um: Memory corruption on startup

The reverse case of this race (you must msync before read) is
well known. This is the not so common one.

It can be triggered only on systems which do a lot of task
switching and only at UML startup. If you are starting 200+ UMLs
~ 0.5% will always die without this fix.

Signed-off-by: Anton Ivanov <antivano@cisco.com>
[rw: minor whitespace fixes]
Signed-off-by: Richard Weinberger <richard@nod.at>

diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index 75298d3358e7f3d2c7ff4e2b2c5ed8b81a8dca6d..08eec0b691b061ade61d8f9df7258ea4bee49f42 100644 (file)
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -136,6 +136,7 @@ extern int os_ioctl_generic(int fd, unsigned int cmd, unsigned long arg);
 extern int os_get_ifname(int fd, char *namebuf);
 extern int os_set_slip(int fd);
 extern int os_mode_fd(int fd, int mode);
+extern int os_fsync_file(int fd);
 
 extern int os_seek_file(int fd, unsigned long long offset);
 extern int os_open_file(const char *file, struct openflags flags, int mode);

diff --git a/arch/um/kernel/physmem.c b/arch/um/kernel/physmem.c
index f116db15d4028217767f2a7f51dc0bba38b151a9..30fdd5d0067b26c91fb8c831da5a1d4008c79e22 100644 (file)
--- a/arch/um/kernel/physmem.c
+++ b/arch/um/kernel/physmem.c
@@ -103,6 +103,7 @@ void __init setup_physmem(unsigned long start, unsigned long reserve_end,
         */
        os_seek_file(physmem_fd, __pa(&__syscall_stub_start));
        os_write_file(physmem_fd, &__syscall_stub_start, PAGE_SIZE);
+       os_fsync_file(physmem_fd);
 
        bootmap_size = init_bootmem(pfn, pfn + delta);
        free_bootmem(__pa(reserve_end) + bootmap_size,

diff --git a/arch/um/os-Linux/file.c b/arch/um/os-Linux/file.c
index 07a750197bb09d3b5ce59b631aed874d58603386..08d90fba952c3e1ba07e0fa488012aa26a6b473c 100644 (file)
--- a/arch/um/os-Linux/file.c
+++ b/arch/um/os-Linux/file.c
@@ -237,6 +237,12 @@ void os_close_file(int fd)
 {
        close(fd);
 }
+int os_fsync_file(int fd)
+{
+       if (fsync(fd) < 0)
+           return -errno;
+       return 0;
+}
 
 int os_seek_file(int fd, unsigned long long offset)
 {