Re: [V2 PATCH 1/1] mm: msync: fix issues of sys_msync on tmpfs

[Bruce Ashfield <bruce.ashfield@windriver.com>]

On 12-01-03 11:53 PM, Khem Raj wrote:
> On (22/12/11 09:24), Bruce Ashfield wrote:
>> On 11-12-21 10:07 PM, Zumeng Chen wrote:
>>> There are two problems as follows shown:
>>> 1 ) for TMPFS, nothing need to be done in sys_msync,
>>>      sys_msync just return 0 for all arches.
>>>
>>> 2 ) But for MIPS CPUs with cache alias(dmesg|grep alias),
>>>      it maybe has the issue, which reported by msync test
>>>      suites in ltp-full, when the memory of memset used by
>>>      msycn01 has cache alias.
>>>      So, in this situation, we have to flush the related
>>>      vma to make sure correct read.
>>
>> Looks good. I'll queue this for the next kernel update.
>>
>
>
> has this been proposed to lkml ?

Not yet. We are still reviewing it @ Wind River via our process, and
since we picked it up on MIPS, we are running it past Ralf as well.
Still time to get it in place for 3.3, if it is legit.

Cheers,

Bruce

>
>> Cheers,
>>
>> Bruce
>>
>>>
>>> Signed-off-by: Zumeng Chen<zumeng.chen@windriver.com>
>>> ---
>>>   include/linux/shmem_fs.h |   10 ++++++++++
>>>   mm/msync.c               |   22 +++++++++++++++++++++-
>>>   mm/shmem.c               |    5 +++++
>>>   3 files changed, 36 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
>>> index aa08fa8..62a2d57 100644
>>> --- a/include/linux/shmem_fs.h
>>> +++ b/include/linux/shmem_fs.h
>>> @@ -12,6 +12,15 @@
>>>
>>>   #define SHMEM_SYMLINK_INLINE_LEN (SHMEM_NR_DIRECT * sizeof(swp_entry_t))
>>>
>>> +/*
>>> +
>>> +*/
>>> +#ifndef cpu_has_dc_aliases
>>> +#define CPU_HAS_CACHE_ALIAS 0
>>> +#else
>>> +#define CPU_HAS_CACHE_ALIAS cpu_has_dc_aliases
>>> +#endif
>>> +
>>>   struct shmem_inode_info {
>>>   	spinlock_t		lock;
>>>   	unsigned long		flags;
>>> @@ -49,6 +58,7 @@ static inline struct shmem_inode_info *SHMEM_I(struct inode *inode)
>>>   /*
>>>    * Functions in mm/shmem.c called directly from elsewhere:
>>>    */
>>> +extern int is_shmem_file(struct file *file);
>>>   extern int init_tmpfs(void);
>>>   extern int shmem_fill_super(struct super_block *sb, void *data, int silent);
>>>   extern struct file *shmem_file_setup(const char *name,
>>> diff --git a/mm/msync.c b/mm/msync.c
>>> index 632df45..84cb068 100644
>>> --- a/mm/msync.c
>>> +++ b/mm/msync.c
>>> @@ -13,6 +13,8 @@
>>>   #include<linux/file.h>
>>>   #include<linux/syscalls.h>
>>>   #include<linux/sched.h>
>>> +#include<linux/shmem_fs.h>
>>> +#include<asm/cacheflush.h>
>>>
>>>   /*
>>>    * MS_SYNC syncs the entire file - including mappings.
>>> @@ -33,6 +35,7 @@ SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)
>>>   	unsigned long end;
>>>   	struct mm_struct *mm = current->mm;
>>>   	struct vm_area_struct *vma;
>>> +	struct file *file;
>>>   	int unmapped_error = 0;
>>>   	int error = -EINVAL;
>>>
>>> @@ -56,8 +59,25 @@ SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)
>>>   	 */
>>>   	down_read(&mm->mmap_sem);
>>>   	vma = find_vma(mm, start);
>>> +
>>> +#ifdef CONFIG_TMPFS
>>> +	/*
>>> +	 * For tmpfs, no matter which flag(ASYNC or SYNC) gets from msync,
>>> +	 * there is not so much thing to do for CPUs without cache alias,
>>> +	 * But for some CPUs with cache alias, msync has to flush cache
>>> +	 * explicitly, which makes sure the data coherency between memory
>>> +	 * file and cache.
>>> +	 */
>>> +	file =  vma->vm_file;
>>> +	if (is_shmem_file(file)) {
>>> +		if(CPU_HAS_CACHE_ALIAS)
>>> +			flush_cache_range(vma, start, start+len);
>>> +		error = 0;
>>> +		goto out_unlock;
>>> +	}
>>> +#endif
>>> +
>>>   	for (;;) {
>>> -		struct file *file;
>>>
>>>   		/* Still start<   end. */
>>>   		error = -ENOMEM;
>>> diff --git a/mm/shmem.c b/mm/shmem.c
>>> index 92e5c15..4fabfac 100644
>>> --- a/mm/shmem.c
>>> +++ b/mm/shmem.c
>>> @@ -2793,6 +2793,11 @@ static struct file_system_type tmpfs_fs_type = {
>>>   	.kill_sb	= kill_litter_super,
>>>   };
>>>
>>> +int is_shmem_file(struct file *file)
>>> +{
>>> +	return (file->f_op ==&shmem_file_operations)? 1 : 0;
>>> +}
>>> +
>>>   int __init init_tmpfs(void)
>>>   {
>>>   	int error;
>>
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