git: 85d028223bc2 - main - libthr malloc: support recursion on thr_malloc_umtx.

[Konstantin Belousov]

The branch main has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=85d028223bc2768651f4d44881644ceb5dc2a664

commit 85d028223bc2768651f4d44881644ceb5dc2a664
Author:     Konstantin Belousov <kib at FreeBSD.org>
AuthorDate: 2021-01-12 09:02:37 +0000
Commit:     Konstantin Belousov <kib at FreeBSD.org>
CommitDate: 2021-01-12 10:45:44 +0000

    libthr malloc: support recursion on thr_malloc_umtx.
    
    One possible way the recursion can happen is during fork: suppose
    that fork is called from early code that did not triggered
    jemalloc(3) initialization yet. Then we lock thr_malloc lock, and
    call malloc_prefork() that might require initialization of jemalloc
    pthread_mutexes, calling into libthr malloc. It is safe to allow
    recursion for this occurence.
    
    PR:     252579
    Reported by:    Vasily Postnicov <shamaz.mazum at gmail.com>
    MFC after:      1 week
    Sponsored by:   The FreeBSD Foundation
---
 lib/libthr/thread/thr_malloc.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/lib/libthr/thread/thr_malloc.c b/lib/libthr/thread/thr_malloc.c
index 2f1c81142942..80a81f9c6c27 100644
--- a/lib/libthr/thread/thr_malloc.c
+++ b/lib/libthr/thread/thr_malloc.c
@@ -41,6 +41,7 @@ int npagesizes;
 size_t *pagesizes;
 static size_t pagesizes_d[2];
 static struct umutex thr_malloc_umtx;
+static u_int thr_malloc_umtx_level;
 
 void
 __thr_malloc_init(void)
@@ -60,11 +61,16 @@ __thr_malloc_init(void)
 static void
 thr_malloc_lock(struct pthread *curthread)
 {
+	uint32_t curtid;
 
 	if (curthread == NULL)
 		return;
 	curthread->locklevel++;
-	_thr_umutex_lock(&thr_malloc_umtx, TID(curthread));
+	curtid = TID(curthread);
+	if ((uint32_t)thr_malloc_umtx.m_owner == curtid)
+		thr_malloc_umtx_level++;
+	else
+		_thr_umutex_lock(&thr_malloc_umtx, curtid);
 }
 
 static void
@@ -73,7 +79,10 @@ thr_malloc_unlock(struct pthread *curthread)
 
 	if (curthread == NULL)
 		return;
-	_thr_umutex_unlock(&thr_malloc_umtx, TID(curthread));
+	if (thr_malloc_umtx_level > 0)
+		thr_malloc_umtx_level--;
+	else
+		_thr_umutex_unlock(&thr_malloc_umtx, TID(curthread));
 	curthread->locklevel--;
 	_thr_ast(curthread);
 }