From: Andreas Schwab <schwab@suse.de>
To: libc-alpha@sourceware.org
Subject: [PATCH] Always do locking when accessing streams (bug 15142)
Date: Wed, 13 Nov 2019 12:21:51 +0100 [thread overview]
Message-ID: <mvmpnhwvx68.fsf@suse.de> (raw)
During exit, skip files that are currently locked to avoid deadlock.
---
libio/genops.c | 54 ++++++++++++++++++++++++++------------------------
libio/libio.h | 4 ++++
libio/libioP.h | 1 -
3 files changed, 32 insertions(+), 27 deletions(-)
diff --git a/libio/genops.c b/libio/genops.c
index f871e7751b..30daa169ef 100644
--- a/libio/genops.c
+++ b/libio/genops.c
@@ -681,8 +681,8 @@ _IO_adjust_column (unsigned start, const char *line, int count)
}
libc_hidden_def (_IO_adjust_column)
-int
-_IO_flush_all_lockp (int do_lock)
+static int
+_IO_flush_all_lockp (bool skip_locked)
{
int result = 0;
FILE *fp;
@@ -695,7 +695,16 @@ _IO_flush_all_lockp (int do_lock)
for (fp = (FILE *) _IO_list_all; fp != NULL; fp = fp->_chain)
{
run_fp = fp;
- if (do_lock)
+ if (skip_locked)
+ {
+ /* Skip files that are currently locked. */
+ if (_IO_ftrylockfile (fp))
+ {
+ run_fp = NULL;
+ continue;
+ }
+ }
+ else
_IO_flockfile (fp);
if (((fp->_mode <= 0 && fp->_IO_write_ptr > fp->_IO_write_base)
@@ -706,8 +715,7 @@ _IO_flush_all_lockp (int do_lock)
&& _IO_OVERFLOW (fp, EOF) == EOF)
result = EOF;
- if (do_lock)
- _IO_funlockfile (fp);
+ _IO_funlockfile (fp);
run_fp = NULL;
}
@@ -724,7 +732,7 @@ int
_IO_flush_all (void)
{
/* We want locking. */
- return _IO_flush_all_lockp (1);
+ return _IO_flush_all_lockp (false);
}
libc_hidden_def (_IO_flush_all)
@@ -789,6 +797,14 @@ _IO_unbuffer_all (void)
for (fp = (FILE *) _IO_list_all; fp; fp = fp->_chain)
{
+ run_fp = fp;
+ /* Skip files that are currently locked. */
+ if (_IO_ftrylockfile (fp))
+ {
+ run_fp = NULL;
+ continue;
+ }
+
int legacy = 0;
#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_1)
@@ -800,18 +816,6 @@ _IO_unbuffer_all (void)
/* Iff stream is un-orientated, it wasn't used. */
&& (legacy || fp->_mode != 0))
{
-#ifdef _IO_MTSAFE_IO
- int cnt;
-#define MAXTRIES 2
- for (cnt = 0; cnt < MAXTRIES; ++cnt)
- if (fp->_lock == NULL || _IO_lock_trylock (*fp->_lock) == 0)
- break;
- else
- /* Give the other thread time to finish up its use of the
- stream. */
- __sched_yield ();
-#endif
-
if (! legacy && ! dealloc_buffers && !(fp->_flags & _IO_USER_BUF))
{
fp->_flags |= _IO_USER_BUF;
@@ -825,17 +829,15 @@ _IO_unbuffer_all (void)
if (! legacy && fp->_mode > 0)
_IO_wsetb (fp, NULL, NULL, 0);
-
-#ifdef _IO_MTSAFE_IO
- if (cnt < MAXTRIES && fp->_lock != NULL)
- _IO_lock_unlock (*fp->_lock);
-#endif
}
/* Make sure that never again the wide char functions can be
used. */
if (! legacy)
fp->_mode = -1;
+
+ _IO_funlockfile (fp);
+ run_fp = NULL;
}
#ifdef _IO_MTSAFE_IO
@@ -861,9 +863,9 @@ libc_freeres_fn (buffer_free)
int
_IO_cleanup (void)
{
- /* We do *not* want locking. Some threads might use streams but
- that is their problem, we flush them underneath them. */
- int result = _IO_flush_all_lockp (0);
+ /* We want to skip locked streams. Some threads might use streams but
+ that is their problem, we don't flush those. */
+ int result = _IO_flush_all_lockp (true);
/* We currently don't have a reliable mechanism for making sure that
C++ static destructors are executed in the correct order.
diff --git a/libio/libio.h b/libio/libio.h
index bed324e57d..3e660bd454 100644
--- a/libio/libio.h
+++ b/libio/libio.h
@@ -291,11 +291,15 @@ libc_hidden_proto (_IO_sgetn)
if (((_fp)->_flags & _IO_USER_LOCK) == 0) _IO_lock_lock (*(_fp)->_lock)
# define _IO_funlockfile(_fp) \
if (((_fp)->_flags & _IO_USER_LOCK) == 0) _IO_lock_unlock (*(_fp)->_lock)
+# define _IO_ftrylockfile(_fp) \
+ (((_fp)->_flags & _IO_USER_LOCK) == 0 ? _IO_lock_trylock (*(_fp)->_lock) : 0)
# else
# define _IO_flockfile(_fp) \
if (((_fp)->_flags & _IO_USER_LOCK) == 0) _IO_flockfile (_fp)
# define _IO_funlockfile(_fp) \
if (((_fp)->_flags & _IO_USER_LOCK) == 0) _IO_funlockfile (_fp)
+# define _IO_ftrylockfile(_fp) \
+ (((_fp)->_flags & _IO_USER_LOCK) == 0 ? _IO_ftrylockfile (_fp) : 0)
# endif
#endif /* _IO_MTSAFE_IO */
diff --git a/libio/libioP.h b/libio/libioP.h
index 3787605cfb..2187b8edbe 100644
--- a/libio/libioP.h
+++ b/libio/libioP.h
@@ -487,7 +487,6 @@ extern int _IO_new_do_write (FILE *, const char *, size_t);
extern int _IO_old_do_write (FILE *, const char *, size_t);
extern int _IO_wdo_write (FILE *, const wchar_t *, size_t);
libc_hidden_proto (_IO_wdo_write)
-extern int _IO_flush_all_lockp (int);
extern int _IO_flush_all (void);
libc_hidden_proto (_IO_flush_all)
extern int _IO_cleanup (void);
--
2.24.0
--
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."
next reply other threads:[~2019-11-13 11:22 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-13 11:21 Andreas Schwab [this message]
2019-11-21 12:25 ` [PATCH] Always do locking when accessing streams (bug 15142) Florian Weimer
2019-11-21 13:14 ` Andreas Schwab
2019-11-21 13:20 ` Florian Weimer
2019-11-21 13:27 ` Andreas Schwab
2019-11-25 13:30 ` Florian Weimer
2019-11-25 13:34 ` Andreas Schwab
2019-11-25 13:35 ` Florian Weimer
-- strict thread matches above, loose matches on Subject: below --
2018-01-30 16:58 Andreas Schwab
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