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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 <behlendorf1@llnl.gov> Issue zfsonlinux/zfs#1101
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@ -1773,7 +1773,7 @@ spl_cache_grow(spl_kmem_cache_t *skc, int flags, void **obj)
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atomic_inc(&skc->skc_ref);
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ska->ska_cache = skc;
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ska->ska_flags = flags;
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ska->ska_flags = flags & ~__GFP_FS;
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spl_init_delayed_work(&ska->ska_work, spl_cache_grow_work, ska);
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schedule_delayed_work(&ska->ska_work, 0);
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}
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