fork.c bits for uClinux

PATCH In review Christoph Hellwig 1 participant 2 messages Nov 16, 2002 1 message not in the archive

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Christoph Hellwig

author

2002-11-16 22:10 UTC #0 lore raw

PATCH 1/1 fork.c bits for uClinux

mmuless ports don't need dup_mmap nor allocation of a pgd.

I tried to avoid ifdef-mess as far as possible, and to archive that I created small wrappers for pgd allocation/freeing and move taking of the mmap semaphore into dup_mmap from the only caller. The end result is just one additiona ifdef.

kernel/fork.c +23 -7

@@ -205,12 +205,14 @@
 	return tsk;
 }
 
+#ifdef CONFIG_MMU
 static inline int dup_mmap(struct mm_struct * mm)
 {
 	struct vm_area_struct * mpnt, *tmp, **pprev;
 	int retval;
 	unsigned long charge = 0;
 
+	down_write(&mm->mmap_sem);
 	flush_cache_mm(current->mm);
 	mm->locked_vm = 0;
 	mm->mmap = NULL;

@@ -287,11 +289,29 @@
 
 out:
 	flush_tlb_mm(current->mm);
+	up_write(&mm->mmap_sem);
 	return retval;
 fail_nomem:
 	vm_unacct_memory(charge);
 	goto out;
 }
+static inline int mm_alloc_pgd(struct mm_struct * mm)
+{
+	mm->pgd = pgd_alloc(mm);
+	if (unlikely(!mm->pgd))
+		return -ENOMEM;
+	return 0;
+}
+
+static inline void mm_free_pgd(struct mm_struct * mm)
+{
+	pgd_free(mm->pgd);
+}
+#else
+#define dup_mmap(mm)		(0)
+#define mm_alloc_pgd(mm)	(0)
+#define mm_free_pgd(mm)
+#endif /* CONFIG_MMU */
 
 spinlock_t mmlist_lock __cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;
 int mmlist_nr;

@@ -314,8 +334,7 @@
 	mm->default_kioctx = (struct kioctx)INIT_KIOCTX(mm->default_kioctx, *mm);
 	mm->free_area_cache = TASK_UNMAPPED_BASE;
 
-	mm->pgd = pgd_alloc(mm);
-	if (mm->pgd)
+	if (likely(!mm_alloc_pgd(mm)))
 		return mm;
 	free_mm(mm);
 	return NULL;

@@ -344,8 +363,8 @@
  */
 inline void __mmdrop(struct mm_struct *mm)
 {
-	if (mm == &init_mm) BUG();
-	pgd_free(mm->pgd);
+	BUG_ON(mm == &init_mm);
+	mm_free_pgd(mm);
 	destroy_context(mm);
 	free_mm(mm);
 }

@@ -444,10 +463,7 @@
 	if (init_new_context(tsk,mm))
 		goto free_pt;
 
-	down_write(&oldmm->mmap_sem);
 	retval = dup_mmap(mm);
-	up_write(&oldmm->mmap_sem);
-
 	if (retval)
 		goto free_pt;

A message that is not in the archive (sent off-list or not yet received): [email protected]

Christoph Hellwig

author

2002-11-16 22:37 UTC #2 lore raw

Quoted 7 lines · Ingo Oeser

The contents of the old struct mm_struct is copied and the semaphore of the old structure is taken. Now the content of the NEW semaphore is taken, which might be wrong, because the semaphore value is contained in the struct mm_struct and not a pointer.
Fix is to do give the oldmm as argument to dup_mm

Here's the update patch, thanks for the spot.

kernel/fork.c +26 -9

@@ -28,6 +28,7 @@
 #include <linux/security.h>
 #include <linux/futex.h>
 #include <linux/ptrace.h>
+#include <linux/mount.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>

@@ -205,12 +206,14 @@
 	return tsk;
 }
 
-static inline int dup_mmap(struct mm_struct * mm)
+#ifdef CONFIG_MMU
+static inline int dup_mmap(struct mm_struct * mm, struct mm_struct * oldmm)
 {
 	struct vm_area_struct * mpnt, *tmp, **pprev;
 	int retval;
 	unsigned long charge = 0;
 
+	down_write(&oldmm->mmap_sem);
 	flush_cache_mm(current->mm);
 	mm->locked_vm = 0;
 	mm->mmap = NULL;

@@ -287,11 +290,29 @@
 
 out:
 	flush_tlb_mm(current->mm);
+	up_write(&oldmm->mmap_sem);
 	return retval;
 fail_nomem:
 	vm_unacct_memory(charge);
 	goto out;
 }
+static inline int mm_alloc_pgd(struct mm_struct * mm)
+{
+	mm->pgd = pgd_alloc(mm);
+	if (unlikely(!mm->pgd))
+		return -ENOMEM;
+	return 0;
+}
+
+static inline void mm_free_pgd(struct mm_struct * mm)
+{
+	pgd_free(mm->pgd);
+}
+#else
+#define dup_mmap(mm, oldmm)	(0)
+#define mm_alloc_pgd(mm)	(0)
+#define mm_free_pgd(mm)
+#endif /* CONFIG_MMU */
 
 spinlock_t mmlist_lock __cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;
 int mmlist_nr;

@@ -314,8 +335,7 @@
 	mm->default_kioctx = (struct kioctx)INIT_KIOCTX(mm->default_kioctx, *mm);
 	mm->free_area_cache = TASK_UNMAPPED_BASE;
 
-	mm->pgd = pgd_alloc(mm);
-	if (mm->pgd)
+	if (likely(!mm_alloc_pgd(mm)))
 		return mm;
 	free_mm(mm);
 	return NULL;

@@ -344,8 +364,8 @@
  */
 inline void __mmdrop(struct mm_struct *mm)
 {
-	if (mm == &init_mm) BUG();
-	pgd_free(mm->pgd);
+	BUG_ON(mm == &init_mm);
+	mm_free_pgd(mm);
 	destroy_context(mm);
 	free_mm(mm);
 }

@@ -444,10 +464,7 @@
 	if (init_new_context(tsk,mm))
 		goto free_pt;
 
-	down_write(&oldmm->mmap_sem);
-	retval = dup_mmap(mm);
-	up_write(&oldmm->mmap_sem);
-
+	retval = dup_mmap(mm, oldmm);
 	if (retval)
 		goto free_pt;