On Wed, Jun 24, 2020 at 12:31 AM Dave Chinner david@fromorbit.com wrote:
On Sun, Jun 21, 2020 at 01:42:05PM -0400, Qian Cai wrote:
On Wed, Jun 10, 2020 at 09:41:01PM +0200, Daniel Vetter wrote:
fs_reclaim_acquire/release nicely catch recursion issues when allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend to use to keep the excessive caches in check). For mmu notifier recursions we do have lockdep annotations since 23b68395c7c7 ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end").
But these only fire if a path actually results in some pte invalidation - for most small allocations that's very rarely the case. The other trouble is that pte invalidation can happen any time when __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe choice, GFP_NOIO isn't good enough to avoid potential mmu notifier recursion.
I was pondering whether we should just do the general annotation, but there's always the risk for false positives. Plus I'm assuming that the core fs and io code is a lot better reviewed and tested than random mmu notifier code in drivers. Hence why I decide to only annotate for that specific case.
Furthermore even if we'd create a lockdep map for direct reclaim, we'd still need to explicit pull in the mmu notifier map - there's a lot more places that do pte invalidation than just direct reclaim, these two contexts arent the same.
Note that the mmu notifiers needing their own independent lockdep map is also the reason we can't hold them from fs_reclaim_acquire to fs_reclaim_release - it would nest with the acquistion in the pte invalidation code, causing a lockdep splat. And we can't remove the annotations from pte invalidation and all the other places since they're called from many other places than page reclaim. Hence we can only do the equivalent of might_lock, but on the raw lockdep map.
With this we can also remove the lockdep priming added in 66204f1d2d1b ("mm/mmu_notifiers: prime lockdep") since the new annotations are strictly more powerful.
v2: Review from Thomas Hellstrom:
- unbotch the fs_reclaim context check, I accidentally inverted it, but it didn't blow up because I inverted it immediately
- fix compiling for !CONFIG_MMU_NOTIFIER
Cc: Thomas Hellström (Intel) thomas_os@shipmail.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Jason Gunthorpe jgg@mellanox.com Cc: linux-mm@kvack.org Cc: linux-rdma@vger.kernel.org Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Christian König christian.koenig@amd.com Signed-off-by: Daniel Vetter daniel.vetter@intel.com
Replying the right patch here...
Reverting this commit [1] fixed the lockdep warning below while applying some memory pressure.
[1] linux-next cbf7c9d86d75 ("mm: track mmu notifiers in fs_reclaim_acquire/release")
[ 190.455003][ T369] WARNING: possible circular locking dependency detected [ 190.487291][ T369] 5.8.0-rc1-next-20200621 #1 Not tainted [ 190.512363][ T369] ------------------------------------------------------ [ 190.543354][ T369] kswapd3/369 is trying to acquire lock: [ 190.568523][ T369] ffff889fcf694528 (&xfs_nondir_ilock_class){++++}-{3:3}, at: xfs_reclaim_inode+0xdf/0x860 spin_lock at include/linux/spinlock.h:353 (inlined by) xfs_iflags_test_and_set at fs/xfs/xfs_inode.h:166 (inlined by) xfs_iflock_nowait at fs/xfs/xfs_inode.h:249 (inlined by) xfs_reclaim_inode at fs/xfs/xfs_icache.c:1127 [ 190.614359][ T369] [ 190.614359][ T369] but task is already holding lock: [ 190.647763][ T369] ffffffffb50ced00 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x0/0x30 __fs_reclaim_acquire at mm/page_alloc.c:4200 [ 190.687845][ T369] [ 190.687845][ T369] which lock already depends on the new lock. [ 190.687845][ T369] [ 190.734890][ T369] [ 190.734890][ T369] the existing dependency chain (in reverse order) is: [ 190.775991][ T369] [ 190.775991][ T369] -> #1 (fs_reclaim){+.+.}-{0:0}: [ 190.808150][ T369] fs_reclaim_acquire+0x77/0x80 [ 190.832152][ T369] slab_pre_alloc_hook.constprop.52+0x20/0x120 slab_pre_alloc_hook at mm/slab.h:507 [ 190.862173][ T369] kmem_cache_alloc+0x43/0x2a0 [ 190.885602][ T369] kmem_zone_alloc+0x113/0x3ef kmem_zone_alloc at fs/xfs/kmem.c:129 [ 190.908702][ T369] xfs_inode_item_init+0x1d/0xa0 xfs_inode_item_init at fs/xfs/xfs_inode_item.c:639 [ 190.934461][ T369] xfs_trans_ijoin+0x96/0x100 xfs_trans_ijoin at fs/xfs/libxfs/xfs_trans_inode.c:34 [ 190.961530][ T369] xfs_setattr_nonsize+0x1a6/0xcd0
OK, this patch has royally screwed something up if this path thinks it can enter memory reclaim. This path is inside a transaction, so it is running under PF_MEMALLOC_NOFS context, so should *never* enter memory reclaim.
I'd suggest that whatever mods were made to fs_reclaim_acquire by this patch broke it's basic functionality....
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 13cc653122b7..7536faaaa0fd 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -57,6 +57,7 @@ #include <trace/events/oom.h> #include <linux/prefetch.h> #include <linux/mm_inline.h> +#include <linux/mmu_notifier.h> #include <linux/migrate.h> #include <linux/hugetlb.h> #include <linux/sched/rt.h> @@ -4124,7 +4125,7 @@ should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_fla static struct lockdep_map __fs_reclaim_map = STATIC_LOCKDEP_MAP_INIT("fs_reclaim", &__fs_reclaim_map);
-static bool __need_fs_reclaim(gfp_t gfp_mask) +static bool __need_reclaim(gfp_t gfp_mask) { gfp_mask = current_gfp_context(gfp_mask);
This is applies the per-task memory allocation context flags to the mask that is checked here.
@@ -4136,10 +4137,6 @@ static bool __need_fs_reclaim(gfp_t gfp_mask) if (current->flags & PF_MEMALLOC) return false;
- /* We're only interested __GFP_FS allocations for now */
- if (!(gfp_mask & __GFP_FS))
return false;- if (gfp_mask & __GFP_NOLOCKDEP) return false;
@@ -4158,15 +4155,25 @@ void __fs_reclaim_release(void)
void fs_reclaim_acquire(gfp_t gfp_mask) {
- if (__need_fs_reclaim(gfp_mask))
__fs_reclaim_acquire();
- if (__need_reclaim(gfp_mask)) {
if (gfp_mask & __GFP_FS)__fs_reclaim_acquire();.... and they have not been applied in this path. There's your breakage.
For future reference, please post anything that changes NOFS allocation contexts or behaviours to linux-fsdevel, as filesystem developers need to know about proposed changes to infrastructure that is critical to the correct functioning of filesystems...
Uh crap I totally missed that. Apologies for wasting everyone's time here.
Andrew, please drop for now, I respin this thing. -Daniel