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make mapRetrieveWO take exclusive lock

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Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I4929bbc3490350fc4c57e909109d2ec36eb0359c
This commit is contained in:
Maciej Żenczykowski 2024-06-14 13:55:09 -07:00
commit 7eb7d67279
2 changed files with 6 additions and 4 deletions
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5
netd/BpfHandler.cpp
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@ -204,7 +204,7 @@ static void mapLockTest(void) {
const char * const m1 = BPF_NETD_PATH "map_netd_lock_array_test_map";
const char * const m2 = BPF_NETD_PATH "map_netd_lock_hash_test_map";
unique_fd fd0(bpf::mapRetrieveExclusiveRW(m1)); if (!fd0.ok()) abort();
unique_fd fd0(bpf::mapRetrieveExclusiveRW(m1)); if (!fd0.ok()) abort(); // grabs exclusive lock
unique_fd fd1(bpf::mapRetrieveExclusiveRW(m2)); if (!fd1.ok()) abort(); // no conflict with fd0
unique_fd fd2(bpf::mapRetrieveExclusiveRW(m2)); if ( fd2.ok()) abort(); // busy due to fd1
@ -215,6 +215,9 @@ static void mapLockTest(void) {
unique_fd fd6(bpf::mapRetrieveRW(m2)); if (!fd6.ok()) abort(); // now ok
unique_fd fd7(bpf::mapRetrieveRO(m2)); if (!fd7.ok()) abort(); // no lock taken
unique_fd fd8(bpf::mapRetrieveExclusiveRW(m2)); if ( fd8.ok()) abort(); // busy due to fd6
fd0.reset(); // releases exclusive lock
unique_fd fd9(bpf::mapRetrieveWO(m1)); if (!fd9.ok()) abort(); // grabs exclusive lock
}
Status BpfHandler::initMaps() {

5
staticlibs/native/bpf_syscall_wrappers/include/BpfSyscallWrappers.h
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@ -175,10 +175,9 @@ inline int mapRetrieveRO(const char* pathname) {
}
// WARNING: it's impossible to grab a shared (ie. read) lock on a write-only fd,
// so only use this if you don't care about locking, ie. never use
// mapRetrieveExclusiveRW() on the same map (ie. pathname).
// so we instead choose to grab an exclusive (ie. write) lock.
inline int mapRetrieveWO(const char* pathname) {
return bpfFdGet(pathname, BPF_F_WRONLY);
return bpfLock(bpfFdGet(pathname, BPF_F_WRONLY), F_WRLCK);
}
inline int retrieveProgram(const char* pathname) {