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authorOleg Nesterov <oleg@redhat.com>2014-04-30 19:02:48 +0200
committerBenjamin LaHaise <bcrl@kvack.org>2014-06-24 18:10:24 -0400
commit4b70ac5fd9b58bfaa5f25b4ea48f528aefbf3308 (patch)
treeef245ebab7daea1b368d20faa3314ab99a799022 /fs/aio.c
parentedfbbf388f293d70bf4b7c0bc38774d05e6f711a (diff)
downloadlinux-stericsson-4b70ac5fd9b58bfaa5f25b4ea48f528aefbf3308.tar.gz
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>
Diffstat (limited to 'fs/aio.c')
-rw-r--r--fs/aio.c42
1 files changed, 16 insertions, 26 deletions
diff --git a/fs/aio.c b/fs/aio.c
index 955947ef3e02..b6696462e345 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -791,40 +791,30 @@ EXPORT_SYMBOL(wait_on_sync_kiocb);
*/
void exit_aio(struct mm_struct *mm)
{
- struct kioctx_table *table;
- struct kioctx *ctx;
- unsigned i = 0;
-
- while (1) {
- rcu_read_lock();
- table = rcu_dereference(mm->ioctx_table);
-
- do {
- if (!table || i >= table->nr) {
- rcu_read_unlock();
- rcu_assign_pointer(mm->ioctx_table, NULL);
- if (table)
- kfree(table);
- return;
- }
+ struct kioctx_table *table = rcu_dereference_raw(mm->ioctx_table);
+ int i;
- ctx = table->table[i++];
- } while (!ctx);
+ if (!table)
+ return;
- rcu_read_unlock();
+ for (i = 0; i < table->nr; ++i) {
+ struct kioctx *ctx = table->table[i];
+ if (!ctx)
+ continue;
/*
- * We don't need to bother with munmap() here -
- * exit_mmap(mm) is coming and it'll unmap everything.
- * Since aio_free_ring() uses non-zero ->mmap_size
- * as indicator that it needs to unmap the area,
- * just set it to 0; aio_free_ring() is the only
- * place that uses ->mmap_size, so it's safe.
+ * We don't need to bother with munmap() here - exit_mmap(mm)
+ * is coming and it'll unmap everything. And we simply can't,
+ * this is not necessarily our ->mm.
+ * Since kill_ioctx() uses non-zero ->mmap_size as indicator
+ * that it needs to unmap the area, just set it to 0.
*/
ctx->mmap_size = 0;
-
kill_ioctx(mm, ctx, NULL);
}
+
+ RCU_INIT_POINTER(mm->ioctx_table, NULL);
+ kfree(table);
}
static void put_reqs_available(struct kioctx *ctx, unsigned nr)