port_create race test and fix #215
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This change adds a test to the port_tests suite to trigger the port_create() race. When tested with an SMP (3) qemu instance, the race is discovered in less than twenty iterations and often much sooner.
In the current design, ports may be created with the same name because of time-of-check-time-of-use behavior. This change adds a new port magic, PORTHOLD_MAGIC, which cannot be accessed using the normal accessors. It is injected into the list upon a successful, locked search for a name. It holds the name until the allocation happens. At which point the port-hold is deleted and the real port is added while, again, under the thread lock. This change assumes using a stack-allocated port is desirable over preallocating and freeing on each port_create(). If the overhead of allocation is low, then pre-allocating the new port would be the cleanest option: (1) allocate, (2) check for collisions, (3) add to list. This fix is confirmed by the two_threads_race test completing its 256 iterations without a race. It also fixes the test to expect ERR_BUSY and to exit cleanly, as it had never completed before.
travisg
reviewed
Dec 22, 2017
app/tests/port_tests.c
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| @@ -291,6 +291,244 @@ static int ping_pong_thread(void *arg) | |||
| return __LINE__; | |||
| } | |||
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| const char *kStatusPortNames[] = { | |||
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make sure all of these are static so the compiler/linker will strip them if not building with the console.
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Reposting with that change now -- thanks!
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(Some of the functions in there can be made static too and I can make/test that for this pull or just do a second. Whichever works!)
This change makes the shared constants static as well as const-ifies shared packets.
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port_create() has a known race condition in name reservation because of the separation of name uniqueness validation and name addition. This pull request adds a test that verifies the race is reachable, fixes the race, and updates the test with slight changes to support it.