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Subject[PATCH 3.18 01/46] kernel/acct.c: fix the acct->needcheck check in check_free_space()
3.18-stable review patch.  If anyone has any objections, please let me know.


From: Oleg Nesterov <>

commit 4d9570158b6260f449e317a5f9ed030c2504a615 upstream.

As Tsukada explains, the time_is_before_jiffies(acct->needcheck) check
is very wrong, we need time_is_after_jiffies() to make sys_acct() work.

Ignoring the overflows, the code should "goto out" if needcheck >
jiffies, while currently it checks "needcheck < jiffies" and thus in the
likely case check_free_space() does nothing until jiffies overflow.

In particular this means that sys_acct() is simply broken, acct_on()
sets acct->needcheck = jiffies and expects that check_free_space()
should set acct->active = 1 after the free-space check, but this won't
happen if jiffies increments in between.

This was broken by commit 32dc73086015 ("get rid of timer in
kern/acct.c") in 2011, then another (correct) commit 795a2f22a8ea
("acct() should honour the limits from the very beginning") made the
problem more visible.

Fixes: 32dc73086015 ("get rid of timer in kern/acct.c")
Reported-by: TSUKADA Koutaro <>
Suggested-by: TSUKADA Koutaro <>
Signed-off-by: Oleg Nesterov <>
Cc: Al Viro <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Greg Kroah-Hartman <>

kernel/acct.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -96,7 +96,7 @@ static int check_free_space(struct bsd_a
struct kstatfs sbuf;

- if (time_is_before_jiffies(acct->needcheck))
+ if (time_is_after_jiffies(acct->needcheck))
goto out;

/* May block */

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