Hi,
We have two Freescale PowerPC boards on which we're trying to enable
DEBUG_PAGEALLOC with the hope that we'll see an exception whenever some
code tries to modify a page that's been already freed. To test it, we wrote
this sample code -
===
#define BUF_SIZE 4096
void
pagealloc_test(void)
{
char *buf = kmalloc(BUF_SIZE, GFP_KERNEL);
if (!buf) {
printk("%s[%d] - alloc failed!\n", __func__, __LINE__);
return;
}
printk("%s[%d] - alloc'd\n", __func__, __LINE__);
memset(&buf[0], 0, BUF_SIZE);
printk("%s[%d] - memset'd\n", __func__, __LINE__);
kfree(buf);
printk("%s[%d] - free'd\n", __func__, __LINE__);
memset(&buf[0], 1, BUF_SIZE);
printk("%s[%d] - memset'd after free!\n", __func__, __LINE__);
}
===
Here, the last memset() should generate an exception if PAGEALLOC code
correctly unmapped the page during kfree(). However, kernel is happily
running after the memset post-free. Any clue?
Also, the 2nd board has Book-E which has a different MMU architecture.
Here, I saw that the function __change_page_attr() always returns as the
condition v_mapped_by_tlbcam() is true. How do we remove the pte entry from
the TLB in this case? Has anyone tried DEBUG_PAGEALLOC on Book-E?
Please find the board details below -
Board 1: CPU - e300c4, kernel 2.6-25
==============================
======
CONFIG_6xx=y
CONFIG_PPC_FPU=y
CONFIG_PPC_STD_MMU=y
CONFIG_PPC_STD_MMU_32=y
CONFIG_PPC32=y
CONFIG_WORD_SIZE=32
CONFIG_PPC_MERGE=y
CONFIG_MMU=y
CONFIG_IRQ_PER_CPU=y
CONFIG_PPC=y
Board 2: CPU - e500v2, kernel 3.0-34
====================================
# CONFIG_PPC_BOOK3S_32 is not set
CONFIG_PPC_85xx=y
CONFIG_E500=y
# CONFIG_PPC_E500MC is not set
CONFIG_FSL_EMB_PERFMON=y
CONFIG_BOOKE=y
CONFIG_FSL_BOOKE=y
CONFIG_PPC_FSL_BOOK3E=y
# CONFIG_PHYS_64BIT is not set
CONFIG_SPE=y
CONFIG_PPC_MMU_NOHASH=y
CONFIG_PPC_MMU_NOHASH_32=y
CONFIG_PPC_BOOK3E_MMU=y
# CONFIG_PPC_MM_SLICES is not set
CONFIG_SMP=y
CONFIG_NR_CPUS=2
CONFIG_PPC32=y
CONFIG_32BIT=y
CONFIG_WORD_SIZE=32
# CONFIG_ARCH_PHYS_ADDR_T_64BIT is not set
# CONFIG_ARCH_DMA_ADDR_T_64BIT is not set
CONFIG_MMU=y
CONFIG_NR_IRQS=512
CONFIG_PPC=y
Regards,
Partha
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