Messages in this thread | | | From | Linus Torvalds <> | Date | Thu, 20 Dec 2001 11:46:23 -0800 | Subject | Re: ramdisk corruption problems - was: RE: pivot_root and initrd kern el panic woes |
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In article <D52B19A7284D32459CF20D579C4B0C0211CB0F@mail0.myrio.com> you write: >Yes, this does fix the problem. Thank you very much! > >Hopefully something like this will make it into 2.4.18?
This does not seem quite right.
>Tachino Nobuhiro (tachino@open.nm.fujitsu.co.jp) wrote: >> Hello, >> >> Following patch may fix your problem. >> >> diff -r -u linux-2.4.17-rc2.org/drivers/block/rd.c >> linux-2.4.17-rc2/drivers/block/rd.c >> --- linux-2.4.17-rc2.org/drivers/block/rd.c Thu Dec 20 20:30:57 2001 >> +++ linux-2.4.17-rc2/drivers/block/rd.c Thu Dec 20 20:46:53 2001 >> @@ -194,9 +194,11 @@ >> static int ramdisk_readpage(struct file *file, struct page * page) >> { >> if (!Page_Uptodate(page)) { >> - memset(kmap(page), 0, PAGE_CACHE_SIZE); >> - kunmap(page); >> - flush_dcache_page(page); >> + if (!page->buffers) { >> + memset(kmap(page), 0, PAGE_CACHE_SIZE); >> + kunmap(page); >> + flush_dcache_page(page); >> + } >> SetPageUptodate(page); >> } >> UnlockPage(page); >> >> >> grow_dev_page() creates not Uptodate page which has valid >> buffers, so >> it is wrong that ramdisk_readpage() clears whole page unconditionally.
The problem is that having buffers doesn't necessarily always mean that they are valid, nor that _all_ of them are valid.
Also, if the ramdisk "readpage" code is wrong, then so is the "prepare_write" code. They share the same logic, which basically says that "if the page isn't up-to-date, then it is zero". Which is always true for normal read/write accesses, but as you found out it's not true when parts of the page have been accessed by filesystems through the buffers.
So the code _should_ use a common helper, something like
static void ramdisk_updatepage(struct page * page) { if (!Page_Uptodate(page)) { struct buffer_head *bh = page->buffers; void * address = page_address(page); if (bh) { struct buffer_head *tmp = bh; do { if (!buffer_uptodate(tmp)) { memset(address, 0, tmp->b_size); set_buffer_uptodate(tmp); } address += tmp->b_size; tmp = tmp->b_this_page; } while (tmp != bh); } else memset(address, 0, PAGE_SIZE); flush_dcache_page(page); SetPageUptodate(page); } }
and then ramdisk_readpage() would just be
kmap(page); ramdisk_updatepage(page); UnlockPage(page); kunmap(page); return 0;
while ramdisk_prepare_write() would be
ramdisk_updatepage(page); SetPageDirty(page); return 0;
NOTE NOTE NOTE! This is untested. Please somebody test it, and in particular verify that there aren't any stupid highmem bugs, and resubmit the patch to me and Marcelo, ok?
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