git: 819999651131 - stable/12 - sbuf(9): Add NOWAIT dynamic buffer extension mode
Warner Losh
imp at FreeBSD.org
Fri Jul 16 17:46:44 UTC 2021
The branch stable/12 has been updated by imp:
URL: https://cgit.FreeBSD.org/src/commit/?id=81999965113107eb9cecc217a4f496dd78c1ca3a
commit 81999965113107eb9cecc217a4f496dd78c1ca3a
Author: Conrad Meyer <cem at FreeBSD.org>
AuthorDate: 2019-08-07 19:23:07 +0000
Commit: Warner Losh <imp at FreeBSD.org>
CommitDate: 2021-07-16 17:43:55 +0000
sbuf(9): Add NOWAIT dynamic buffer extension mode
The goal is to avoid some kinds of low-memory deadlock when formatting
heap-allocated buffers.
Reviewed by: vangyzen
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D21015
(cherry picked from commit 71db411eb627601a5f9a3464f88d75741927ce60)
---
share/man/man9/sbuf.9 | 11 +++++++++--
sys/kern/subr_sbuf.c | 16 +++++++++-------
sys/sys/sbuf.h | 1 +
3 files changed, 19 insertions(+), 9 deletions(-)
diff --git a/share/man/man9/sbuf.9 b/share/man/man9/sbuf.9
index 519e801e4868..4184f77631a7 100644
--- a/share/man/man9/sbuf.9
+++ b/share/man/man9/sbuf.9
@@ -25,7 +25,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd August 26, 2020
+.Dd July 12, 2021
.Dt SBUF 9
.Os
.Sh NAME
@@ -278,7 +278,14 @@ as a record boundary marker that will be used during drain operations to avoid
records being split.
If a record grows sufficiently large such that it fills the
.Fa sbuf
-and therefore cannot be drained without being split, an error of EDEADLK is set.
+and therefore cannot be drained without being split, an error of
+.Er EDEADLK
+is set.
+.It Dv SBUF_NOWAIT
+Indicates that attempts to extend the storage buffer should fail in low memory
+conditions, like
+.Xr malloc 9
+.Dv M_NOWAIT .
.El
.Pp
Note that if
diff --git a/sys/kern/subr_sbuf.c b/sys/kern/subr_sbuf.c
index 03f7b1e94c51..4a046cc41787 100644
--- a/sys/kern/subr_sbuf.c
+++ b/sys/kern/subr_sbuf.c
@@ -56,11 +56,11 @@ __FBSDID("$FreeBSD$");
#ifdef _KERNEL
static MALLOC_DEFINE(M_SBUF, "sbuf", "string buffers");
-#define SBMALLOC(size) malloc(size, M_SBUF, M_WAITOK|M_ZERO)
+#define SBMALLOC(size, flags) malloc(size, M_SBUF, (flags) | M_ZERO)
#define SBFREE(buf) free(buf, M_SBUF)
#else /* _KERNEL */
#define KASSERT(e, m)
-#define SBMALLOC(size) calloc(1, size)
+#define SBMALLOC(size, flags) calloc(1, size)
#define SBFREE(buf) free(buf)
#endif /* _KERNEL */
@@ -77,6 +77,8 @@ static MALLOC_DEFINE(M_SBUF, "sbuf", "string buffers");
#define SBUF_NULINCLUDED(s) ((s)->s_flags & SBUF_INCLUDENUL)
#define SBUF_ISDRAINTOEOR(s) ((s)->s_flags & SBUF_DRAINTOEOR)
#define SBUF_DODRAINTOEOR(s) (SBUF_ISSECTION(s) && SBUF_ISDRAINTOEOR(s))
+#define SBUF_MALLOCFLAG(s) \
+ (((s)->s_flags & SBUF_NOWAIT) ? M_NOWAIT : M_WAITOK)
/*
* Set / clear flags
@@ -171,7 +173,7 @@ sbuf_extend(struct sbuf *s, int addlen)
if (!SBUF_CANEXTEND(s))
return (-1);
newsize = sbuf_extendsize(s->s_size + addlen);
- newbuf = SBMALLOC(newsize);
+ newbuf = SBMALLOC(newsize, SBUF_MALLOCFLAG(s));
if (newbuf == NULL)
return (-1);
memcpy(newbuf, s->s_buf, s->s_size);
@@ -198,7 +200,7 @@ sbuf_newbuf(struct sbuf *s, char *buf, int length, int flags)
s->s_size = length;
s->s_buf = buf;
- if ((s->s_flags & SBUF_AUTOEXTEND) == 0) {
+ if (!SBUF_CANEXTEND(s)) {
KASSERT(s->s_size >= SBUF_MINSIZE,
("attempt to create an sbuf smaller than %d bytes",
SBUF_MINSIZE));
@@ -207,10 +209,10 @@ sbuf_newbuf(struct sbuf *s, char *buf, int length, int flags)
if (s->s_buf != NULL)
return (s);
- if ((flags & SBUF_AUTOEXTEND) != 0)
+ if (SBUF_CANEXTEND(s))
s->s_size = sbuf_extendsize(s->s_size);
- s->s_buf = SBMALLOC(s->s_size);
+ s->s_buf = SBMALLOC(s->s_size, SBUF_MALLOCFLAG(s));
if (s->s_buf == NULL)
return (NULL);
SBUF_SETFLAG(s, SBUF_DYNAMIC);
@@ -235,7 +237,7 @@ sbuf_new(struct sbuf *s, char *buf, int length, int flags)
if (s != NULL)
return (sbuf_newbuf(s, buf, length, flags));
- s = SBMALLOC(sizeof(*s));
+ s = SBMALLOC(sizeof(*s), (flags & SBUF_NOWAIT) ? M_NOWAIT : M_WAITOK);
if (s == NULL)
return (NULL);
if (sbuf_newbuf(s, buf, length, flags) == NULL) {
diff --git a/sys/sys/sbuf.h b/sys/sys/sbuf.h
index 1927996c8f38..9ef9bad7d9be 100644
--- a/sys/sys/sbuf.h
+++ b/sys/sys/sbuf.h
@@ -52,6 +52,7 @@ struct sbuf {
#define SBUF_AUTOEXTEND 0x00000001 /* automatically extend buffer */
#define SBUF_INCLUDENUL 0x00000002 /* nulterm byte is counted in len */
#define SBUF_DRAINTOEOR 0x00000004 /* use section 0 as drain EOR marker */
+#define SBUF_NOWAIT 0x00000008 /* Extend with non-blocking malloc */
#define SBUF_USRFLAGMSK 0x0000ffff /* mask of flags the user may specify */
#define SBUF_DYNAMIC 0x00010000 /* s_buf must be freed */
#define SBUF_FINISHED 0x00020000 /* set by sbuf_finish() */
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