postgres.git / summary / log / commit / refs

commit    62c8421e87b33b2e94f8a7842e1dd9aa1a286ffc
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Thu Jul 07 15:28:17 2016 +0000

    Reduce stack space consumption in tzload().
    
    While syncing our timezone code with IANA's updates in commit 1c1a7cbd6,
    I'd chosen not to adopt the code they conditionally compile under #ifdef
    ALL_STATE.  The main thing that that drives is that the space for gmtime
    and localtime timezone definitions isn't statically allocated, but is
    malloc'd on first use.  I reasoned we didn't need that logic: we don't have
    localtime() at all, and we always initialize TimeZone to GMT so we always
    need that one.  But there is one other thing ALL_STATE does, which is to
    make tzload() malloc its transient workspace instead of just declaring it
    as a local variable.  It turns out that that local variable occupies 78K.
    Even worse is that, at least for common US timezone settings, there's a
    recursive call to parse the "posixrules" zone name, making peak stack
    consumption to select a time zone upwards of 150K.  That's an uncomfortably
    large fraction of our STACK_DEPTH_SLOP safety margin, and could result in
    outright crashes if we try to reduce STACK_DEPTH_SLOP as has been discussed
    recently.  Furthermore, this means that the postmaster's peak stack
    consumption is several times that of a backend running typical queries
    (since, except on Windows, backends inherit the timezone GUC values and
    don't ever run this code themselves unless you do SET TIMEZONE).  That's
    completely backwards from a safety perspective.
    
    Hence, adopt the ALL_STATE rather than non-ALL_STATE variant of tzload(),
    while not changing the other code aspects that symbol controls.  The
    risk of an ENOMEM error from malloc() seems less than that of a SIGSEGV
    from stack overrun.
    
    This should probably get back-patched along with 1c1a7cbd6 and followon
    fixes, whenever we decide we have enough confidence in the updates to do
    that.


 src/timezone/localtime.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/timezone/localtime.c b/src/timezone/localtime.c
index 985ad56da20..a14215d6bde 100644
--- a/src/timezone/localtime.c
+++ b/src/timezone/localtime.c
@@ -536,9 +536,17 @@ tzloadbody(char const * name, char *canonname, struct state * sp, bool doextend,
 int
 tzload(const char *name, char *canonname, struct state * sp, bool doextend)
 {
-	union local_storage ls;
+	union local_storage *lsp = malloc(sizeof *lsp);
 
-	return tzloadbody(name, canonname, sp, doextend, &ls);
+	if (!lsp)
+		return errno;
+	else
+	{
+		int			err = tzloadbody(name, canonname, sp, doextend, lsp);
+
+		free(lsp);
+		return err;
+	}
 }
 
 static bool


[parent: 60d50769b70c]