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authorRich Felker <dalias@aerifal.cx>2011-03-24 14:18:00 -0400
committerRich Felker <dalias@aerifal.cx>2011-03-24 14:18:00 -0400
commitb470030f839a375e5030ec9d44903ef7581c15a2 (patch)
tree462b1df89a3ea45bcf50b9d0a844472576ed6585 /src/select/pselect.c
parent095820016689dfdc9141f477a86de22054c86078 (diff)
downloadmusl-b470030f839a375e5030ec9d44903ef7581c15a2.tar.gz
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overhaul cancellation to fix resource leaks and dangerous behavior with signals
this commit addresses two issues:

1. a race condition, whereby a cancellation request occurring after a
syscall returned from kernelspace but before the subsequent
CANCELPT_END would cause cancellable resource-allocating syscalls
(like open) to leak resources.

2. signal handlers invoked while the thread was blocked at a
cancellation point behaved as if asynchronous cancellation mode wer in
effect, resulting in potentially dangerous state corruption if a
cancellation request occurs.

the glibc/nptl implementation of threads shares both of these issues.

with this commit, both are fixed. however, cancellation points
encountered in a signal handler will not be acted upon if the signal
was received while the thread was already at a cancellation point.
they will of course be acted upon after the signal handler returns, so
in real-world usage where signal handlers quickly return, it should
not be a problem. it's possible to solve this problem too by having
sigaction() wrap all signal handlers with a function that uses a
pthread_cleanup handler to catch cancellation, patch up the saved
context, and return into the cancellable function that will catch and
act upon the cancellation. however that would be a lot of complexity
for minimal if any benefit...
Diffstat (limited to 'src/select/pselect.c')
-rw-r--r--src/select/pselect.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/src/select/pselect.c b/src/select/pselect.c
index 63ea0695..155a6eb0 100644
--- a/src/select/pselect.c
+++ b/src/select/pselect.c
@@ -10,6 +10,7 @@ int pselect(int n, fd_set *rfds, fd_set *wfds, fd_set *efds, const struct timesp
 	if (ts) ts_tmp = *ts;
 	CANCELPT_BEGIN;
 	r = syscall(SYS_pselect6, n, rfds, wfds, efds, ts ? &ts_tmp : 0, data);
+	CANCELPT_TRY;
 	CANCELPT_END;
 	return r;
 }