Messages in this thread | | | Subject | Re: [PATCH 1/2] topology: use bin_attribute to avoid buff overflow | From | "tiantao (H)" <> | Date | Wed, 2 Jun 2021 17:00:16 +0800 |
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在 2021/6/2 16:48, Andy Shevchenko 写道: > On Wed, Jun 2, 2021 at 9:45 AM tiantao (H) <tiantao6@huawei.com> wrote: >> 在 2021/6/2 14:18, Greg KH 写道: >>> On Wed, Jun 02, 2021 at 02:14:49PM +0800, tiantao (H) wrote: >>>> 在 2021/6/1 12:58, Greg KH 写道: >>>>> On Tue, Jun 01, 2021 at 10:56:49AM +0800, Tian Tao wrote: > ... > >>>>>> /** >>>>>> + * bitmap_print_to_buf - convert bitmap to list or hex format ASCII string >>>>>> + * @list: indicates whether the bitmap must be list >>>>>> + * @buf: page aligned buffer into which string is placed >>>>>> + * @maskp: pointer to bitmap to convert >>>>>> + * @nmaskbits: size of bitmap, in bits >>>>>> + * @off: offset in buf >>>>>> + * @count: count that already output >>>>>> + * >>>>>> + * the role of bitmap_print_to_buf and bitmap_print_to_pagebuf is >>>>>> + * the same, the difference is that the second parameter of >>>>>> + * bitmap_print_to_buf can be more than one pagesize. >>>>>> + */ >>>>>> +int bitmap_print_to_buf(bool list, char *buf, const unsigned long *maskp, >>>>>> + int nmaskbits, loff_t off, size_t count) >>>>>> +{ >>>>>> + int len, size; >>>>>> + void *data; >>>>>> + char *fmt = list ? "%*pbl\n" : "%*pb\n"; >>>>>> + >>>>>> + len = snprintf(NULL, 0, fmt, nmaskbits, maskp); >>>>>> + >>>>>> + data = kvmalloc(len+1, GFP_KERNEL); >>>>>> + if (!data) >>>>>> + return -ENOMEM; >>>>>> + >>>>>> + size = scnprintf(data, len+1, fmt, nmaskbits, maskp); >>>>>> + size = memory_read_from_buffer(buf, count, &off, data, size); >>>>>> + kvfree(data); >>>>>> + >>>>>> + return size; >>>>> Why is this so different from bitmap_print_to_pagebuf()? Can't you just >>>>> use this function as the "real" function and then change >>>>> bitmap_print_to_pagebuf() to call it with a size of PAGE_SIZE? >>>> Do you mean do following change, is that correct? :-) >>> Maybe, it is whitespace corrupted, and it still feels like this function >>> is much bigger than it needs to be given the function it is replacing is >>> only a simple sprintf() call. >>> >>>> +int bitmap_print_to_buf(bool list, char *buf, const unsigned long *maskp, >>>> + int nmaskbits, loff_t off, size_t count) >>>> +{ >>>> + int len, size; >>>> + void *data; >>>> + const char *fmt = list ? "%*pbl\n" : "%*pb\n"; >>>> + >>>> + if (off == LLONG_MAX && count == PAGE_SIZE - offset_in_page(buf)) >>>> + return scnprintf(buf, count, fmt, nmaskbits, maskp); >>>> + >>>> + len = snprintf(NULL, 0, fmt, nmaskbits, maskp); >>>> + >>>> + data = kvmalloc(len+1, GFP_KERNEL); >>> Why do you need to allocate more memory? And why kvmalloc()? >> Because the memory here will exceed a pagesize and we don't know the >> exact size, we have to call >> >> snprintf first to get the actual size. kvmalloc() is used because when >> physical memory is tight, kmalloc >> >> may fail, but vmalloc will succeed. It is not so bad that the memory is >> not requested here. > To me it sounds like the function is overengineered / lacks thought > through / optimization. > Can you provide a few examples that require the above algorithm?
so you think we should use kmalloc instead of kvmalloc ?
> >>>> + if (!data) >>>> + return -ENOMEM; >>>> + >>>> + size = scnprintf(data, len+1, fmt, nmaskbits, maskp); >>>> + >>>> + size = memory_read_from_buffer(buf, count, &off, data, size); >>>> + kvfree(data); >>>> + >>>> + return size; >>>> +} > > -- > With Best Regards, > Andy Shevchenko > . >
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