mirror of https://github.com/torvalds/linux.git
292a2bcd17
If shrink_dcache_tree() finds a dentry in the middle of being killed by another thread, it has to wait until the victim finishes dying, gets detached from the tree and ceases to pin its parent. The way we used to deal with that amounted to busy-wait; unfortunately, it's not just inefficient but can lead to reliably reproducible hard livelocks. Solved by having shrink_dentry_tree() attach a completion to such dentry, with dentry_unlist() calling complete() on all objects attached to it. With a bit of care it can be done without growing struct dentry or adding overhead in normal case. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQQqUNBr3gm4hGXdBJlZ7Krx/gZQ6wUCaec/ugAKCRBZ7Krx/gZQ 6y77AP9l/IL36Ic45p45FCTirA6LFyIvZ5Gixm3Xk64Pi1Y3nAEAqQ5UOVnJc907 RyrCpcI6vnO8a67MptchOxK9d1bIxQw= =A8JL -----END PGP SIGNATURE----- Merge tag 'pull-dcache-busy-wait' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs Pull dcache busy loop updates from Al Viro: "Fix livelocks in shrink_dcache_tree() If shrink_dcache_tree() finds a dentry in the middle of being killed by another thread, it has to wait until the victim finishes dying, gets detached from the tree and ceases to pin its parent. The way we used to deal with that amounted to busy-wait; unfortunately, it's not just inefficient but can lead to reliably reproducible hard livelocks. Solved by having shrink_dentry_tree() attach a completion to such dentry, with dentry_unlist() calling complete() on all objects attached to it. With a bit of care it can be done without growing struct dentry or adding overhead in normal case" * tag 'pull-dcache-busy-wait' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: get rid of busy-waiting in shrink_dcache_tree() dcache.c: more idiomatic "positives are not allowed" sanity checks struct dentry: make ->d_u anonymous for_each_alias(): helper macro for iterating through dentries of given inode |
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