syscalls/shmctl05.c: Fix ENOSPC error

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State New
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  • syscalls/shmctl05.c: Fix ENOSPC error
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Commit Message

Xiao Yang Aug. 1, 2018, 7:34 a.m.
Running shmctl05 got the following error on some distros(e.g. RHEL7.5):
tst_safe_sysv_ipc.c:111: BROK: shmctl05.c:51: shmget(61455, 4096, 3c0) failed: ENOSPC
shmctl05.c:104: WARN: pthread_join(..., (nil)) failed: EDEADLK
tst_safe_sysv_ipc.c:111: BROK: shmctl05.c:81: shmget(61455, 4096, 3c0) failed: ENOSPC

From shmctl(2) manpage, shmctl(IPC_RMID) just marks a shm segment to
be destroyed, and the segment will only actually be destroyed after
the last process detaches it (i.e., when the shm_nattch member of the
associated structure shmid_ds is zero).  So it is possible for the
number of created shm segments to exceed the system-wide maximum number
(e.g. shmmni is 4096) if only shmctl(IPC_RMID) has been called.

From shmdt(2) manpage, a successful shmdt(2) call will decrement
the shm_nattch by one.  So we should call shmdt(2) to decrement
the shm_nattch to zero before calling shmctl(IPC_RMID).

Add shmdt(2) to ensure that all shm segments are actually destroyed.

Signed-off-by: Xiao Yang <>
 testcases/kernel/syscalls/ipc/shmctl/shmctl05.c | 2 ++
 1 file changed, 2 insertions(+)


diff --git a/testcases/kernel/syscalls/ipc/shmctl/shmctl05.c b/testcases/kernel/syscalls/ipc/shmctl/shmctl05.c
index a960cc9..0eb0776 100644
--- a/testcases/kernel/syscalls/ipc/shmctl/shmctl05.c
+++ b/testcases/kernel/syscalls/ipc/shmctl/shmctl05.c
@@ -92,6 +92,8 @@  static void do_test(void)
 				"Unexpected remap_file_pages() error");
+		/* ensure that a shm segment will actually be destroyed */
+		SAFE_SHMDT(addr);
 	tst_res(TPASS, "didn't crash");