generic_file_write change in 2.4.0-ac8

Hi guys,

This code for generic_file_write calls vmtruncate without i_sem held. Is that intentional? It should cause problems for reiserfs at least...

-chris

diff -u --new-file --recursive --exclude-from /usr/src/exclude linux-2.4.0/mm/filemap.c linux.ac/mm/filemap.c

@@ -2578,6 +2625,13 @@
 	ClearPageUptodate(page);
 	kunmap(page);
 	goto unlock;
+sync_failure:
+	UnlockPage(page);
+	deactivate_page(page);
+	page_cache_release(page);
+	if (pos + bytes > inode->i_size)
+		vmtruncate(inode, inode->i_size);
+	goto done;
 }
 
 

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Erm... generic_file_write() grabs i_sem upon entry and drops it on exit. This call of vmtruncate() is deep inside the protected area.

It is taken out of the main path for obvious reasons, but as far as control flow counts it sits inside the main loop. FWIW, it might as well be written as

	....
	status = mapping->a_ops->prepare_write(.....);
	if (status) {
		UnlockPage(page);
		deactivate_page(page);
		page_cache_release(page);
		if (pos + bytes > inode->i_size)
			vmtruncate(inode, inode->i_size);
		break;
	}
	...

except that this variant would litter the main path. And the whole loop is under the ->i_sem - check the beginning of the function.

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Yup, I'm trying to track down a different problem, and saw what I wanted to instead of what was really there. Sigh.

-chris

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