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> --- include/linux/gfp.h | 10 +++++++++- kernel/locking/lockdep.c | 4 ++++ lib/radix-tree.c | 2 ++ 3 files changed, 15 insertions(+), 1 deletion(-) diff --git a/include/linux/gfp.h b/include/linux/gfp.h index 4175dca4ac39..1a934383cc20 100644 --- a/include/linux/gfp.h +++ b/include/linux/gfp.h @@ -41,6 +41,11 @@ struct vm_area_struct; #define ___GFP_OTHER_NODE 0x800000u #define ___GFP_WRITE 0x1000000u #define ___GFP_KSWAPD_RECLAIM 0x2000000u +#ifdef CONFIG_LOCKDEP +#define ___GFP_NOLOCKDEP 0x4000000u +#else +#define ___GFP_NOLOCKDEP 0 +#endif /* If the above are modified, __GFP_BITS_SHIFT may need updating */ /* @@ -186,8 +191,11 @@ struct vm_area_struct; #define __GFP_NOTRACK_FALSE_POSITIVE (__GFP_NOTRACK) #define __GFP_OTHER_NODE ((__force gfp_t)___GFP_OTHER_NODE) +/* Disable lockdep for GFP context tracking */ +#define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP) + /* Room for N __GFP_FOO bits */ -#define __GFP_BITS_SHIFT 26 +#define __GFP_BITS_SHIFT (26 + IS_ENABLED(CONFIG_LOCKDEP)) #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1)) /* diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 7c38f8f3d97b..5684682a9ef8 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -2879,6 +2879,10 @@ static void __lockdep_trace_alloc(gfp_t gfp_mask, unsigned long flags) if (DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))) return; + /* Disable lockdep if explicitly requested */ + if (gfp_mask & __GFP_NOLOCKDEP) + return; + mark_held_locks(curr, RECLAIM_FS); } diff --git a/lib/radix-tree.c b/lib/radix-tree.c index 5e8fc32697b1..e528bd426f8e 100644 --- a/lib/radix-tree.c +++ b/lib/radix-tree.c @@ -2498,6 +2498,8 @@ static int radix_tree_cpu_dead(unsigned int cpu) void __init radix_tree_init(void) { int ret; + + BUILD_BUG_ON(RADIX_TREE_MAX_TAGS + __GFP_BITS_SHIFT > 32); radix_tree_node_cachep = kmem_cache_create("radix_tree_node", sizeof(struct radix_tree_node), 0, SLAB_PANIC | SLAB_RECLAIM_ACCOUNT, -- 2.10.2 -- 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
