diff options
| author | Oleg Nesterov <oleg@tv-sign.ru> | 2006-03-22 00:08:47 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-03-22 07:54:03 -0800 |
| commit | a564da3964db3256069190c2ae95069143ac37fb (patch) | |
| tree | b7b9d66c1d6dde82db23222b16b0296013b1c3db /mm | |
| parent | d15c023b44e5d323f1f4130b85d29f08e43433b1 (diff) | |
[PATCH] readahead: ->prev_page can overrun the ahead window
If get_next_ra_size() does not grow fast enough, ->prev_page can overrun
the ahead window. This means the caller will read the pages from
->ahead_start + ->ahead_size to ->prev_page synchronously.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Steven Pratt <slpratt@austin.ibm.com>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/readahead.c | 26 |
1 files changed, 20 insertions, 6 deletions
diff --git a/mm/readahead.c b/mm/readahead.c index 8d6eeaaa629..57557e29498 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -52,13 +52,24 @@ static inline unsigned long get_min_readahead(struct file_ra_state *ra) return (VM_MIN_READAHEAD * 1024) / PAGE_CACHE_SIZE; } +static inline void reset_ahead_window(struct file_ra_state *ra) +{ + /* + * ... but preserve ahead_start + ahead_size value, + * see 'recheck:' label in page_cache_readahead(). + * Note: We never use ->ahead_size as rvalue without + * checking ->ahead_start != 0 first. + */ + ra->ahead_size += ra->ahead_start; + ra->ahead_start = 0; +} + static inline void ra_off(struct file_ra_state *ra) { ra->start = 0; ra->flags = 0; ra->size = 0; - ra->ahead_start = 0; - ra->ahead_size = 0; + reset_ahead_window(ra); return; } @@ -426,8 +437,7 @@ static int make_ahead_window(struct address_space *mapping, struct file *filp, * congestion. The ahead window will any way be closed * in case we failed due to excessive page cache hits. */ - ra->ahead_start = 0; - ra->ahead_size = 0; + reset_ahead_window(ra); } return ret; @@ -520,11 +530,11 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra, * If we get here we are doing sequential IO and this was not the first * occurence (ie we have an existing window) */ - if (ra->ahead_start == 0) { /* no ahead window yet */ if (!make_ahead_window(mapping, filp, ra, 0)) - goto out; + goto recheck; } + /* * Already have an ahead window, check if we crossed into it. * If so, shift windows and issue a new ahead window. @@ -536,6 +546,10 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra, ra->start = ra->ahead_start; ra->size = ra->ahead_size; make_ahead_window(mapping, filp, ra, 0); +recheck: + /* prev_page shouldn't overrun the ahead window */ + ra->prev_page = min(ra->prev_page, + ra->ahead_start + ra->ahead_size - 1); } out: |