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Get i_mutex before cluster lock in file aio_read

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The vfs often calls filesystem methods with i_mutex held.  This creates
a natural ordering of i_mutex outside of cluster locks.  The file
aio_read method acquired i_mutex after its cluster lock, creating a
deadlock with other vfs methods like setattr.

The acquisition of i_mutex after the cluster lock was due to using the
pattern where we use the per-task lock to discover if we're the first
user of the lock in a call chain.  Readpage has to do this, but file
aio_read doesn't.  It should never be called recursively.  So we can
acquire the i_mutex outside of the cluster lock and warn if we ever are
called recursively.

Signed-off-by: Zach Brown <zab@versity.com>
This commit is contained in:
Zach Brown
2021-04-26 16:09:13 -07:00
parent 5231cf4034
commit ca320d02cb
1 changed files with 15 additions and 8 deletions
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23
kmod/src/file.c
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@@ -29,7 +29,12 @@
#include "per_task.h"
#include "omap.h"
/* TODO: Direct I/O, AIO */
/*
* Start a high level file read. We check for offline extents in the
* read region here so that we only check the extents once. We use the
* dio count to prevent releasing while we're reading after we've
* checked the extents.
*/
ssize_t scoutfs_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
unsigned long nr_segs, loff_t pos)
{
@@ -43,30 +48,32 @@ ssize_t scoutfs_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
int ret;
retry:
/* protect checked extents from release */
mutex_lock(&inode->i_mutex);
atomic_inc(&inode->i_dio_count);
mutex_unlock(&inode->i_mutex);
ret = scoutfs_lock_inode(sb, SCOUTFS_LOCK_READ,
SCOUTFS_LKF_REFRESH_INODE, inode, &inode_lock);
if (ret)
goto out;
if (scoutfs_per_task_add_excl(&si->pt_data_lock, &pt_ent, inode_lock)) {
/* protect checked extents from stage/release */
mutex_lock(&inode->i_mutex);
atomic_inc(&inode->i_dio_count);
mutex_unlock(&inode->i_mutex);
ret = scoutfs_data_wait_check_iov(inode, iov, nr_segs, pos,
SEF_OFFLINE,
SCOUTFS_IOC_DWO_READ,
&dw, inode_lock);
if (ret != 0)
goto out;
} else {
WARN_ON_ONCE(true);
}
ret = generic_file_aio_read(iocb, iov, nr_segs, pos);
out:
if (scoutfs_per_task_del(&si->pt_data_lock, &pt_ent))
inode_dio_done(inode);
inode_dio_done(inode);
scoutfs_per_task_del(&si->pt_data_lock, &pt_ent);
scoutfs_unlock(sb, inode_lock, SCOUTFS_LOCK_READ);
if (scoutfs_data_wait_found(&dw)) {