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authorHaren Myneni <haren@linux.ibm.com>2023-07-16 13:05:06 +0300
committerMichael Ellerman <mpe@ellerman.id.au>2023-07-17 03:35:06 +0300
commitb59c9dc4d9d47b3c4572d826603fde507055b656 (patch)
treee4832bc89acb65302113a50f95894ab8b0405428 /arch/powerpc
parentfdf0eaf11452d72945af31804e2a1048ee1b574c (diff)
downloadlinux-b59c9dc4d9d47b3c4572d826603fde507055b656.tar.xz
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/powerpc')
-rw-r--r--arch/powerpc/platforms/pseries/vas.c9
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