From: Haren Myneni haren@linux.ibm.com
[ 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@linux.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://msgid.link/20230716100506.7833-1-haren@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/platforms/pseries/vas.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/platforms/pseries/vas.c b/arch/powerpc/platforms/pseries/vas.c index 880b962afc057..041a25c08066b 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. @@ -763,8 +768,8 @@ static int reconfig_close_windows(struct vas_caps *vcap, int excess_creds, zap_page_range(vma, vma->vm_start, vma->vm_end - vma->vm_start);
- 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