest_lock_dependencies+0x1a0/0x1a0 > [<ffffffff811102e0>] __lock_acquire+0xa80/0x1e50 > [<ffffffff8122474e>] ? kmem_cache_alloc+0x15e/0x230 > [<ffffffffa008acc1>] ? kmem_zone_alloc+0x81/0x120 [xfs] > [<ffffffff811122e8>] lock_acquire+0xd8/0x1e0 > [<ffffffffa00781f7>] ? xfs_ilock+0x177/0x200 [xfs] > [<ffffffffa0083a70>] ? xfs_reflink_cancel_cow_range+0x150/0x300 [xfs] > [<ffffffff8110aace>] down_write_nested+0x5e/0xc0 > [<ffffffffa00781f7>] ? xfs_ilock+0x177/0x200 [xfs] > [<ffffffffa00781f7>] xfs_ilock+0x177/0x200 [xfs] > [<ffffffffa0083a70>] xfs_reflink_cancel_cow_range+0x150/0x300 [xfs] > [<ffffffffa0085bdc>] xfs_fs_evict_inode+0xdc/0x1e0 [xfs] > [<ffffffff8124d7d5>] evict+0xc5/0x190 > [<ffffffff8124d8d9>] dispose_list+0x39/0x60 > [<ffffffff8124eb2b>] prune_icache_sb+0x4b/0x60 > [<ffffffff8123317f>] super_cache_scan+0x14f/0x1a0 > [<ffffffff811e0d19>] shrink_slab.part.63.constprop.79+0x1e9/0x4e0 > [<ffffffff811e50ee>] shrink_zone+0x15e/0x170 > [<ffffffff811e5ef1>] kswapd+0x4f1/0xa80 > [<ffffffff811e5a00>] ? zone_reclaim+0x230/0x230 > [<ffffffff810e6882>] kthread+0xf2/0x110 > [<ffffffff810e6790>] ? kthread_create_on_node+0x220/0x220 > [<ffffffff8184803f>] ret_from_fork+0x3f/0x70 > [<ffffffff810e6790>] ? kthread_create_on_node+0x220/0x220 > > To quote Dave: > " > Ignoring whether reflink should be doing anything or not, that's a > "xfs_refcountbt_init_cursor() gets called both outside and inside > transactions" lockdep false positive case. The problem here is > lockdep has seen this allocation from within a transaction, hence a > GFP_NOFS allocation, and now it's seeing it in a GFP_KERNEL context. > Also note that we have an active reference to this inode. > > So, because the reclaim annotations overload the interrupt level > detections and it's seen the inode ilock been taken in reclaim > ("interrupt") context, this triggers a reclaim context warning where > it thinks it is unsafe to do this allocation in GFP_KERNEL context > holding the inode ilock... > " > > This sounds like a fundamental problem of the reclaim lock detection. > It is really impossible to annotate such a special usecase IMHO unless > the reclaim lockup detection is reworked completely. Until then it > is much better to provide a way to add "I know what I am doing flag" > and mark problematic places. This would prevent from abusing GFP_NOFS > flag which has a runtime effect even on configurations which have > lockdep disabled. > > Introduce __GFP_NOLOCKDEP flag which tells the lockdep gfp tracking to > skip the current allocation request. > > While we are at it also make sure that the radix tree doesn't > accidentaly override tags stored in the upper part of the gfp_mask. > > Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
