aio: change exit_aio() to load mm->ioctx_table once and avoid rcu_read_lock()
On 04/30, Benjamin LaHaise wrote: > > > - ctx->mmap_size = 0; > > - > > - kill_ioctx(mm, ctx, NULL); > > + if (ctx) { > > + ctx->mmap_size = 0; > > + kill_ioctx(mm, ctx, NULL); > > + } > > Rather than indenting and moving the two lines changing mmap_size and the > kill_ioctx() call, why not just do "if (!ctx) ... continue;"? That reduces > the number of lines changed and avoid excessive indentation. OK. To me the code looks better/simpler with "if (ctx)", but this is subjective of course, I won't argue. The patch still removes the empty line between mmap_size = 0 and kill_ioctx(), we reset mmap_size only for kill_ioctx(). But feel free to remove this change. ------------------------------------------------------------------------------- Subject: [PATCH v3 1/2] aio: change exit_aio() to load mm->ioctx_table once and avoid rcu_read_lock() 1. We can read ->ioctx_table only once and we do not read rcu_read_lock() or even rcu_dereference(). This mm has no users, nobody else can play with ->ioctx_table. Otherwise the code is buggy anyway, if we need rcu_read_lock() in a loop because ->ioctx_table can be updated then kfree(table) is obviously wrong. 2. Update the comment. "exit_mmap(mm) is coming" is the good reason to avoid munmap(), but another reason is that we simply can't do vm_munmap() unless current->mm == mm and this is not true in general, the caller is mmput(). 3. We do not really need to nullify mm->ioctx_table before return, probably the current code does this to catch the potential problems. But in this case RCU_INIT_POINTER(NULL) looks better. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
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