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authorBrian Behlendorf <[email protected]>2012-11-26 16:52:28 -0800
committerBrian Behlendorf <[email protected]>2012-11-27 13:43:27 -0800
commit043f9b57247eafb8e28e7b9465470ece87090228 (patch)
tree02c339bf4afa9748fffc14c9c86617c38ce0dc57 /module
parente71a4534b340228d2e73bdadacaff570ade5ab6a (diff)
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 <[email protected]> Issue zfsonlinux/zfs#1101
Diffstat (limited to 'module')
-rw-r--r--module/spl/spl-kmem.c2
1 files changed, 1 insertions, 1 deletions
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);
}