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authorPedro Alves <pedro@palves.net>2021-06-17 16:23:03 +0100
committerPedro Alves <pedro@palves.net>2021-06-17 19:39:08 +0100
commit336b30e58ae98fe66862ab8480d3f7bb885fef23 (patch)
treeb0def784a1fefc869831e11a4ec3b29edea55501 /gdbsupport
parente013d20dc73b40d4b70c4a366c9adc619503e66b (diff)
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Don't call sigtimedwait for scoped_ignore_sigttou
Because SIGTTOU is sent to the whole process instead of to a specific thread, consuming a pending SIGTTOU in the destructor of scoped_ignore_sigttou could consume a SIGTTOU signal raised due to actions done by some other thread. Simply avoid sigtimedwait in scoped_ignore_sigttou, thus plugging the race. This works because we know that when the thread writes to the terminal and the signal is blocked, the kernel does not raise the signal at all. Tested on GNU/Linux, Solaris 11 and FreeBSD. gdb/ChangeLog: yyyy-mm-dd Pedro Alves <pedro@palves.net> * scoped_ignore_signal.h (scoped_ignore_signal): Add ConsumePending template parameter. (scoped_ignore_signal::~scoped_ignore_signal): Skip calling sigtimedwait if ConsumePending is false. (scoped_ignore_sigpipe): Initialize with ConsumePending=true. * scoped_ignore_sigttou.h (scoped_ignore_sigttou) <m_ignore_signal>: Initialize with ConsumePending=false. Change-Id: I92f754dbc45c45819dce2ce68b8c067d8d5c61b1
Diffstat (limited to 'gdbsupport')
-rw-r--r--gdbsupport/scoped_ignore_signal.h18
-rw-r--r--gdbsupport/scoped_ignore_sigttou.h2
2 files changed, 14 insertions, 6 deletions
diff --git a/gdbsupport/scoped_ignore_signal.h b/gdbsupport/scoped_ignore_signal.h
index 55a921c..a14c967 100644
--- a/gdbsupport/scoped_ignore_signal.h
+++ b/gdbsupport/scoped_ignore_signal.h
@@ -25,9 +25,16 @@
/* RAII class used to ignore a signal in a scope. If sigprocmask is
supported, then the signal is only ignored by the calling thread.
Otherwise, the signal disposition is set to SIG_IGN, which affects
- the whole process. */
-
-template <int Sig>
+ the whole process. If ConsumePending is true, the destructor
+ consumes a pending Sig. SIGPIPE for example is queued on the
+ thread even if blocked at the time the pipe is written to. SIGTTOU
+ OTOH is not raised at all if the thread writing to the terminal has
+ it blocked. Because SIGTTOU is sent to the whole process instead
+ of to a specific thread, consuming a pending SIGTTOU in the
+ destructor could consume a signal raised due to actions done by
+ some other thread. */
+
+template <int Sig, bool ConsumePending>
class scoped_ignore_signal
{
public:
@@ -58,7 +65,8 @@ public:
/* If we got a pending Sig signal, consume it before
unblocking. */
- sigtimedwait (&set, nullptr, &zero_timeout);
+ if (ConsumePending)
+ sigtimedwait (&set, nullptr, &zero_timeout);
sigprocmask (SIG_UNBLOCK, &set, nullptr);
}
@@ -89,7 +97,7 @@ struct scoped_ignore_signal_nop
};
#ifdef SIGPIPE
-using scoped_ignore_sigpipe = scoped_ignore_signal<SIGPIPE>;
+using scoped_ignore_sigpipe = scoped_ignore_signal<SIGPIPE, true>;
#else
using scoped_ignore_sigpipe = scoped_ignore_signal_nop;
#endif
diff --git a/gdbsupport/scoped_ignore_sigttou.h b/gdbsupport/scoped_ignore_sigttou.h
index 1fc8f80..5695c5d 100644
--- a/gdbsupport/scoped_ignore_sigttou.h
+++ b/gdbsupport/scoped_ignore_sigttou.h
@@ -75,7 +75,7 @@ public:
DISABLE_COPY_AND_ASSIGN (scoped_ignore_sigttou);
private:
- lazy_init<scoped_ignore_signal<SIGTTOU>> m_ignore_signal;
+ lazy_init<scoped_ignore_signal<SIGTTOU, false>> m_ignore_signal;
};
#else