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Call rcu_barrier() in the isc_mem_destroy() just once

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The previous work in this area was led by the belief that we might be
calling call_rcu() from within call_rcu() callbacks.  After carefully
checking all the current callback, it became evident that this is not
the case and the problem isn't enough rcu_barrier() calls, but something
entirely else.

Call the rcu_barrier() just once as that's enough and the multiple
rcu_barrier() calls will not hide the real problem anymore, so we can
find it.
This commit is contained in:
Ondřej Surý 2024-07-10 18:50:33 +02:00
parent 96ccd962b7
commit 13941c8ca7
1 changed files with 1 additions and 39 deletions
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40
lib/isc/mem.c
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@ -13,7 +13,6 @@
/*! \file */
#include <errno.h>
#include <inttypes.h>
#include <limits.h>
#include <stdbool.h>
@ -191,9 +190,6 @@ static void
print_active(isc_mem_t *ctx, FILE *out);
#endif /* ISC_MEM_TRACKLINES */
static void
isc__mem_rcu_barrier(isc_mem_t *ctx);
#if ISC_MEM_TRACKLINES
/*!
* mctx must not be locked.
@ -587,7 +583,6 @@ isc__mem_detach(isc_mem_t **ctxp FLARG) {
ctx, file, line);
}
#endif
isc__mem_rcu_barrier(ctx);
destroy(ctx);
}
}
@ -616,39 +611,6 @@ isc__mem_putanddetach(isc_mem_t **ctxp, void *ptr, size_t size,
isc__mem_detach(&ctx FLARG_PASS);
}
static void
isc__mem_rcu_barrier(isc_mem_t *ctx) {
/*
* wait for asynchronous memory reclamation to complete
* before checking for memory leaks.
*
* Because rcu_barrier() needs to be called as many times
* as the number of nested call_rcu() calls (call_rcu()
* calls made from call_rcu thread), and currently there's
* no mechanism to detect whether there are more call_rcu
* callbacks scheduled, we simply call the rcu_barrier()
* until there's no progression in the memory freed.
*
* The overhead is negligible and it prevents rare assertion failures
* caused by the check for memory leaks below.
*/
size_t inuse;
uint_fast32_t references;
for (inuse = atomic_load(&ctx->inuse),
references = isc_refcount_current(&ctx->references);
inuse > 0 || references > 1; inuse = atomic_load(&ctx->inuse),
references = isc_refcount_current(&ctx->references))
{
rcu_barrier();
if (inuse == atomic_load(&ctx->inuse) &&
references == isc_refcount_current(&ctx->references))
{
break;
}
}
}
void
isc__mem_destroy(isc_mem_t **ctxp FLARG) {
isc_mem_t *ctx = NULL;
@ -663,7 +625,7 @@ isc__mem_destroy(isc_mem_t **ctxp FLARG) {
ctx = *ctxp;
*ctxp = NULL;
isc__mem_rcu_barrier(ctx);
rcu_barrier();
#if ISC_MEM_TRACKLINES
if ((ctx->debugging & ISC_MEM_DEBUGTRACE) != 0) {