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Re: [PATCH 4/5] Fix deadlock in _int_free consistency check
On Okt 12 2017, Wilco Dijkstra <Wilco.Dijkstra@arm.com> wrote:
> Andreas Schwab wrote:
>
>> diff --git a/malloc/malloc.c b/malloc/malloc.c
>> index c00df205c6004ee5b5d0aee9ffd5130b3c8f9e9f..f4f44400d120188c4d0bece996380e04b35c8fac 100644
>> --- a/malloc/malloc.c
>> +++ b/malloc/malloc.c
>> @@ -4168,15 +4168,14 @@ _int_free (mstate av, mchunkptr p, int have_lock)
>> >= av->system_mem, 0))
>> {
>> /* We might not have a lock at this point and concurrent modifications
>> - of system_mem might have let to a false positive. Redo the test
>> - after getting the lock. */
>> - if (!have_lock
>> - || ({ __libc_lock_lock (av->mutex);
>> - chunksize_nomask (chunk_at_offset (p, size)) <= 2 * SIZE_SZ
>> - || chunksize (chunk_at_offset (p, size)) >= av->system_mem;
>> - }))
>> + of system_mem might result in a false positive. Redo the test after
>> + getting the lock. */
>> + if (!have_lock)
>> + __libc_lock_lock (av->mutex);
>> + if (chunksize_nomask (chunk_at_offset (p, size)) <= 2 * SIZE_SZ
>> + || chunksize (chunk_at_offset (p, size)) >= av->system_mem)
>
>> There is no need to redo the tests if we had the lock.
>
> Well I guess an alternative is to do:
>
> if (have_lock)
> print error
> else
> {
> lock
> repeat test and print error
> unlock
> }
No, you can just test have_lock again, and skip the redo if set. Still
much clearer than the original layout.
Andreas.
--
Andreas Schwab, SUSE Labs, schwab@suse.de
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