FreeChainXenon/binutils-gdb
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Don't call sigtimedwait for scoped_ignore_sigttou

Browse source 
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
This commit is contained in:
Pedro Alves 2021-06-17 16:23:03 +01:00
parent e013d20dc7
commit 336b30e58a
3 changed files with 23 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

10
gdb/ChangeLog
View file

@ -1,3 +1,13 @@
2021-06-17 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.
2021-06-17 Pedro Alves <pedro@palves.net>
* Makefile.in (SELFTESTS_SRCS): Add

16
gdbsupport/scoped_ignore_signal.h
View file

@ -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. */
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>
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

2
gdbsupport/scoped_ignore_sigttou.h
View file

@ -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