[PATCH 1/1] utrace: introduce UTRACE_ATTACH_ATOMIC

[Oleg Nesterov]

Add the new UTRACE_ATTACH_ATOMIC flag for utrace_attach_task().
If it is set, UTRACE_ATTACH_CREATE uses GFP_ATOMIC for memory
allocations and thus it can be used in atomic context.

Suggested-by: Mark Wielaard <mjw at redhat.com>
Signed-off-by: Oleg Nesterov <oleg at redhat.com>
---
 include/linux/utrace.h |    1 +
 kernel/utrace.c        |   12 ++++++++----
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/include/linux/utrace.h b/include/linux/utrace.h
index f37373b..46959af 100644
--- a/include/linux/utrace.h
+++ b/include/linux/utrace.h
@@ -317,6 +317,7 @@ static inline enum utrace_syscall_action utrace_syscall_action(u32 action)
 #define UTRACE_ATTACH_MATCH_MASK	0x000f
 #define UTRACE_ATTACH_CREATE		0x0010 /* Attach a new engine.  */
 #define UTRACE_ATTACH_EXCLUSIVE		0x0020 /* Refuse if existing match.  */
+#define UTRACE_ATTACH_ATOMIC		0x0040 /* For _CREATE, don't sleep  */
 
 /**
  * struct utrace_engine - per-engine structure
diff --git a/kernel/utrace.c b/kernel/utrace.c
index c817a46..a169e1b 100644
--- a/kernel/utrace.c
+++ b/kernel/utrace.c
@@ -113,9 +113,9 @@ void task_utrace_unlock(struct task_struct *task)
  *
  * This returns false only in case of a memory allocation failure.
  */
-static bool utrace_task_alloc(struct task_struct *task)
+static bool utrace_task_alloc(struct task_struct *task, gfp_t gfp_flags)
 {
-	struct utrace *utrace = kmem_cache_zalloc(utrace_cachep, GFP_KERNEL);
+	struct utrace *utrace = kmem_cache_zalloc(utrace_cachep, gfp_flags);
 	if (unlikely(!utrace))
 		return false;
 	spin_lock_init(&utrace->lock);
@@ -295,6 +295,7 @@ struct utrace_engine *utrace_attach_task(
 {
 	struct utrace *utrace = task_utrace_struct(target);
 	struct utrace_engine *engine;
+	gfp_t gfp_flags;
 	int ret;
 
 	if (!(flags & UTRACE_ATTACH_CREATE)) {
@@ -317,13 +318,16 @@ struct utrace_engine *utrace_attach_task(
 		 */
 		return ERR_PTR(-EPERM);
 
+	gfp_flags = (flags & UTRACE_ATTACH_ATOMIC)
+				? GFP_ATOMIC : GFP_KERNEL;
+
 	if (!utrace) {
-		if (unlikely(!utrace_task_alloc(target)))
+		if (unlikely(!utrace_task_alloc(target, gfp_flags)))
 			return ERR_PTR(-ENOMEM);
 		utrace = task_utrace_struct(target);
 	}
 
-	engine = kmem_cache_alloc(utrace_engine_cachep, GFP_KERNEL);
+	engine = kmem_cache_alloc(utrace_engine_cachep, gfp_flags);
 	if (unlikely(!engine))
 		return ERR_PTR(-ENOMEM);
 
-- 
1.5.5.1