I actually forgot to cc linux-fsdevel on this one.
Vladimir found a corner case bug in the case of faulting source
address, which is since fixed, but might be interesting to anyone
else following development...
- Forwarded message from Nick Piggin [EMAIL PROTECTED] -
Date: Wed, 16 May 2007 09:14:06 +0200
From: Nick Piggin [EMAIL PROTECTED]
To: Vladimir V. Saveliev [EMAIL PROTECTED]
Cc: Andrew Morton [EMAIL PROTECTED]
Subject: Re: [patch 00/41] Buffered write deadlock fix and new aops for
2.6.21-mm2
In-Reply-To: [EMAIL PROTECTED]
User-Agent: Mutt/1.5.9i
cc'ed linux-fsdevel again...
On Tue, May 15, 2007 at 10:00:38PM +0400, Vladimir V. Saveliev wrote:
Hello
On Tuesday 15 May 2007 02:42, Nick Piggin wrote:
On Mon, May 14, 2007 at 10:28:45PM +0400, Vladimir V. Saveliev wrote:
Hello
There is a problem with new write.
If you expand an empty file with truncate and then write so that in one
write file tail is overwritten and something is appended to the file -
the write loops forever
writing to page containing file tail. Something wrong happens writing to
uptodate last page of a file, I guess.
I can send a simple program if necessary.
Is this reiserfs with your reiserfs patch?
No, this is common problem. I get it easily on ext3 and ext2.
Yes, please send a simple
program and I'll have a look.
Thanks, that was really helpful!
What the program does is to write a non-faulted page into pagecache,
which means we're relying on fault_in_pages_readable to bring it in
for us. Usually it does, however your specific write pattern required
that 2 pages be brought in, and _also_ that the total number of bytes
to write went past that 2nd page.
This caused the 1st and an Nth (2) page to be faulted in, but the
atomic copy_from_user really needed the 2nd page :)
This fixes it for me.
---
Index: linux-2.6/include/linux/fs.h
===
--- linux-2.6.orig/include/linux/fs.h 2007-05-16 16:58:41.0 +1000
+++ linux-2.6/include/linux/fs.h2007-05-16 16:58:47.0 +1000
@@ -419,7 +419,7 @@
size_t iov_iter_copy_from_user(struct page *page,
struct iov_iter *i, unsigned long offset, size_t bytes);
void iov_iter_advance(struct iov_iter *i, size_t bytes);
-int iov_iter_fault_in_readable(struct iov_iter *i);
+int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes);
size_t iov_iter_single_seg_count(struct iov_iter *i);
static inline void iov_iter_init(struct iov_iter *i,
Index: linux-2.6/mm/filemap.c
===
--- linux-2.6.orig/mm/filemap.c 2007-05-16 14:11:18.0 +1000
+++ linux-2.6/mm/filemap.c 2007-05-16 17:03:29.0 +1000
@@ -1806,11 +1806,10 @@
}
EXPORT_SYMBOL(iov_iter_advance);
-int iov_iter_fault_in_readable(struct iov_iter *i)
+int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
{
- size_t seglen = min(i-iov-iov_len - i-iov_offset, i-count);
char __user *buf = i-iov-iov_base + i-iov_offset;
- return fault_in_pages_readable(buf, seglen);
+ return fault_in_pages_readable(buf, bytes);
}
EXPORT_SYMBOL(iov_iter_fault_in_readable);
@@ -2102,7 +2101,7 @@
* to check that the address is actually valid, when atomic
* usercopies are used, below.
*/
- if (unlikely(iov_iter_fault_in_readable(i))) {
+ if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
status = -EFAULT;
break;
}
@@ -2276,7 +2275,7 @@
* to check that the address is actually valid, when atomic
* usercopies are used, below.
*/
- if (unlikely(iov_iter_fault_in_readable(i))) {
+ if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
status = -EFAULT;
break;
}
- End forwarded message -
-
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