diff options
| author | Haren Myneni <haren@linux.ibm.com> | 2023-07-16 03:05:06 -0700 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2023-07-17 10:35:06 +1000 |
| commit | b59c9dc4d9d47b3c4572d826603fde507055b656 (patch) | |
| tree | e4832bc89acb65302113a50f95894ab8b0405428 /arch | |
| parent | fdf0eaf11452d72945af31804e2a1048ee1b574c (diff) | |
| download | lwn-b59c9dc4d9d47b3c4572d826603fde507055b656.tar.gz lwn-b59c9dc4d9d47b3c4572d826603fde507055b656.zip | |
powerpc/pseries/vas: Hold mmap_mutex after mmap lock during window close
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@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230716100506.7833-1-haren@linux.ibm.com
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/powerpc/platforms/pseries/vas.c | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/powerpc/platforms/pseries/vas.c b/arch/powerpc/platforms/pseries/vas.c index 9a44a98ba342..3fbc2a6aa319 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 |