Hi,
>
> static void bad_page(struct page *page)
> {
> printk(KERN_EMERG "Bad page state in process '%s'\n"
> KERN_EMERG "page:%p flags:0x%0*lx mapping:%p
> mapcount:%d count:%d\n"
> KERN_EMERG "Trying to fix it up, but a reboot is
> needed\n" KERN_EMERG "Backtrace:\n",
> current->comm, page, (int)(2*sizeof(unsigned long)),
> (unsigned long)page->flags, page->mapping,
> page_mapcount(page), page_count(page));
> dump_stack();
> page->flags &= ~(1 << PG_lru |
> 1 << PG_private |
> 1 << PG_locked |
> 1 << PG_active |
> 1 << PG_dirty |
> 1 << PG_reclaim |
> 1 << PG_slab |
> 1 << PG_swapcache |
> 1 << PG_writeback |
> 1 << PG_buddy );
> set_page_count(page, 0);
> reset_page_mapcount(page);
> page->mapping = NULL;
> add_taint(TAINT_BAD_PAGE);
> }
>
> Question:
>
> a. what is the purpose of this function - it seems that all the
> caller of this function will continue execution as if nothing has
> happened? And the next line may process the "page" which this
> funcion has modify?
> b. what is the purpose of setting to NOT the list of PG_xxxx flags
> shown above?
IMHO, this function is called when some inconsistency is detected regarding the page structure. Since something problematic has occured, the code is just trying to do a graceful recovery by setting default values to certain page attributes. And hence the code continues as it is after calling this function (to make a note that somehing is not right).
> c. What is the purpose of the add_taint() function?
As the comment clearly indicates, this function asserts that you can't trust the integrity of the kernel anymore. This may be due to a lot of reasons such as insertion of a tainted module (unlicensed) and in this case, TAINT_BAD_PAGE. Here are the various other reasons:
TAINT_PROPRIETARY_MODULE
TAINT_FORCED_MODULE
TAINT_UNSAFE_SMP
TAINT_FORCED_RMMOD
TAINT_MACHINE_CHECK
TAINT_BAD_PAGE
TAINT_USER
TAINT_DIE
The kernel informs that it is tainted in case of OOPS / Panic etc. In case of tainted kernel due to proprietary module, kernel developers are likely suggest you to remove the tainted condition first.
Thanks,
Rajat
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