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authorTom Lane2016-07-07 15:28:17 +0000
committerTom Lane2016-07-07 15:28:17 +0000
commit62c8421e87b33b2e94f8a7842e1dd9aa1a286ffc (patch)
tree37754d294bd73b6ab5f210c0ae8df1a7d14ef7d3
parent60d50769b70ca5030711f70c86d7a2d3bcf34963 (diff)
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.
-rw-r--r--src/timezone/localtime.c12
1 files changed, 10 insertions, 2 deletions
diff --git a/src/timezone/localtime.c b/src/timezone/localtime.c
index 985ad56da2..a14215d6bd 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