From: Neil Horman <nhorman@xxxxxxxxxxxxx>
Date: Thu, 18 Feb 2016 10:02:04 -0500
> Dmitry Vyukov noted recently that the sctp_port_hashtable had an error in
> its size computation, observing that the current method never guaranteed
> that the hashsize (measured in number of entries) would be a power of two,
> which the input hash function for that table requires. The root cause of
> the problem is that two values need to be computed (one, the allocation
> order of the storage requries, as passed to __get_free_pages, and two the
> number of entries for the hash table). Both need to be ^2, but for
> different reasons, and the existing code is simply computing one order
> value, and using it as the basis for both, which is wrong (i.e. it assumes
> that ((1<<order)*PAGE_SIZE)/sizeof(bucket) is still ^2 when its not).
>
> To fix this, we change the logic slightly. We start by computing a goal
> allocation order (which is limited by the maximum size hash table we want
> to support. Then we attempt to allocate that size table, decreasing the
> order until a successful allocation is made. Then, with the resultant
> successful order we compute the number of buckets that hash table supports,
> which we then round down to the nearest power of two, giving us the number
> of entries the table actually supports.
>
> I've tested this locally here, using non-debug and spinlock-debug kernels,
> and the number of entries in the hashtable consistently work out to be
> powers of two in all cases.
>
> Signed-off-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
This needs some work:
In file included from include/linux/list.h:8:0,
from include/linux/module.h:9, from net/sctp/protocol.c:44:
net/sctp/protocol.c: In function ʽsctp_initʼ:
include/linux/kernel.h:752:17: warning: comparison of distinct
pointer types lacks a cast (void) (&_min1 == &_min2); \ ^
net/sctp/protocol.c:1431:10: note: in expansion of macro ʽminʼ order
= min(order, max_entry_order); ^ In file included from
include/linux/printk.h:6:0, from include/linux/kernel.h:13, from
include/linux/list.h:8, from include/linux/module.h:9, from
net/sctp/protocol.c:44:
include/linux/kern_levels.h:4:18: warning: format ʽ%dʼ expects argument of type ʽintʼ, but argument 3 has type ʽlong unsigned intʼ [-Wformat=]
#define KERN_SOH "\001" /* ASCII Start Of Header */
^
include/linux/kern_levels.h:13:19: note: in expansion of macro ʽKERN_SOHʼ
#define KERN_INFO KERN_SOH "6" /* informational */
^
include/linux/printk.h:259:9: note: in expansion of macro ʽKERN_INFOʼ
printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)
^
net/sctp/protocol.c:1484:2: note: in expansion of macro ʽpr_infoʼ
pr_info("Hash tables configured (bind %d/%d)\n", sctp_port_hashsize,
^
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