[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>
diff --git a/mm/readahead.c b/mm/readahead.c
index 8d6eeaa..57557e2 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -52,13 +52,24 @@
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 @@
* 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 @@
* 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 @@
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: