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powerpc/pseries/vas: Hold mmap_mutex after mmap lock during window close
[ Upstream commitb59c9dc4d9
] Commit8ef7b9e176
("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:8ef7b9e176
("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>
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7bbda96776
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1 changed files with 7 additions and 2 deletions
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@ -744,6 +744,12 @@ static int reconfig_close_windows(struct vas_caps *vcap, int excess_creds,
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}
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task_ref = &win->vas_win.task_ref;
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/*
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* VAS mmap (coproc_mmap()) and its fault handler
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* (vas_mmap_fault()) are called after holding mmap lock.
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* So hold mmap mutex after mmap_lock to avoid deadlock.
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*/
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mmap_write_lock(task_ref->mm);
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mutex_lock(&task_ref->mmap_mutex);
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vma = task_ref->vma;
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/*
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@ -752,7 +758,6 @@ static int reconfig_close_windows(struct vas_caps *vcap, int excess_creds,
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*/
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win->vas_win.status |= flag;
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mmap_write_lock(task_ref->mm);
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/*
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* vma is set in the original mapping. But this mapping
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* is done with mmap() after the window is opened with ioctl.
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@ -762,8 +767,8 @@ static int reconfig_close_windows(struct vas_caps *vcap, int excess_creds,
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if (vma)
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zap_vma_pages(vma);
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mmap_write_unlock(task_ref->mm);
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mutex_unlock(&task_ref->mmap_mutex);
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mmap_write_unlock(task_ref->mm);
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/*
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* Close VAS window in the hypervisor, but do not
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* free vas_window struct since it may be reused
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