Messages in this thread Patch in this message |  | | | Date | Wed, 31 Mar 2004 17:22:16 -0800 | | From | Andrew Morton <> | | Subject | Re: [RFC][PATCH 1/3] radix priority search tree - objrmap complexity fix |
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Andrea Arcangeli <andrea@suse.de> wrote: > > @@ -151,8 +151,11 @@ int rw_swap_page_sync(int rw, swp_entry_ > lock_page(page); > > BUG_ON(page->mapping); > - page->mapping = &swapper_space; > - page->index = entry.val; > + ret = add_to_page_cache(page, &swapper_space, entry.val, GFP_KERNEL);
Doing a __GFP_FS allocation while holding lock_page() is worrisome. It's OK if that page is private, but how do we know that the caller didn't pass us some page which is on the LRU?
The only place where I think we can deadlock is if that GFP_KERNEL allocation tries to write out the page we hold a lock on, and we hit an error running swap_writepage() and then enter handle_write_error().
This actually cannot happen because swap_writepage() can only fail if bio_alloc() fails, and that uses a mempool. But ick.
Your patch seems reasonable to run with for now, but to be totally anal about it, I'll run with the below monstrosity.
diff -puN mm/page_io.c~rw_swap_page_sync-fix mm/page_io.c --- 25/mm/page_io.c~rw_swap_page_sync-fix Wed Mar 31 16:55:44 2004 +++ 25-akpm/mm/page_io.c Wed Mar 31 17:15:31 2004 @@ -19,6 +19,7 @@ #include <linux/buffer_head.h> /* for block_sync_page() */ #include <linux/mpage.h> #include <linux/writeback.h> +#include <linux/radix-tree.h> #include <asm/pgtable.h> static struct bio * @@ -137,9 +138,11 @@ struct address_space_operations swap_aop .set_page_dirty = __set_page_dirty_nobuffers, }; +#if defined(CONFIG_SOFTWARE_SUSPEND) || defined(CONFIG_PM_DISK) + /* * A scruffy utility function to read or write an arbitrary swap page - * and wait on the I/O. + * and wait on the I/O. The caller must have a ref on the page. */ int rw_swap_page_sync(int rw, swp_entry_t entry, struct page *page) { @@ -148,11 +151,30 @@ int rw_swap_page_sync(int rw, swp_entry_ .sync_mode = WB_SYNC_ALL, }; - lock_page(page); - BUG_ON(page->mapping); - page->mapping = &swapper_space; - page->index = entry.val; + + /* + * We shouldn't perform add_to_page_cache(..., GFP_KERNEL) inside + * lock_page(), so here we do bizarre things to arrange for the page + * to be locked while ensuring that this CPU has sufficient pooled + * radix-tree nodes for a successful add_to_page_cache(). + */ + for ( ; ; ) { + ret = radix_tree_preload(GFP_KERNEL); + if (ret) + goto out; + if (TestSetPageLocked(page) == 0) + break; + radix_tree_preload_end(); + lock_page(page); + unlock_page(page); + } + ret = add_to_page_cache(page, &swapper_space, entry.val, GFP_ATOMIC); + radix_tree_preload_end(); + if (ret) { + unlock_page(page); + goto out; + } if (rw == READ) { ret = swap_readpage(NULL, page); @@ -161,8 +183,15 @@ int rw_swap_page_sync(int rw, swp_entry_ ret = swap_writepage(page, &swap_wbc); wait_on_page_writeback(page); } - page->mapping = NULL; + + lock_page(page); + remove_from_page_cache(page); + unlock_page(page); + page_cache_release(page); /* For add_to_page_cache() */ + if (ret == 0 && (!PageUptodate(page) || PageError(page))) ret = -EIO; +out: return ret; } +#endif _
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