| H A D | ccid.c | diff 8ed030dd0aa400d18c63861c2c6deb7c38f4edde Mon Feb 01 03:12:19 CET 2010 Gerrit Renker <gerrit@erg.abdn.ac.uk> dccp: fix bug in cache allocation
This fixes a bug introduced in commit de4ef86cfce60d2250111f34f8a084e769f23b16
("dccp: fix dccp rmmod when kernel configured to use slub", 17 Jan): the
vsnprintf used sizeof(slab_name_fmt), which became truncated to 4 bytes, since
slab_name_fmt is now a 4-byte pointer and no longer a 32-character array.
This lead to error messages such as
FATAL: Error inserting dccp: No buffer space available
>> kernel: [ 1456.341501] kmem_cache_create: duplicate cache cci
generated due to the truncation after the 3rd character.
Fixed for the moment by introducing a symbolic constant. Tested to fix the bug.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff de4ef86cfce60d2250111f34f8a084e769f23b16 Sun Jan 17 18:16:12 CET 2010 Neil Horman <nhorman@tuxdriver.com> dccp: fix dccp rmmod when kernel configured to use slub
Hey all-
I was tinkering with dccp recently and noticed that I BUG halted the
kernel when I rmmod-ed the dccp module. The bug halt occured because the page
that I passed to kfree failed the PageCompound and PageSlab test in the slub
implementation of kfree. I tracked the problem down to the following set of
events:
1) dccp, unlike all other uses of kmem_cache_create, allocates a string
dynamically when registering a slab cache. This allocated string is freed when
the cache is destroyed.
2) Normally, (1) is not an issue, but when Slub is in use, it is possible that
caches are 'merged'. This process causes multiple caches of simmilar
configuration to use the same cache data structure. When this happens, the new
name of the cache is effectively dropped.
3) (2) results in kmem_cache_name returning an ambigous value (i.e.
ccid_kmem_cache_destroy, which uses this fuction to retrieve the name pointer
for freeing), is no longer guaranteed that the string it assigned is what is
returned.
4) If such merge event occurs, ccid_kmem_cache_destroy frees the wrong pointer,
which trips over the BUG in the slub implementation of kfree (since its likely
not a slab allocation, but rather a pointer into the static string table
section.
So, what to do about this. At first blush this is pretty clearly a leak in the
information that slub owns, and as such a slub bug. Unfortunately, theres no
really good way to fix it, without exposing slub specific implementation details
to the generic slab interface. Also, even if we could fix this in slub cleanly,
I think the RCU free option would force us to do lots of string duplication, not
only in slub, but in every slab allocator. As such, I'd like to propose this
solution. Basically, I just move the storage for the kmem cache name to the
ccid_operations structure. In so doing, we don't have to do the kstrdup or
kfree when we allocate/free the various caches for dccp, and so we avoid the
problem, by storing names with static memory, rather than heap, the way all
other calls to kmem_cache_create do.
I've tested this out myself here, and it solves the problem quite well.
Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
|
| H A D | ccid.h | diff 8ed030dd0aa400d18c63861c2c6deb7c38f4edde Mon Feb 01 03:12:19 CET 2010 Gerrit Renker <gerrit@erg.abdn.ac.uk> dccp: fix bug in cache allocation
This fixes a bug introduced in commit de4ef86cfce60d2250111f34f8a084e769f23b16
("dccp: fix dccp rmmod when kernel configured to use slub", 17 Jan): the
vsnprintf used sizeof(slab_name_fmt), which became truncated to 4 bytes, since
slab_name_fmt is now a 4-byte pointer and no longer a 32-character array.
This lead to error messages such as
FATAL: Error inserting dccp: No buffer space available
>> kernel: [ 1456.341501] kmem_cache_create: duplicate cache cci
generated due to the truncation after the 3rd character.
Fixed for the moment by introducing a symbolic constant. Tested to fix the bug.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff de4ef86cfce60d2250111f34f8a084e769f23b16 Sun Jan 17 18:16:12 CET 2010 Neil Horman <nhorman@tuxdriver.com> dccp: fix dccp rmmod when kernel configured to use slub
Hey all-
I was tinkering with dccp recently and noticed that I BUG halted the
kernel when I rmmod-ed the dccp module. The bug halt occured because the page
that I passed to kfree failed the PageCompound and PageSlab test in the slub
implementation of kfree. I tracked the problem down to the following set of
events:
1) dccp, unlike all other uses of kmem_cache_create, allocates a string
dynamically when registering a slab cache. This allocated string is freed when
the cache is destroyed.
2) Normally, (1) is not an issue, but when Slub is in use, it is possible that
caches are 'merged'. This process causes multiple caches of simmilar
configuration to use the same cache data structure. When this happens, the new
name of the cache is effectively dropped.
3) (2) results in kmem_cache_name returning an ambigous value (i.e.
ccid_kmem_cache_destroy, which uses this fuction to retrieve the name pointer
for freeing), is no longer guaranteed that the string it assigned is what is
returned.
4) If such merge event occurs, ccid_kmem_cache_destroy frees the wrong pointer,
which trips over the BUG in the slub implementation of kfree (since its likely
not a slab allocation, but rather a pointer into the static string table
section.
So, what to do about this. At first blush this is pretty clearly a leak in the
information that slub owns, and as such a slub bug. Unfortunately, theres no
really good way to fix it, without exposing slub specific implementation details
to the generic slab interface. Also, even if we could fix this in slub cleanly,
I think the RCU free option would force us to do lots of string duplication, not
only in slub, but in every slab allocator. As such, I'd like to propose this
solution. Basically, I just move the storage for the kmem cache name to the
ccid_operations structure. In so doing, we don't have to do the kstrdup or
kfree when we allocate/free the various caches for dccp, and so we avoid the
problem, by storing names with static memory, rather than heap, the way all
other calls to kmem_cache_create do.
I've tested this out myself here, and it solves the problem quite well.
Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
|