(Apologies in advance if you already know about this)
I've just been chasing down the problem with writes to mmap()d areas hanging,
and it turns out that filemap_nopage() will try to clobber page 0 if the
page isn't found in the page cache and no_share is true:
no_cached_page:
.
.
.
/*
* Now it's ours and locked, we can do initial IO to it:
*/
new_page = 0;
page_not_uptodate:
error = inode->i_op->readpage(file, page);
if (!error) {
wait_on_page(page);
if (PageError(page))
goto page_read_error;
goto success;
}
success:
old_page = page_address(page);
if (!no_share) {
...
}
/*
* No sharing ... copy to the new page.
*/
if (!new_page)
printk(KERN_CRIT "filemap_nopage(): erk, new_page == 0\n");
copy_page(new_page, old_page);
I don't claim to understand (yet) what the fix is; I'm also not on clear why
the page fault handler just tries to re-enter itself, ultimately deadlocking
on current->mm->mmap_sem -- does it show that I'm /way/ out of my depth
here? ;-)
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