From 043f9b57247eafb8e28e7b9465470ece87090228 Mon Sep 17 00:00:00 2001 From: Brian Behlendorf Date: Mon, 26 Nov 2012 16:52:28 -0800 Subject: [PATCH] Disable FS reclaim when allocating new slabs Allowing the spl_cache_grow_work() function to reclaim inodes allows for two unlikely deadlocks. Therefore, we clear __GFP_FS for these allocations. The two deadlocks are: * While holding the ZFS_OBJ_HOLD_ENTER(zsb, obj1) lock a function calls kmem_cache_alloc() which happens to need to allocate a new slab. To allocate the new slab we enter FS level reclaim and attempt to evict several inodes. To evict these inodes we need to take the ZFS_OBJ_HOLD_ENTER(zsb, obj2) lock and it just happens that obj1 and obj2 use the same hashed lock. * Similar to the first case however instead of getting blocked on the hash lock we block in txg_wait_open() which is waiting for the next txg which isn't coming because the txg_sync thread is blocked in kmem_cache_alloc(). Note this isn't a 100% fix because vmalloc() won't strictly honor __GFP_FS. However, it practice this is sufficient because several very unlikely things must all occur concurrently. Signed-off-by: Brian Behlendorf Issue zfsonlinux/zfs#1101 --- module/spl/spl-kmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/module/spl/spl-kmem.c b/module/spl/spl-kmem.c index f3113e0f4..b171d446a 100644 --- a/module/spl/spl-kmem.c +++ b/module/spl/spl-kmem.c @@ -1773,7 +1773,7 @@ spl_cache_grow(spl_kmem_cache_t *skc, int flags, void **obj) atomic_inc(&skc->skc_ref); ska->ska_cache = skc; - ska->ska_flags = flags; + ska->ska_flags = flags & ~__GFP_FS; spl_init_delayed_work(&ska->ska_work, spl_cache_grow_work, ska); schedule_delayed_work(&ska->ska_work, 0); } -- 2.40.0