Messages in this thread Patch in this message | | | From | Ulrich.Weigand@de ... | Date | Wed, 14 Mar 2001 18:49:33 +0100 | Subject | Bug in 2.2 update_vm_cache_conditional? |
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Hi Alan,
there appears to a bug in update_vm_cache_conditional that manifests itself only on S/390:
update_vm_cache_conditional is called with a source_address parameter that can either be a kernel or a user space virtual address, depending on how get_fs() is set.
update_vm_cache_conditional wants to check whether the source_address is in fact equal to the destination address in the page cache. This check should hit only when the source_address is actually a *kernel* space address; if the source is a user space address the page cache must always be updated.
However, update_vm_cache_conditional never checks whether the address is a kernel address, it does just a if ((unsigned long)dest != source_address)
On Intel, this is not a problem, as every user space address is different from every kernel space address anyway.
On S/390, however, the kernel lives in a separate address space, so shares the same range of addresses as the user spaces. This means that in certain rare cases, this check can accidentally hit even if the source lives in user space.
This leads to the page cache update being skipped, and the page cache is inconsistent with the buffer cache afterwards :-(
Do you agree that this is a bug? What do you think of this fix:
Index: filemap.c =================================================================== RCS file: /home/cvs/linux/mm/filemap.c,v retrieving revision 1.3 diff -u -r1.3 filemap.c --- filemap.c 2000/06/09 19:15:25 1.3 +++ filemap.c 2001/03/14 16:52:29 @@ -252,7 +252,8 @@ if (page) { char *dest = (char*) (offset + page_address(page));
- if ((unsigned long)dest != source_address) { + if ( (unsigned long)dest != source_address + || !segment_eq(get_fs(), KERNEL_DS)) { wait_on_page(page); memcpy(dest, buf, len); flush_dcache_page(page_address(page));
Mit freundlichen Gruessen / Best Regards
Ulrich Weigand
-- Dr. Ulrich Weigand Linux for S/390 Design & Development IBM Deutschland Entwicklung GmbH, Schoenaicher Str. 220, 71032 Boeblingen Phone: +49-7031/16-3727 --- Email: Ulrich.Weigand@de.ibm.com
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