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authorSteven Rostedt <rostedt@goodmis.org>2009-01-29 10:08:01 -0500
committerIngo Molnar <mingo@elte.hu>2009-01-30 12:31:08 -0500
commitd7240b988017521ebf89edfadd42c0942f166850 (patch)
tree07bdbb42405e0d247f719d45464760d0dd12864c /kernel
parent4ab0a9409af5fad74ad1fc9e46d5a8b460f353e9 (diff)
generic-ipi: use per cpu data for single cpu ipi calls
The smp_call_function can be passed a wait parameter telling it to wait for all the functions running on other CPUs to complete before returning, or to return without waiting. Unfortunately, this is currently just a suggestion and not manditory. That is, the smp_call_function can decide not to return and wait instead. The reason for this is because it uses kmalloc to allocate storage to send to the called CPU and that CPU will free it when it is done. But if we fail to allocate the storage, the stack is used instead. This means we must wait for the called CPU to finish before continuing. Unfortunatly, some callers do no abide by this hint and act as if the non-wait option is mandatory. The MTRR code for instance will deadlock if the smp_call_function is set to wait. This is because the smp_call_function will wait for the other CPUs to finish their called functions, but those functions are waiting on the caller to continue. This patch changes the generic smp_call_function code to use per cpu variables if the allocation of the data fails for a single CPU call. The smp_call_function_many will fall back to the smp_call_function_single if it fails its alloc. The smp_call_function_single is modified to not force the wait state. Since we now are using a single data per cpu we must synchronize the callers to prevent a second caller modifying the data before the first called IPI functions complete. To do so, I added a flag to the call_single_data called CSD_FLAG_LOCK. When the single CPU is called (which can be called when a many call fails an alloc), we set the LOCK bit on this per cpu data. When the caller finishes it clears the LOCK bit. The caller must wait till the LOCK bit is cleared before setting it. When it is cleared, there is no IPI function using it. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Jens Axboe <jens.axboe@oracle.com> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/smp.c36
1 files changed, 33 insertions, 3 deletions
diff --git a/kernel/smp.c b/kernel/smp.c
index 5cfa0e5e3e88..bbedbb7efe32 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -18,6 +18,7 @@ __cacheline_aligned_in_smp DEFINE_SPINLOCK(call_function_lock);
18enum { 18enum {
19 CSD_FLAG_WAIT = 0x01, 19 CSD_FLAG_WAIT = 0x01,
20 CSD_FLAG_ALLOC = 0x02, 20 CSD_FLAG_ALLOC = 0x02,
21 CSD_FLAG_LOCK = 0x04,
21}; 22};
22 23
23struct call_function_data { 24struct call_function_data {
@@ -186,6 +187,9 @@ void generic_smp_call_function_single_interrupt(void)
186 if (data_flags & CSD_FLAG_WAIT) { 187 if (data_flags & CSD_FLAG_WAIT) {
187 smp_wmb(); 188 smp_wmb();
188 data->flags &= ~CSD_FLAG_WAIT; 189 data->flags &= ~CSD_FLAG_WAIT;
190 } else if (data_flags & CSD_FLAG_LOCK) {
191 smp_wmb();
192 data->flags &= ~CSD_FLAG_LOCK;
189 } else if (data_flags & CSD_FLAG_ALLOC) 193 } else if (data_flags & CSD_FLAG_ALLOC)
190 kfree(data); 194 kfree(data);
191 } 195 }
@@ -196,6 +200,8 @@ void generic_smp_call_function_single_interrupt(void)
196 } 200 }
197} 201}
198 202
203static DEFINE_PER_CPU(struct call_single_data, csd_data);
204
199/* 205/*
200 * smp_call_function_single - Run a function on a specific CPU 206 * smp_call_function_single - Run a function on a specific CPU
201 * @func: The function to run. This must be fast and non-blocking. 207 * @func: The function to run. This must be fast and non-blocking.
@@ -224,14 +230,38 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
224 func(info); 230 func(info);
225 local_irq_restore(flags); 231 local_irq_restore(flags);
226 } else if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) { 232 } else if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
227 struct call_single_data *data = NULL; 233 struct call_single_data *data;
228 234
229 if (!wait) { 235 if (!wait) {
236 /*
237 * We are calling a function on a single CPU
238 * and we are not going to wait for it to finish.
239 * We first try to allocate the data, but if we
240 * fail, we fall back to use a per cpu data to pass
241 * the information to that CPU. Since all callers
242 * of this code will use the same data, we must
243 * synchronize the callers to prevent a new caller
244 * from corrupting the data before the callee
245 * can access it.
246 *
247 * The CSD_FLAG_LOCK is used to let us know when
248 * the IPI handler is done with the data.
249 * The first caller will set it, and the callee
250 * will clear it. The next caller must wait for
251 * it to clear before we set it again. This
252 * will make sure the callee is done with the
253 * data before a new caller will use it.
254 */
230 data = kmalloc(sizeof(*data), GFP_ATOMIC); 255 data = kmalloc(sizeof(*data), GFP_ATOMIC);
231 if (data) 256 if (data)
232 data->flags = CSD_FLAG_ALLOC; 257 data->flags = CSD_FLAG_ALLOC;
233 } 258 else {
234 if (!data) { 259 data = &per_cpu(csd_data, me);
260 while (data->flags & CSD_FLAG_LOCK)
261 cpu_relax();
262 data->flags = CSD_FLAG_LOCK;
263 }
264 } else {
235 data = &d; 265 data = &d;
236 data->flags = CSD_FLAG_WAIT; 266 data->flags = CSD_FLAG_WAIT;
237 } 267 }