This is a note to let you know that I've just added the patch titled
powerpc/pseries/vas: Hold mmap_mutex after mmap lock during window close
to the 6.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
powerpc-pseries-vas-hold-mmap_mutex-after-mmap-lock-.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit bf2fb3cbff40cf4d6375d9d8481592a20bfa3ff3
Author: Haren Myneni <haren@xxxxxxxxxxxxx>
Date: Sun Jul 16 03:05:06 2023 -0700
powerpc/pseries/vas: Hold mmap_mutex after mmap lock during window close
[ Upstream commit b59c9dc4d9d47b3c4572d826603fde507055b656 ]
Commit 8ef7b9e1765a ("powerpc/pseries/vas: Close windows with DLPAR
core removal") unmaps the window paste address and issues HCALL to
close window in the hypervisor for migration or DLPAR core removal
events. So holds mmap_mutex and then mmap lock before unmap the
paste address. But if the user space issue mmap paste address at
the same time with the migration event, coproc_mmap() is called
after holding the mmap lock which can trigger deadlock when trying
to acquire mmap_mutex in coproc_mmap().
t1: mmap() call to mmap t2: Migration event
window paste address
do_mmap2() migration_store()
ksys_mmap_pgoff() pseries_migrate_partition()
vm_mmap_pgoff() vas_migration_handler()
Acquire mmap lock reconfig_close_windows()
do_mmap() lock mmap_mutex
mmap_region() Acquire mmap lock
call_mmap() //Wait for mmap lock
coproc_mmap() unmap vma
lock mmap_mutex update window status
//wait for mmap_mutex Release mmap lock
mmap vma unlock mmap_mutex
update window status
unlock mmap_mutex
...
Release mmap lock
Fix this deadlock issue by holding mmap lock first before mmap_mutex
in reconfig_close_windows().
Fixes: 8ef7b9e1765a ("powerpc/pseries/vas: Close windows with DLPAR core removal")
Signed-off-by: Haren Myneni <haren@xxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://msgid.link/20230716100506.7833-1-haren@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/powerpc/platforms/pseries/vas.c b/arch/powerpc/platforms/pseries/vas.c
index 9a44a98ba3420..3fbc2a6aa319d 100644
--- a/arch/powerpc/platforms/pseries/vas.c
+++ b/arch/powerpc/platforms/pseries/vas.c
@@ -744,6 +744,12 @@ static int reconfig_close_windows(struct vas_caps *vcap, int excess_creds,
}
task_ref = &win->vas_win.task_ref;
+ /*
+ * VAS mmap (coproc_mmap()) and its fault handler
+ * (vas_mmap_fault()) are called after holding mmap lock.
+ * So hold mmap mutex after mmap_lock to avoid deadlock.
+ */
+ mmap_write_lock(task_ref->mm);
mutex_lock(&task_ref->mmap_mutex);
vma = task_ref->vma;
/*
@@ -752,7 +758,6 @@ static int reconfig_close_windows(struct vas_caps *vcap, int excess_creds,
*/
win->vas_win.status |= flag;
- mmap_write_lock(task_ref->mm);
/*
* vma is set in the original mapping. But this mapping
* is done with mmap() after the window is opened with ioctl.
@@ -762,8 +767,8 @@ static int reconfig_close_windows(struct vas_caps *vcap, int excess_creds,
if (vma)
zap_vma_pages(vma);
- mmap_write_unlock(task_ref->mm);
mutex_unlock(&task_ref->mmap_mutex);
+ mmap_write_unlock(task_ref->mm);
/*
* Close VAS window in the hypervisor, but do not
* free vas_window struct since it may be reused
