On 05/15/2010 03:32 PM, Pete Zaitcev wrote:
A long-running tabled is virtually guaranteed to crash when it's shut
down, with the traceback like this:
Program terminated with signal 11, Segmentation fault.
#0 cldc_close (fh=0x10a71c8, copts=0x7fff2fdef780) at cldc.c:1049
1049 if (sess->expired) {
(gdb) where
#0 cldc_close (fh=0x10a71c8, copts=0x7fff2fdef780) at cldc.c:1049
#1 0x00007f8a878ed7c7 in ncld_close (fh=0x10a7790) at cldc.c:2215
#2 0x00007f8a878ed918 in ncld_sess_close (nsess=0x10a6f10) at cldc.c:2247
#3 0x0000000000406252 in cld_end () at cldu.c:701
#4 0x000000000040d6c4 in main (argc=<value optimized out>,
argv=<value optimized out>) at server.c:1980
(gdb) print *fh
$3 = {fh = 140232956496032, sess = 0x0, valid = 176}
Obviously the boolean value should not be 176.
The reason this happens is array reallocation. The API for libcldc
(used internally by ncld) returns a pointer to struct cldc_fh that
the user is expected to save. However, this structure is placed
inside a GArray. As array expands, it can be relocated in memory
and the file handle pointer is left hanging. Tabled is vulnerable
to this because 1) it keeps an open handle for the CLD file that
it locked and 2) it periodically opens and closes CLD files for
chunkservers, causing array to grow.
We observed that the indexes into the array are not the same
as file handles. Therefore, we never access elements by index
and thus it is not necessary to use an array structure.
This patch replaces array with a list, so that pointers to handle
structures can be stable.
Also, the patch frees the handles when they are closed, thus
ending the endless growth of the file handle table. This is
done in a compatible way, so handle is available to callers
of cldc_close (ncld does not need it, but it may be useful).
Although we change globally visible structures, we only replace
one ostensibly opaque pointer type (GArray) with another one
(GList), so applications need not be rebuilt.
Signed-off-by: Pete Zaitcev<zaitcev@xxxxxxxxxx>
applied
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