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ceph: create a new session lock to avoid lock inversion

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Lockdep was reporting a possible circular lock dependency in
dentry_lease_is_valid().  That function needs to sample the
session's s_cap_gen and and s_cap_ttl fields coherently, but needs
to do so while holding a dentry lock.  The s_cap_lock field was
being used to protect the two fields, but that can't be taken while
holding a lock on a dentry within the session.

In most cases, the s_cap_gen and s_cap_ttl fields only get operated
on separately.  But in three cases they need to be updated together.
Implement a new lock to protect the spots updating both fields
atomically is required.

Signed-off-by: Alex Elder <elder@dreamhost.com>
Reviewed-by: Sage Weil <sage@newdream.net>
This commit is contained in:
Alex Elder
2012-01-12 17:48:10 -08:00
committed by Sage Weil
parent 32852a81bc
commit d8fb02abdc
4 changed files with 14 additions and 9 deletions
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4
fs/ceph/caps.c
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@@ -641,10 +641,10 @@ static int __cap_is_valid(struct ceph_cap *cap)
unsigned long ttl;
u32 gen;
spin_lock(&cap->session->s_cap_lock);
spin_lock(&cap->session->s_gen_ttl_lock);
gen = cap->session->s_cap_gen;
ttl = cap->session->s_cap_ttl;
spin_unlock(&cap->session->s_cap_lock);
spin_unlock(&cap->session->s_gen_ttl_lock);
if (cap->cap_gen < gen || time_after_eq(jiffies, ttl)) {
dout("__cap_is_valid %p cap %p issued %s "