Re: [PATCH v1 2/3] fs/proc/page.c: allow inspection of last section and fix end detection

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On 10.12.19 02:04, kbuild test robot wrote:
> Hi David,
> 
> I love your patch! Yet something to improve:
> 
> [auto build test ERROR on linus/master]
> [also build test ERROR on linux/master v5.5-rc1 next-20191209]
> [cannot apply to mmotm/master]
> [if your patch is applied to the wrong git tree, please drop us a note to help
> improve the system. BTW, we also suggest to use '--base' option to specify the
> base tree in git format-patch, please see https://stackoverflow.com/a/37406982]
> 
> url:    https://github.com/0day-ci/linux/commits/David-Hildenbrand/mm-fix-max_pfn-not-falling-on-section-boundary/20191210-071011
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 6794862a16ef41f753abd75c03a152836e4c8028
> config: i386-defconfig (attached as .config)
> compiler: gcc-7 (Debian 7.5.0-1) 7.5.0
> reproduce:
>         # save the attached .config to linux build tree
>         make ARCH=i386 
> 
> If you fix the issue, kindly add following tag
> Reported-by: kbuild test robot <lkp@xxxxxxxxx>
> 
> All errors (new ones prefixed by >>):
> 
>    In file included from include/asm-generic/bug.h:19:0,
>                     from arch/x86/include/asm/bug.h:83,
>                     from include/linux/bug.h:5,
>                     from include/linux/mmdebug.h:5,
>                     from include/linux/mm.h:9,
>                     from include/linux/memblock.h:13,
>                     from fs/proc/page.c:2:
>    fs/proc/page.c: In function 'kpagecount_read':
>>> fs/proc/page.c:32:55: error: 'PAGES_PER_SECTION' undeclared (first use in this function); did you mean 'PAGE_KERNEL_IO'?
>      const unsigned long max_dump_pfn = round_up(max_pfn, PAGES_PER_SECTION);
>                                                           ^
>    include/linux/kernel.h:62:46: note: in definition of macro '__round_mask'
>     #define __round_mask(x, y) ((__typeof__(x))((y)-1))
>                                                  ^
>    fs/proc/page.c:32:37: note: in expansion of macro 'round_up'
>      const unsigned long max_dump_pfn = round_up(max_pfn, PAGES_PER_SECTION);
>                                         ^~~~~~~~
>    fs/proc/page.c:32:55: note: each undeclared identifier is reported only once for each function it appears in
>      const unsigned long max_dump_pfn = round_up(max_pfn, PAGES_PER_SECTION);
>                                                           ^
>    include/linux/kernel.h:62:46: note: in definition of macro '__round_mask'
>     #define __round_mask(x, y) ((__typeof__(x))((y)-1))
>                                                  ^
>    fs/proc/page.c:32:37: note: in expansion of macro 'round_up'
>      const unsigned long max_dump_pfn = round_up(max_pfn, PAGES_PER_SECTION);
>                                         ^~~~~~~~
>    fs/proc/page.c: In function 'kpageflags_read':
>    fs/proc/page.c:212:55: error: 'PAGES_PER_SECTION' undeclared (first use in this function); did you mean 'PAGE_KERNEL_IO'?
>      const unsigned long max_dump_pfn = round_up(max_pfn, PAGES_PER_SECTION);
>                                                           ^
>    include/linux/kernel.h:62:46: note: in definition of macro '__round_mask'
>     #define __round_mask(x, y) ((__typeof__(x))((y)-1))
>                                                  ^
>    fs/proc/page.c:212:37: note: in expansion of macro 'round_up'
>      const unsigned long max_dump_pfn = round_up(max_pfn, PAGES_PER_SECTION);
>                                         ^~~~~~~~
> 

So PAGES_PER_SECTION only applies to CONFIG_SPARSEMEM. Some local function
that messes with that should do the trick. Allows us to add a comment as
well :)

diff --git a/fs/proc/page.c b/fs/proc/page.c                                                                                                                                                                                                 
index e40dbfe1168e..2984df28ccea 100644                                                                                                                                                                                                      
--- a/fs/proc/page.c                                                                                                                                                                                    
+++ b/fs/proc/page.c                                                                                                                                                                                    
@@ -21,6 +21,21 @@                                                                                                                                                                              
 #define KPMMASK (KPMSIZE - 1)                                                                                                                                                                                                               
 #define KPMBITS (KPMSIZE * BITS_PER_BYTE)                                                                                                                                                                                                   
                                                                                                                            
+static inline unsigned long get_max_dump_pfn(void)                                                                                                                                                                                          
+{                                                                                                                              
+#ifdef CONFIG_SPARSEMEM                                                                                                                                                                                                
+       /*                                                                                                                                                      
+        * The memmap of early sections is completely populated and marked                                                                                                                                                                   
+        * online even if max_pfn does not fall on a section boundary -                                                                                                                                                                      
+        * pfn_to_online_page() will succeed on all pages. Allow inspecting                                                                                                                                                                  
+        * these memmaps.                                                                                                                                                                                                   
+        */                                                                                                                                                         
+       return round_up(max_pfn, PAGES_PER_SECTION);                                                                                                                                                                                         
+#else                                                                                                                                          
+       return max_pfn;                                                                                                                                                                                             
+#endif                                                                                                                                             
+}                                                                                                                              
+                                                                                                                           
 /* /proc/kpagecount - an array exposing page counts                                                                                                                                                                                         
  *                                                                                                                                 
  * Each entry is a u64 representing the corresponding                                                                                                                                                                                       
@@ -29,6 +44,7 @@                                                                                                                                                                           
 static ssize_t kpagecount_read(struct file *file, char __user *buf,                                                                                                                                                                         
                             size_t count, loff_t *ppos)                                                                                                                                                                                     
 {                                                                                                                              
+       const unsigned long max_dump_pfn = get_max_dump_pfn();
        u64 __user *out = (u64 __user *)buf;
        struct page *ppage;
        unsigned long src = *ppos;
@@ -37,9 +53,11 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf,
        u64 pcount;
 
        pfn = src / KPMSIZE;
-       count = min_t(size_t, count, (max_pfn * KPMSIZE) - src);
        if (src & KPMMASK || count & KPMMASK)
                return -EINVAL;
+       if (src >= max_dump_pfn * KPMSIZE)
+               return 0;
+       count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);
 
        while (count > 0) {
                /*
@@ -208,6 +226,7 @@ u64 stable_page_flags(struct page *page)
 static ssize_t kpageflags_read(struct file *file, char __user *buf,
                             size_t count, loff_t *ppos)
 {
+       const unsigned long max_dump_pfn = get_max_dump_pfn();
        u64 __user *out = (u64 __user *)buf;
        struct page *ppage;
        unsigned long src = *ppos;
@@ -215,9 +234,11 @@ static ssize_t kpageflags_read(struct file *file, char __user *buf,
        ssize_t ret = 0;
 
        pfn = src / KPMSIZE;
-       count = min_t(unsigned long, count, (max_pfn * KPMSIZE) - src);
        if (src & KPMMASK || count & KPMMASK)
                return -EINVAL;
+       if (src >= max_dump_pfn * KPMSIZE)
+               return 0;
+       count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);
 
        while (count > 0) {
                /*
@@ -253,6 +274,7 @@ static const struct file_operations proc_kpageflags_operations = {
 static ssize_t kpagecgroup_read(struct file *file, char __user *buf,
                                size_t count, loff_t *ppos)
 {
+       const unsigned long max_dump_pfn = get_max_dump_pfn();
        u64 __user *out = (u64 __user *)buf;
        struct page *ppage;
        unsigned long src = *ppos;
@@ -261,9 +283,11 @@ static ssize_t kpagecgroup_read(struct file *file, char __user *buf,
        u64 ino;
 
        pfn = src / KPMSIZE;
-       count = min_t(unsigned long, count, (max_pfn * KPMSIZE) - src);
        if (src & KPMMASK || count & KPMMASK)
                return -EINVAL;
+       if (src >= max_dump_pfn * KPMSIZE)
+               return 0;
+       count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);
 
        while (count > 0) {
                /*
-- 
2.21.0


-- 
Thanks,

David / dhildenb





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