> On Dec. 7, 2013, 9:48 a.m., Matt Jordan wrote: > > /branches/1.8/main/pbx.c, lines 4477-4491 > > <https://reviewboard.asterisk.org/r/3055/diff/4/?file=49180#file49180line4477> > > > > I don't think we need the extra lock here. > > > > The purpose of the contexts lock is to prevent changes to the dialplan > > while some portion of it is being used. In this case, > > pbx_substitute_variables will extract data from the ast_exten object e when > > it is called. > > > > Interestingly enough, variable substitution does not actually need the > > ast_exten object. pbx_substitute_variables acts as a wrapper for > > pbx_substitute_variables_helper, which is what actually does the work. > > pbx_substitute_variables_helper takes in char *. > > > > The bug here seems to be that we unlock the context lock before we > > should. Either pbx_substitute_variables should be removed and the values > > extracted in this function, or pbx_substitute_variables should be > > responsible for unlocking the contexts lock before calling the variable > > substiution function.
The pbx_substitute_* functions *can* refer to the ast_exten object's data member, as that's where the expression to evaluate is stored. This is the very nature of the fault that valgrind is exposing - e->data has been free'd because of a reload operation on another thread before a reference to it occurring during pbx_substitute_variables and functions it calls. This lock accurately and reliably (per testing) prevents this failure. An option to eliminate the need for a lock would be to rewrite pbx_substitute_variables() so that it is passed e->data instead of e, which is the only element it references (and then passes into pbx_substitute_variables_helper()). Then a copy of e->data could be put locally on stack or other allocation prior to releaseing the global contexts mutex, and then pass it to pbx_substitute_variables(). That could be more performance impacting than the lock, depending on the speed of the lock. I could run a test to determine which is the higher speed approach. > On Dec. 7, 2013, 9:48 a.m., Matt Jordan wrote: > > /branches/1.8/main/pbx.c, lines 825-828 > > <https://reviewboard.asterisk.org/r/3055/diff/4/?file=49180#file49180line825> > > > > So, as Mark alluded to, I would just remove these functions and use the > > actual calls to ast_rwlock*. > > > > The reason there is a wrapper around the contexts lock functions here > > in pbx.c is historical. At one point, there was an attempt to use > > read-write locks for the contexts lock. However, due to the recursive > > nature of some of the function calls, the locks could be obtained multiple > > times, resulting in invalid locking with r/w locks. A wrapper was provided > > in the (probably vain) hope that someday we'd be able to unravel the > > recursive calls and switch to r/w locks which - since dialplan isn't > > modified terribly often - provide some performance improvement. > > > > So, just use the direct calls :-) Agreed. I'll eliminate the extraneous functions. The ones I copied from are actually referenced from other .c's, whereas these are static to pbx.c and unnecessary. - Scott ----------------------------------------------------------- This is an automatically generated e-mail. To reply, visit: https://reviewboard.asterisk.org/r/3055/#review10328 ----------------------------------------------------------- On Dec. 6, 2013, 4:44 p.m., Scott Griepentrog wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > https://reviewboard.asterisk.org/r/3055/ > ----------------------------------------------------------- > > (Updated Dec. 6, 2013, 4:44 p.m.) > > > Review request for Asterisk Developers and Matt Jordan. > > > Bugs: AST-1179 and AST-1246 > https://issues.asterisk.org/jira/browse/AST-1179 > https://issues.asterisk.org/jira/browse/AST-1246 > > > Repository: Asterisk > > > Description > ------- > > During dialplan execution in pbx_extension_helper(), the contexts global read > lock is used prevent changes to the dialplan. This patch adds a lock between > that point and until after the extension previously found is no longer being > referenced -- after variable substitution, but before app execution. This > new lock prevents the extension's allocation from being released by module > reload when it is still being used in an expression evaluation. > > > Diffs > ----- > > /branches/1.8/main/pbx.c 403430 > > Diff: https://reviewboard.asterisk.org/r/3055/diff/ > > > Testing > ------- > > Testsuite test 'dialplan_stress' (https://reviewboard.asterisk.org/r/3056/) > created to isolate this problem and test this fix. > > > Thanks, > > Scott Griepentrog > >
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