BUG/MINOR: pools: don't mark the thread harmless if already isolated

Commit 85b2cae63 ("MINOR: pools: make the thread harmless during the
mmap/munmap syscalls") was used to relax the pressure experienced by
other threads when running in debug mode with UAF enabled. It places
a pair of thread_harmless_now()/thread_harmless_end() around the call
to mmap(), assuming callers are not sensitive to parallel activity.
But there are a few cases like "show sess all" where this happens in
isolated threads, and marking the thread as harmless there is a very
bad idea, even worse when arriving to thread_harmless_end() which loops
forever.

Let's only do that when the thread is not isolated. No backport is
needed as the patch above was only in 2.1-dev.

diff --git a/include/common/memory.h b/include/common/memory.h
index 3283d2be1e58fa4c662450cdc7798ebb9a7cbd83..ae1ad22977ac766b514b5ccd30e377d29e5a8aef 100644 (file)
--- a/include/common/memory.h
+++ b/include/common/memory.h
@@ -416,9 +416,12 @@ static inline void pool_free_area(void *area, size_t __maybe_unused size)
 static inline void *pool_alloc_area(size_t size)
 {
        size_t pad = (4096 - size) & 0xFF0;
+       int isolated;
        void *ret;
 
-       thread_harmless_now();
+       isolated = thread_isolated();
+       if (!isolated)
+               thread_harmless_now();
        ret = mmap(NULL, (size + 4095) & -4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
        if (ret != MAP_FAILED) {
                /* let's dereference the page before returning so that the real
@@ -431,7 +434,8 @@ static inline void *pool_alloc_area(size_t size)
        } else {
                ret = NULL;
        }
-       thread_harmless_end();
+       if (!isolated)
+               thread_harmless_end();
        return ret;
 }