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1 | /* |
2 | * Functions related to io context handling |
3 | */ |
4 | #include <linux/kernel.h> |
5 | #include <linux/module.h> |
6 | #include <linux/init.h> |
7 | #include <linux/bio.h> |
8 | #include <linux/blkdev.h> |
9 | #include <linux/bootmem.h> /* for max_pfn/max_low_pfn */ |
10 | |
11 | #include "blk.h" |
12 | |
13 | /* |
14 | * For io context allocations |
15 | */ |
16 | static struct kmem_cache *iocontext_cachep; |
17 | |
18 | static void cfq_dtor(struct io_context *ioc) |
19 | { |
20 | if (!hlist_empty(&ioc->cic_list)) { |
21 | struct cfq_io_context *cic; |
22 | |
23 | cic = list_entry(ioc->cic_list.first, struct cfq_io_context, |
24 | cic_list); |
25 | cic->dtor(ioc); |
26 | } |
27 | } |
28 | |
29 | /* |
30 | * IO Context helper functions. put_io_context() returns 1 if there are no |
31 | * more users of this io context, 0 otherwise. |
32 | */ |
33 | int put_io_context(struct io_context *ioc) |
34 | { |
35 | if (ioc == NULL) |
36 | return 1; |
37 | |
38 | BUG_ON(atomic_long_read(&ioc->refcount) == 0); |
39 | |
40 | if (atomic_long_dec_and_test(&ioc->refcount)) { |
41 | rcu_read_lock(); |
42 | if (ioc->aic && ioc->aic->dtor) |
43 | ioc->aic->dtor(ioc->aic); |
44 | cfq_dtor(ioc); |
45 | rcu_read_unlock(); |
46 | |
47 | kmem_cache_free(iocontext_cachep, ioc); |
48 | return 1; |
49 | } |
50 | return 0; |
51 | } |
52 | EXPORT_SYMBOL(put_io_context); |
53 | |
54 | static void cfq_exit(struct io_context *ioc) |
55 | { |
56 | rcu_read_lock(); |
57 | |
58 | if (!hlist_empty(&ioc->cic_list)) { |
59 | struct cfq_io_context *cic; |
60 | |
61 | cic = list_entry(ioc->cic_list.first, struct cfq_io_context, |
62 | cic_list); |
63 | cic->exit(ioc); |
64 | } |
65 | rcu_read_unlock(); |
66 | } |
67 | |
68 | /* Called by the exitting task */ |
69 | void exit_io_context(void) |
70 | { |
71 | struct io_context *ioc; |
72 | |
73 | task_lock(current); |
74 | ioc = current->io_context; |
75 | current->io_context = NULL; |
76 | task_unlock(current); |
77 | |
78 | if (atomic_dec_and_test(&ioc->nr_tasks)) { |
79 | if (ioc->aic && ioc->aic->exit) |
80 | ioc->aic->exit(ioc->aic); |
81 | cfq_exit(ioc); |
82 | |
83 | put_io_context(ioc); |
84 | } |
85 | } |
86 | |
87 | struct io_context *alloc_io_context(gfp_t gfp_flags, int node) |
88 | { |
89 | struct io_context *ret; |
90 | |
91 | ret = kmem_cache_alloc_node(iocontext_cachep, gfp_flags, node); |
92 | if (ret) { |
93 | atomic_long_set(&ret->refcount, 1); |
94 | atomic_set(&ret->nr_tasks, 1); |
95 | spin_lock_init(&ret->lock); |
96 | ret->ioprio_changed = 0; |
97 | ret->ioprio = 0; |
98 | ret->last_waited = jiffies; /* doesn't matter... */ |
99 | ret->nr_batch_requests = 0; /* because this is 0 */ |
100 | ret->aic = NULL; |
101 | INIT_RADIX_TREE(&ret->radix_root, GFP_ATOMIC | __GFP_HIGH); |
102 | INIT_HLIST_HEAD(&ret->cic_list); |
103 | ret->ioc_data = NULL; |
104 | } |
105 | |
106 | return ret; |
107 | } |
108 | |
109 | /* |
110 | * If the current task has no IO context then create one and initialise it. |
111 | * Otherwise, return its existing IO context. |
112 | * |
113 | * This returned IO context doesn't have a specifically elevated refcount, |
114 | * but since the current task itself holds a reference, the context can be |
115 | * used in general code, so long as it stays within `current` context. |
116 | */ |
117 | struct io_context *current_io_context(gfp_t gfp_flags, int node) |
118 | { |
119 | struct task_struct *tsk = current; |
120 | struct io_context *ret; |
121 | |
122 | ret = tsk->io_context; |
123 | if (likely(ret)) |
124 | return ret; |
125 | |
126 | ret = alloc_io_context(gfp_flags, node); |
127 | if (ret) { |
128 | /* make sure set_task_ioprio() sees the settings above */ |
129 | smp_wmb(); |
130 | tsk->io_context = ret; |
131 | } |
132 | |
133 | return ret; |
134 | } |
135 | |
136 | /* |
137 | * If the current task has no IO context then create one and initialise it. |
138 | * If it does have a context, take a ref on it. |
139 | * |
140 | * This is always called in the context of the task which submitted the I/O. |
141 | */ |
142 | struct io_context *get_io_context(gfp_t gfp_flags, int node) |
143 | { |
144 | struct io_context *ret = NULL; |
145 | |
146 | /* |
147 | * Check for unlikely race with exiting task. ioc ref count is |
148 | * zero when ioc is being detached. |
149 | */ |
150 | do { |
151 | ret = current_io_context(gfp_flags, node); |
152 | if (unlikely(!ret)) |
153 | break; |
154 | } while (!atomic_long_inc_not_zero(&ret->refcount)); |
155 | |
156 | return ret; |
157 | } |
158 | EXPORT_SYMBOL(get_io_context); |
159 | |
160 | void copy_io_context(struct io_context **pdst, struct io_context **psrc) |
161 | { |
162 | struct io_context *src = *psrc; |
163 | struct io_context *dst = *pdst; |
164 | |
165 | if (src) { |
166 | BUG_ON(atomic_long_read(&src->refcount) == 0); |
167 | atomic_long_inc(&src->refcount); |
168 | put_io_context(dst); |
169 | *pdst = src; |
170 | } |
171 | } |
172 | EXPORT_SYMBOL(copy_io_context); |
173 | |
174 | static int __init blk_ioc_init(void) |
175 | { |
176 | iocontext_cachep = kmem_cache_create("blkdev_ioc", |
177 | sizeof(struct io_context), 0, SLAB_PANIC, NULL); |
178 | return 0; |
179 | } |
180 | subsys_initcall(blk_ioc_init); |
181 |
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