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SubjectRe: [PATCH] Bug #3054 madvise(MADV_WILLNEED,...) fix for exceeding rlimit rss
Chris Wright wrote:

>* Matt Keenan (matthew.keenan@ntlworld.com) wrote:
>
>
>>--- linux-2.6.11.7/mm/madvise.c 2005-04-12 15:58:30.000000000 +0100
>>+++ linux/mm/madvise.c 2005-06-19 17:20:56.000000000 +0100
>>@@ -61,6 +61,7 @@ static long madvise_willneed(struct vm_a
>> unsigned long start, unsigned long end)
>>{
>> struct file *file = vma->vm_file;
>>+ struct task_struct *tsk = current;
>>
>>
>
>Looks like you've got some tab/whitespace damage going on here.
>
>
>
Damn mailer! I might have to go back to mutt.

>> if (!file)
>> return -EBADF;
>>@@ -70,6 +71,28 @@ static long madvise_willneed(struct vm_a
>> end = vma->vm_end;
>> end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
>>
>>+ /*
>>+ * This code below checks to see if mapping the requested
>>+ * readahead would make the task's rss exceed the task's
>>+ * rlimit rss.
>>+ *
>>+ * This doesn't account for pages that may already be mapped
>>+ * due to readahead, but since this is merely a hint to the
>>+ * kernel no harm should be done, it won't unmap anything
>>+ * already mapped if it fails. N.B. This won't affect the
>>+ * kernel's internal automatic readahead which doesn't check
>>+ * (or honour) rlimit rss.
>>+ */
>>+
>>+ spin_lock(&tsk->mm->page_table_lock);
>>+ if (((max_sane_readahead(end-start) << PAGE_SHIFT) +
>>+ tsk->mm->_rss) > tsk->signal->rlim[RLIMIT_RSS].rlim_cur)
>>
>>
>
>I doubt this one would overflow, but we recenly made changes in similar
>tests to use page count rather than byte count. I belive this should
>use get_mm_counter(). Isn't _rss counting pages rather than bytes,
>so I think the math is off here. Something like:
>
> if ((max_sane_readahead(end - start) + get_mm_counter(tsk->mm, rss)) >
> tsk->signal->rlim[RLIMIT_RSS].rlim_cur >> PAGE_SHIFT)
>
>
>
Ok, here is the patch again with the suggested fixes. I have attached
the patch (yes yes i know!), that will probably screw up people's mail
-> patch generators, but the whitespace issue should be fixed. Hopefully
this is ok, I'm going to bang on it for an hour or so here to make sure.

Signed-off-by: Matthew Keenan <matthew.keenan@ntlworld.com>


--- linux-2.6.11.7/mm/madvise.c 2005-04-12 15:58:30.000000000 +0100
+++ linux/mm/madvise.c 2005-06-19 21:39:57.000000000 +0100
@@ -61,6 +61,7 @@ static long madvise_willneed(struct vm_a
unsigned long start, unsigned long end)
{
struct file *file = vma->vm_file;
+ struct task_struct *tsk = current;

if (!file)
return -EBADF;
@@ -70,6 +71,28 @@ static long madvise_willneed(struct vm_a
end = vma->vm_end;
end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;

+ /*
+ * This code below checks to see if mapping the requested
+ * readahead would make the task's rss exceed the task's
+ * rlimit rss.
+ *
+ * This doesn't account for pages that may already be mapped
+ * due to readahead, but since this is merely a hint to the
+ * kernel no harm should be done, it won't unmap anything
+ * already mapped if it fails. N.B. This won't affect the
+ * kernel's internal automatic readahead which doesn't check
+ * (or honour) rlimit rss.
+ */
+
+ spin_lock(&tsk->mm->page_table_lock);
+ if ((max_sane_readahead(end - start) + get_mm_counter(tsk->mm, rss)) >
+ (tsk->signal->rlim[RLIMIT_RSS].rlim_cur >> PAGE_SHIFT))
+ {
+ spin_unlock(&tsk->mm->page_table_lock);
+ return -EIO;
+ }
+ spin_unlock(&tsk->mm->page_table_lock);
+
force_page_cache_readahead(file->f_mapping,
file, start, max_sane_readahead(end - start));
return 0;
@@ -170,6 +193,8 @@ static long madvise_vma(struct vm_area_s
* -ENOMEM - addresses in the specified range are not currently
* mapped, or are outside the AS of the process.
* -EIO - an I/O error occurred while paging in data.
+ * - MADV_WILLNEED would map in pages that would make the task's
+ * rss exceed rlimit rss.
* -EBADF - map exists, but area maps something that isn't a file.
* -EAGAIN - a kernel resource was temporarily unavailable.
*/
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