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ida: make ida_simple_get/put() IRQ safe

PATCH In review Tejun Heo 2 participants 4 messages Oct 26, 2011 – Oct 28, 2011

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Tejun Heo

author
#0 lore raw

PATCH 1/1 ida: make ida_simple_get/put() IRQ safe

It's often convenient to be able to release resource from IRQ context. Make ida_simple_*() use irqsave/restore spin ops so that they are IRQ safe.

Signed-off-by Tejun Heo <[email protected]>
Acked-by Rusty Russell <[email protected]>

---
Andrew, can you please route this through mm?

Thank you.

 lib/idr.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)
lib/idr.c +7 -4
Index: work/lib/idr.c
===================================================================
@@ -944,6 +944,7 @@ int ida_simple_get(struct ida *ida, unsi
 {
 	int ret, id;
 	unsigned int max;
+	unsigned long flags;
 
 	BUG_ON((int)start < 0);
 	BUG_ON((int)end < 0);

@@ -959,7 +960,7 @@ again:
 	if (!ida_pre_get(ida, gfp_mask))
 		return -ENOMEM;
 
-	spin_lock(&simple_ida_lock);
+	spin_lock_irqsave(&simple_ida_lock, flags);
 	ret = ida_get_new_above(ida, start, &id);
 	if (!ret) {
 		if (id > max) {

@@ -969,7 +970,7 @@ again:
 			ret = id;
 		}
 	}
-	spin_unlock(&simple_ida_lock);
+	spin_unlock_irqrestore(&simple_ida_lock, flags);
 
 	if (unlikely(ret == -EAGAIN))
 		goto again;

@@ -985,10 +986,12 @@ EXPORT_SYMBOL(ida_simple_get);
  */
 void ida_simple_remove(struct ida *ida, unsigned int id)
 {
+	unsigned long flags;
+
 	BUG_ON((int)id < 0);
-	spin_lock(&simple_ida_lock);
+	spin_lock_irqsave(&simple_ida_lock, flags);
 	ida_remove(ida, id);
-	spin_unlock(&simple_ida_lock);
+	spin_unlock_irqrestore(&simple_ida_lock, flags);
 }
 EXPORT_SYMBOL(ida_simple_remove);
maintainer
#1 lore raw
Quoted 3 lines · On Wed, 26 Oct 2011 13:33:11 -0700 Tejun Heo <[email protected]> wrote:

It's often convenient to be able to release resource from IRQ context. Make ida_simple_*() use irqsave/restore spin ops so that they are IRQ safe.

The patch also accidentally makes ida_simple_get() callable from interrupt context. That's a somewhat unreliable operation due to -ENOMEM possibilities even with GFP_ATOMIC.

Quoted 32 lines
lib/idr.c +3 -2
@@ -944,6 +944,7 @@ int ida_simple_get(struct ida *ida, unsi
 {
 	int ret, id;
 	unsigned int max;
+	unsigned long flags;
 
 	BUG_ON((int)start < 0);
 	BUG_ON((int)end < 0);

@@ -959,7 +960,7 @@ again:
 	if (!ida_pre_get(ida, gfp_mask))
 		return -ENOMEM;
 
-	spin_lock(&simple_ida_lock);
+	spin_lock_irqsave(&simple_ida_lock, flags);
 	ret = ida_get_new_above(ida, start, &id);
 	if (!ret) {
 		if (id > max) {

@@ -969,7 +970,7 @@ again:
 			ret = id;
 		}
 	}
-	spin_unlock(&simple_ida_lock);
+	spin_unlock_irqrestore(&simple_ida_lock, flags);
 
 	if (unlikely(ret == -EAGAIN))
 		goto again;

@@ -985,10 +986,12 @@ EXPORT_SYMBOL(ida_simple_get);
  */
 void ida_simple_remove(struct ida *ida, unsigned int id)
 {

lib/idr.c EXPORT_SYMBOL(ida_simple_get); · line 996

Quoted 10 lines
lib/idr.c +4 -2
+	unsigned long flags;
+
 	BUG_ON((int)id < 0);
-	spin_lock(&simple_ida_lock);
+	spin_lock_irqsave(&simple_ida_lock, flags);
 	ida_remove(ida, id);
-	spin_unlock(&simple_ida_lock);
+	spin_unlock_irqrestore(&simple_ida_lock, flags);
 }
 EXPORT_SYMBOL(ida_simple_remove);

It didn't update the kerneldoc. I wouldn't have bothered either ;) We're generally bad about documenting permissible calling environments and preconditions.

author
#2 lore raw
Quoted 10 lines · Andrew Morton
Quoted 3 lines · On Wed, 26 Oct 2011 13:33:11 -0700 Tejun Heo <[email protected]> wrote:

It's often convenient to be able to release resource from IRQ context. Make ida_simple_*() use irqsave/restore spin ops so that they are IRQ safe.

The patch also accidentally makes ida_simple_get() callable from interrupt context. That's a somewhat unreliable operation due to -ENOMEM possibilities even with GFP_ATOMIC.

Hmmm... We can add a WARN_ON_ONCE() there but do we really care? If the caller is using GFP_ATOMIC, it should be expecting unreliability.

Thanks.

Signature · 1 line
tejun
maintainer
#3 lore raw
Quoted 8 lines · On Fri, 28 Oct 2011 16:11:49 -0700 Tejun Heo <[email protected]> wrote:
Quoted 7 lines · Andrew Morton
Quoted 3 lines · On Wed, 26 Oct 2011 13:33:11 -0700 Tejun Heo <[email protected]> wrote:

It's often convenient to be able to release resource from IRQ context. Make ida_simple_*() use irqsave/restore spin ops so that they are IRQ safe.

Quoted 7 lines
Quoted 3 lines

The patch also accidentally makes ida_simple_get() callable from interrupt context. That's a somewhat unreliable operation due to -ENOMEM possibilities even with GFP_ATOMIC.

Hmmm... We can add a WARN_ON_ONCE() there but do we really care? If the caller is using GFP_ATOMIC, it should be expecting unreliability.

No, I don't think we care - I was just chin-scratching and augmenting some deficient changeloggery. Also, showing that I'd actually read the thing ;)