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author | 2017-08-24 15:26:01 -0400 | |
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committer | 2017-08-24 15:26:01 -0400 | |
commit | fd96b8da68d32a9403726db09b229f4b5ac849c7 (patch) | |
tree | d5085d7a2e0433e05456740c80ebaea83261480e /fs/ext4 | |
parent | ext4: fix quota inconsistency during orphan cleanup for read-only mounts (diff) | |
download | linux-fd96b8da68d32a9403726db09b229f4b5ac849c7.tar.gz linux-fd96b8da68d32a9403726db09b229f4b5ac849c7.tar.bz2 linux-fd96b8da68d32a9403726db09b229f4b5ac849c7.zip |
ext4: fix fault handling when mounted with -o dax,ro
If an ext4 filesystem is mounted with both the DAX and read-only
options, executables on that filesystem will fail to start (claiming
'Segmentation fault') due to the fault handler returning
VM_FAULT_SIGBUS.
This is due to the DAX fault handler (see ext4_dax_huge_fault)
attempting to write to the journal when FAULT_FLAG_WRITE is set. This is
the wrong behavior for write faults which will lead to a COW page; in
particular, this fails for readonly mounts.
This change avoids journal writes for faults that are expected to COW.
It might be the case that this could be better handled in
ext4_iomap_begin / ext4_iomap_end (called via iomap_ops inside
dax_iomap_fault). These is some overlap already (e.g. grabbing journal
handles).
Signed-off-by: Randy Dodgen <dodgen@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Diffstat (limited to 'fs/ext4')
-rw-r--r-- | fs/ext4/file.c | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/fs/ext4/file.c b/fs/ext4/file.c index 86ea1d92839a..197653ea6041 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -279,7 +279,20 @@ static int ext4_dax_huge_fault(struct vm_fault *vmf, handle_t *handle = NULL; struct inode *inode = file_inode(vmf->vma->vm_file); struct super_block *sb = inode->i_sb; - bool write = vmf->flags & FAULT_FLAG_WRITE; + + /* + * We have to distinguish real writes from writes which will result in a + * COW page; COW writes should *not* poke the journal (the file will not + * be changed). Doing so would cause unintended failures when mounted + * read-only. + * + * We check for VM_SHARED rather than vmf->cow_page since the latter is + * unset for pe_size != PE_SIZE_PTE (i.e. only in do_cow_fault); for + * other sizes, dax_iomap_fault will handle splitting / fallback so that + * we eventually come back with a COW page. + */ + bool write = (vmf->flags & FAULT_FLAG_WRITE) && + (vmf->vma->vm_flags & VM_SHARED); if (write) { sb_start_pagefault(sb); |