3.16.57-rc1 review patch. If anyone has any objections, please let me know.
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From: Tejun Heo tj@kernel.org
commit d0264c01e7587001a8c4608a5d1818dba9a4c11a upstream.
While converting ioctx index from a list to a table, db446a08c23d ("aio: convert the ioctx list to table lookup v3") missed tagging kioctx_table->table[] as an array of RCU pointers and using the appropriate RCU accessors. This introduces a small window in the lookup path where init and access may race.
Mark kioctx_table->table[] with __rcu and use the approriate RCU accessors when using the field.
Signed-off-by: Tejun Heo tj@kernel.org Reported-by: Jann Horn jannh@google.com Fixes: db446a08c23d ("aio: convert the ioctx list to table lookup v3") Cc: Benjamin LaHaise bcrl@kvack.org Cc: Linus Torvalds torvalds@linux-foundation.org [bwh: Backported to 3.16: - Drop changes to aio_ring_mremap() - Signed-off-by: Ben Hutchings ben@decadent.org.uk --- fs/aio.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-)
--- a/fs/aio.c +++ b/fs/aio.c @@ -68,9 +68,9 @@ struct aio_ring { #define AIO_RING_PAGES 8
struct kioctx_table { - struct rcu_head rcu; - unsigned nr; - struct kioctx *table[]; + struct rcu_head rcu; + unsigned nr; + struct kioctx __rcu *table[]; };
struct kioctx_cpu { @@ -588,9 +588,9 @@ static int ioctx_add_table(struct kioctx while (1) { if (table) for (i = 0; i < table->nr; i++) - if (!table->table[i]) { + if (!rcu_access_pointer(table->table[i])) { ctx->id = i; - table->table[i] = ctx; + rcu_assign_pointer(table->table[i], ctx); spin_unlock(&mm->ioctx_lock);
/* While kioctx setup is in progress, @@ -765,8 +765,8 @@ static int kill_ioctx(struct mm_struct *
spin_lock(&mm->ioctx_lock); table = rcu_dereference_raw(mm->ioctx_table); - WARN_ON(ctx != table->table[ctx->id]); - table->table[ctx->id] = NULL; + WARN_ON(ctx != rcu_access_pointer(table->table[ctx->id])); + RCU_INIT_POINTER(table->table[ctx->id], NULL); spin_unlock(&mm->ioctx_lock);
/* free_ioctx_reqs() will do the necessary RCU synchronization */ @@ -827,7 +827,8 @@ void exit_aio(struct mm_struct *mm)
skipped = 0; for (i = 0; i < table->nr; ++i) { - struct kioctx *ctx = table->table[i]; + struct kioctx *ctx = + rcu_dereference_protected(table->table[i], true);
if (!ctx) { skipped++; @@ -1022,7 +1023,7 @@ static struct kioctx *lookup_ioctx(unsig if (!table || id >= table->nr) goto out;
- ctx = table->table[id]; + ctx = rcu_dereference(table->table[id]); if (ctx && ctx->user_id == ctx_id) { percpu_ref_get(&ctx->users); ret = ctx;